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HomeMy WebLinkAbout3184; CANNON ROAD WEST; LEAST BELL'S VIREO AND WILLOW FLYCATCHER MONITORING REPORT; 2002-11-08Least Bell's Vireo and Willow Flycatcher Surveys and Monitoring 2002 Monitoring Report Cannon Road Extension Wetland Mitigation Project Macario Canyon, Carlsbad, San Diego County, California City Project No. 3184 Report prepared for the City of. Carlsbad Least Bell's vireo (Vireo belliipusilus), Photograph by Anthony Mercieca Under Contract to: Native Landscape, Inc. 9746 Tamarack Escondido, CA 92029 Prepared by: Varanus Biological Services, Inc. 7920 Silverton Avenue, Suite D San Diego, CA 92126 RECEIVED JAN 092003 EFEERING DEPARTMENT 1 8 November 2002 INTRODUCTION Least Bell's vireos (Vireo bellii pusillus) occur as seasonal migrants and as a breeding species within Macario Canyon, a small north San Diego County, California riparian drainage that flows into Agua Hedionda Lagoon (Varanus Biological Services 1999a). Between March and August 2002, Varanus Biological Services (Varanus) conducted the fifth and final year of a five-year Macario Canyon least Bell's vireo study. Varanus conducted presence/absence surveys and nest monitoring in partial fulfillment of biological mitigation requirements for the City of Carlsbad's (City) Cannon Road Extension Project under terms agreed to as a result of Section 7 consultation with the U.S. Fish & Wildlife Service (FWS). In 2002, Varanus conducted the vireo work weekly between 22 March and 30 August 2002. The willow flycatcher (Empidonax trail/ii) is also known to occur in Macario Canyon as a migrant species (Tetra Tech 1996; Varanus Biological Services 1998a, 1999a, 2000a). As an adjunct to their vireo work, Varanus conducted presence/absence surveys for willow flycatcher in the project area each year of the study, between 1 May and 20 July 2002. Willow flycatcher surveys were not a component of the project mitigation and not required by the resource agencies, however Varanus considered the surveys to be warranted because of recent willow flycatcher records and the occurrence of, albeit minimal in size and marginal in quality, suitable breeding habitat within the canyon. Willow flycatcher survey methods followed the current protocols recommended by the FWS (Sogge et a! 1997 as amended) and protocol surveys were augmented by weekly passive surveys conducted concurrently with least Bell's vireo surveys and monitoring. • DESCRIPTION OF STUDY AREA .1• Macario Canyon is located in northwest San Diego County, California. The canyon parallels Faraday Avenue with its headwaters about one-half mile north of the Faraday intersection with College Boulevard in the City of Carlsbad. This small watershed flows northwest into the eastern edge of Agua Hedionda Lagoon (Figure 1). Approximately 250 acres in size, the study area is a mosaic of wetland and upland habitats composed primarily of Southern Willow Scrub, with lesser amounts of Southern Cottonwood-willow Riparian Forest with patchy South Coast and Valley Freshwater Marsh surrounded by non-native grasslands, I Final Report: Year 5, LBVi/\ViFl Surveys 1 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 8 November 2002 owni Ip E Figure 1: Regional Location of Macario Canyon 471000mE. WGS84 Zone 1 J 476000 z NO TL rpon Xk\\ 4j1c LA 'o co Ar \i l ilLi1LI, ix .. ;•. , 2 J-(( I ) z E L. J I U7T E — \\\% ) (-, N &l! 1/ :10 .. ,:•• \, 'L c) u' —i o •-•- . .•. •.; .'. 0 0 co co 'Aw : 4 71000mE. WGS84 Zone 1 J 476000mE. *,P.AD3 0.0 05 1.0 15 2.0 25 3.0 35 miles LI 11111 I 130 0 1 2 3 4 5 k Punted from TOPO! 02001 National Geogphic Holdñtgs (www.topocom) Final Report Year 5, LBVi/WiFl Surveys 2 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services agricultural fields, and disturbed Diegan Coastal Sage Scrub. Southern Willow Scrub dominates the upper (southern) portion of the canyon. (Habitat designations follow Holland 1986.) Habitat quality varies, ranging from relatively undisturbed pockets of riparian forest to heavily disturbed and degraded areas that are subject to frequent human activity and are characterized by exotic plant species such as pampas grass (Cortaderia selloana) and tamarisk (Tamarix sp.). Dominant plant species within the study area are arroyo willow (Salix lasiolepis), Goodding's black willow (S. gooddingii), Fremont cottonwood (Populusfremontii), chaparral broom (Baccharis pilularis), broom baccharis (B. sarothroides), and cattail (Typhci sp.). Natural History Natural History of the Least Bell's Vireo and the Willow Flycatcher Least Bell's Vireo Least Bell's vireos are small migratory songbirds that are obligate summer residents of riparian habitat within Southern California and Northwestern Baja California, Mexico. Historically found throughout California from the northern Sacramento Valley south into Baja California, populations of the least Bell's vireo suffered from extensive habitat destruction and brood parasitism from the brown-headed cowbird (Molothrus ater) (Unitt 1984). The least Bell's vireo experienced dramatic declines in California between the 1940's and subsequent listing of the vireo as a protected species in the 1980's (U. S. Fish and Wildlife Service 1986), The State of California listed the least Bell's vireo as an endangered species in 1980 and it became federally listed as endangered in 1986 (U.S. Fish and Wildlife Service 1986). Since its listing and subsequent recovery actions, U. S. populations of the least Bell's vireo have increased throughout its range (U.S. Fish and Wildlife Service 1998). Willows (Salix spp.) are the most commonly used vegetation for nesting and feeding by least Bell's vireos. Other plant species used for nesting and foraging are the California wild rose (Rosa calfornica), poison oak (Toxicodendron diversilobum), chaparral broom, laurel sumac (Malosma laurina), and coast live oak (Quercus agrfolia). Franzreb (1989) reports that a low, dense shrub layer is considered essential for nesting, and nests are usually placed approximately one meter above the ground. Also, most nest sites are located near the edges of thickets, usually attached to a horizontal or pendant branch. Least Bell's vireos may also forage in uplands, including coastal sage scrubs and mesquite bosques, adjacent to breeding sites. They may also . Final Report: Year 5, LBVi/WiFl Surveys Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 8 November 2002 nest in exotic invasive vegetation such as black mustard (Brassica nigra) and giant reed (Arundo donax), species that have recently become widespread in areas of disturbance throughout coastal southern California. Willow Flycatcher Willow flycatchers have been recognized taxonomically as at least four distinct sub- species or race&(Unitt 1987; Browning 1993). Of the four sub-species, only two are typically found in San Diego County: The northwestern willow flycatcher (K t. brewsteri), a relatively common migrant, and the southwestern willow flycatcher (E. 1. extimus), a rare local breeding sub-species. Like Bell's vireo, willow flycatcher populations also declined in the latter part of the 20th century primarily because of widespread habitat destruction and fragmentation. In response to its decline, the southwestern willow flycatcher was listed as an endangered species by the federal government (US. Fish and Wildlife Service 1995). Both the northwestern and southwestern willow flycatchers are listed as endangered by the State of California. The southwestern willow flycatcher is a riparian obligate during the breeding season. This species occurs primarily in older or mature riparian habitats, typically preferring streamside associations of willow (Salix spp.), ash (Fraxinus spp.), and alder (Alnus spp.), and other riparian vegetation. Some populations thrive where the riparian vegetation is dense throughout; however in general, habitats that combine a dense overstory, uniform native herbaceous understory, and open areas for foraging appear to be optimal. One San Diego County population is unique in that coast live oaks (Quercus agrifolia) serve as the preferred nest substrate, however this preference is not expected elsewhere and appears to be related to that population's similarly unique history (Haas in press). Southwestern willow flycatchers have also been found to nest in exotic tree species including Russian olive (Eiaeagnus angustifoiia) and salt cedar (Tamarix spp.). Several other features play important roles in determining the suitability of a site for this flycatcher: Typically breeding habitat is more than 10 meters (30 feet) wide and associated with open or running water (Sogge et al 1997), or minimally saturated soils that persist through the breeding season. Sycamore woodlands, lacking an herbaceous understory (typically replaced by upland vegetation such as buckwheat (Eriogonuin spp.) and redberry (Rhamnus spp.), are not suitable breeding habitat. Final Report: Year 5, LBViIWiFI Surveys Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 8 November 2002 Ell I I I I METHODS Least Bell's Vireo Survey Methods I Of four described subspecies, only one form of Bell's vireo, the least Bells vireo, occurs and breeds in southern California. Therefore there is virtually no confusion regarding the sub- specific identity of Bell's vireos encountered during breeding season surveys in coastal southern California. To survey for the least Bell's vireo, one or more surveyors (working independently) I walked slowly along the edge of suitable riparian habitats within Macario Canyon. Every 50 meters, the surveyor stopped and listened for the song of territorial and/or advertising (that is, I mate-seeking) male least Bell's vireos. Presence/absence surveys focus on detecting the song of adult males of the species. Adult male least Bell's vireos are typically extremely vocal throughout the breeding season, and especially upon or soon after arrival at their breeding grounds. Transient least Bell's vireos sing, as do residents. Therefore during any one survey it is possible to detect a transient Bell's vireo. FWS guidelines recommend a series of eight surveys, and repeated contacts with vocalizing birds in proximate areas over the 80-day survey period are typically indicative of I resident male least Bell's vireos. We conducted our surveys weekly providing even more thorough coverage. Female least Bell's vireos are often difficult to detect during surveys, and more I typically found when studying territories over longer observation periods (for example, during spot-mapping exercises). If we found that a least Bell's vireo was present during only one survey, I we considered the observation to be that of a transient bird. The number of surveys, in conjunction with the loquaciousness of the least Bell's vireo is sufficient that we do not utilize pre-recorded I tapes to determine presence or absence. Varanus conducted sur'eys in 2002 for least Bell's vireo on a weekly basis beginning 22 I March and continuing until 30 August. We generally conducted our surveys between 0600 and 1100 hours. As a result of our weekly surveys we determined the number of vireos present and I breeding status in each territory. When found, we discreetly marked with survey flagging the areas where we observed least Bell's vireos. We also recorded a Global Positioning System (GPS) I waypoint using a hand-held GPS recorder accurate to ±5 meters. I . I Final Report: Year 5, LBVi/WiFl Surveys . . 5 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services I 8 November 2002 .. . Southwestern Willow Flycatcher Survey Methods Several forms of the willow flycatcher migrate to and through southern California. All willow flycatchers are difficult to distinguish by physical characteristics alone. The Sogge protocol (Sogge et al 1997 as amended) has been designed to distinguish between summer resident (that is, potentially breeding) and continuing migrant willow flycatchers. The northwestern willow flycatcher (E. t. brewsieri), which occurs only as a migrant in southern California, is by far the most common form. Its occurrence in coastal southern California overlaps the occurrence of southwestern willow flycatchers, with its peak migration occurring between 10 May and 20 June. During this time period brewsteri and extimus may occur at the same locations, although brewsieri is frequently found in upland habitats adjacent to riparian corridors and migrating extimus rarely so. The southwestern willow flycatcher is the only subspecies that breeds in southern California. The three surveys required by FWS protocol to determine the presence of extimus involves an initial search during the period when willow flycatchers are most vocal with follow-up surveys during a time period when only the southwestern willow flycatcher would be expected, and before the southward migration of other subspecies begins. When conducting the surveys, a permitted surveyor walked slowly along the edge of all suitable southwestern willow flycatcher breeding habitats within Macario Canyon. Willow flycatcher presence/absence surveys focus on detecting the song and calls of adults of the species. Therefore, when in potentially suitable habitat the surveyor stopped every 50 meters to listen for the "ritz-a-bew" song of male and female willow flycatchers as well as other typical vocalizations including the onomatopoeic "brrrrit", "whit", and "bree-zhew" calls. If none of these calls was detected, and no willow flycatcher was observed, the surveyor then played a series of pre-recorded song and calls. The audiotape playback is designed to stimulate a response from this often-cryptic but highly territorial species. When found, we discreetly marked each willow flycatcher (of any subspecies) location with survey flagging and recorded the GPS location using a hand-held GPS accurate to ±5 meters. Determination of sub- specific status of each willow flycatcher we encountered could not be ascertained during any one visit unless evidence of breeding was observed. Without direct evidence of breeding behaviors, only if we confirmed a territory to have been occupied for most of the survey period could we presume the presence of the southwestern willow flycatcher. Final Report: Year 5, LBVi/WiFl Surveys Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 8 November 2002 on I I 1] HI F I I Our surveys for willow flycatcher were guided by survey protocols adopted by Region 1 of the FWS (Ibid.). We conducted three surveys as recommended by the current protocol where no project impacts are proposed; the first between 15 and 30 May, the second between 1 and 21 June and a third between 22 June and 20 July. William Haas conducted the "protocol" surveys, and Haas or Ingri Quon also conducted passive surveys weekly while monitoring the least Bell's vireo. All surveys were conducted between 0600 and 1100 hours. Protocol surveys for willow flycatchers have several limitations. Presence of singing willow flycatchers may be indicative of migrant, resident non-breeding, or resident breeding individuals. With current knowledge, it is impossible to distinguish between willow flycatcher subspecies by song alone, and certainly not between southwestern willow flycatchers that might use Macario Canyon as a migratory stopover versus a potential breeding site. Also, the presence of unmarked (that is, unbanded) individuals precludes determination that individuals observed during early season surveys are the same individuals present during later surveys. Moreover, the protocol focuses on elicited or spontaneous calls primarily of male willow flycatchers. Female willow flycatchers are known to elicit the prototypical "ritz-bew" or "ritz-a-bew" song and have been found to call at similar rates to male flycatcher (Yard and Brown 2000). It has been our experience that migrating female willow flycatcher' often respond to tape playback with a common but less well-recognized "whit." However, this is complicated by the fact that other Empidonax flycatchers, for example, the dusky flycatcher (E. oberholseri) and the gray flycatcher (E. wright/i), elicit a similar "whit" call. RESULTS Least Bell's Vireo Population Number and Distribution The first Varanus observation of least Bell's vireo in Macario Canyon in 2002 occurred on 20 March. Two vireo pairs were detected within the study area during 2002. Distribution of vireo territories at the northern end of the canyon in 2002 was similar to those documented between 1996 (Tetra Tech 1996) and 2001 (Varanus Biological Services 1998a, 1999a, 2000a, 2001a). Territory A_02 Territory A02 (occupied by Pair A02) encompassed older riparian scrub in the vicinity of Final Report: Year 5, LBVi/WiFI Surveys 7 Cannon-Road Extension Wetlands Mitigation Project Varanus Biological Services 8 November 2002 8 I Cowbird Trap #1 (Latitude: 33.13778, Longitude: 117.30694, Figure 2) and included portions of the north end of the newly established North Mitigation Area. Nest A102 was placed I approximately 1 meter above the ground in chaparral broom (Baccharis pilularis). The nest was I ., abandoned prior to egg deposition. The pair's second nest, Nest A2_02, was placed 1.2 meters above the ground in a young but tall (7.2 meters) arroyo willow at the northwestern edge of the I North Mitigation site. Ingri Quon detected two vireo fledglings on 24 June. - The male of this pair had been banded in 2001 (B. Sharp, D. Kisner; U. S. Geological I .Survey) with a black/yellow split color plastic band over a silver (FWS) metal band on the left leg and a dark blue/white split color plastic band on the right leg. Figure 2: Least Bell's Vireo Locations Territory B02 Although the female was rarely observed, a second pair of vireos occupied a territory in the vicinity of Cowbird Trap #3 (Latitude: 33.13444, Longitude: 117.30722, Figure 2). The male of this territory was first observed in early April. As in 2001, no indication of breeding behavior was detected until early June. Haas found an active nest with two vireo eggs on 9 June. The nest was located in an arroyo willow at the edge of a small opening that bordered a dried area of freshwater marsh vegetation within 2 meters of the 2001 nest. Two vireos fledged from this nest in late June, and first observed on 2 July. The fledglings were, however, never again observed while the adult male was detected through the end July. Nest Success and Productivity We found three vireo nests during the 2002 season. Two nests were built in arroyo willow and one in chaparral broom. All were situated approximately 1 meter above the ground (Appendix A, Table 1). Pair A_02 built one successful nest in two attempts (50% nest success). In the two nests two eggs yielded two fledglings (100% fledging success). Pair B_02 built one known nest that contained two eggs and fledged two young (100% nest success, 100% fledging success). Of the three known Macario Canyon 2002 nests, two were successful (67% nest success). Of four eggs deposited in two nests, all four resulted in successfully fledged young (100% fledging success). Nest Site Characteristics I We have documented use of only two plant species as nest substrate by Macario Canyon least Bell's vireo, arroyo willow and chaparral broom. In 2002 vireos once again used these I species as their nesting substrate; two nests were placed in arroyo willow, one in chaparral broom. Cowbird Parasitism In 2002 Varanus conducted the final year of cowbird trapping in Macario Canyon. Between 15 March and 16 July 2002, we captured a total of 29 cowbirds, 23 adult males, 7 adult females, and 2 juveniles. Although cowbirds were detected in the study area throughout the Final Report: Year 5, LBViIWjFI Surveys 9 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 8 November 2002 :. breeding season, no incidents of brown-headed cowbird nest parasitism of least Bell's vireo were detected in Macario Canyon .during 2002. . I Willow Flycatcher In 2002 we failed to again (as in 2001 surveys) detect willow flycatchers during any of our surveys. I DISCUSSION Onset of Macario Canyon least Bell's vireo nesting in 2002 was relatively late, and I number of nests attempts few. Number of eggs deposited per nest was below average for Macario vireos (Appendix A, Table 1), however fledging success was maximized. Late nesting I in 2002 was reported throughout San Diego County. This is most likely related to extreme conditions following three years of drought, with 2002 having the lowest seasonal rainfall total in the recorded history of the county dating back to the period from 1 July 1850 through 30 June 1851. . Least Bell's Vireo Summary 1998 - 2002 Least Bell's vireos have exhibited poor breeding success in Macario Canyon during recent years. Two breeding pairs of vireo in Macario Canyon in 1998 failed to produce fledged young from six nest attempts; in 1999 only 2 young fledged from a total of 4 known nests. In 2000 2 young fledged from the only known nest. In 2001 at least 2 young fledged from 2 different nests. In 2002, the driest year on record for San Diego County, Bell's vireos exhibited their greatest level of success, fledging two young from each of two 2-egg nests. Inspection of the riparian restoration sites for Cannon Road Extension Project mitigation located in Macario Canyon indicate overall vigor and have been used by least Bell's vireos, casually within two years of installation, and subsequently as a portion of summer resident vireo territories in 2000, 2001, and 2002. The North Mitigation Area, planted in 1998, was used by foraging vireos in 1999. In 2000 the North Mitigation Area, after only three years of growth, was the location for the successful nest of Pair A_00. The North Mitigation Area also constituted part of the Final Report: Year 5, LBVi/WiFI Surveys Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 8 November 2002 10 successful Pair A_01 territory in 2001 and in 2002 Pair A_02 placed their nest along its western edge. Willow Flycatcher Summary, 1998 - 2002 There is no historic evidence that willow flycatchers have bred in Macario Canyon, and there are no recent records indicating breeding behavior of willow flycatcher in the general Agua Hedionda area. Numerous surveys have documented the occurrence of this species in Macario Canyon (Tetra Tech 1996; Varanus Biological Services 1998a, 1999a, 2000a). In 1999 Haas and Quon observed several willow flycatchers each week from 11 May through early June, including a maximum of 3 presumed females (based on vocalization) on 8 June. The brewsieri migration through San Diego County typically extends from 10 May through 20 June with peaks (males possibly differing from females) in late May and again in early June. We suspect that the 1999 May-June observations were primarily of migrant willow flycatchers. Following that period, Haas observed 1 to 2 flycatchers in Macario Canyon from late June through late July. Based on dates of occurrence and the regularity of location, one or both individuals that persisted in the canyon are likely to have been extimus, the southwestern willow flycatcher. No indications of breeding behavior were documented during 1999. We have found no further evidence of the southwestern willow flycatcher in Macario Canyon. Brown-headed Cowbird Summary, 1998 - 2002 Varanus has operated five cowbird traps each year from 1998 to 2002 (Varanus Biological Services 1998b, 1999b, 2000b, 2001b, 2002). The total number of cowbirds trapped fluctuated from year to year (Appendix A, Table 2). The total numbers captured (all ages and sexes) between 1998 and 2002 were 82, 41, 76, 63, and 29 respectively. The number of juvenile cowbirds likewise fluctuated with 21, 4, 25, 14, and 2 having been captured from 1998 to 2002 respectively. Although not directly correlated, the numbers of juveniles captured mirrored fluctuations exhibited by the trapped adult population. Cowbirds were detected in the study area throughout each breeding season; however, no incidents of brown-headed cowbird nest parasitism of least Bell's vireo were detected in Macario Canyon between 1998 and 2002. Final Report: Year 5, LBVi/WiFl Surveys 11 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 8 November 2002 LITERATURE CITED Browning, M. R. 1993. Comments on the taxonomy of Empidonax traillii (Willow Flycatcher). Western Birds 24:241-257. Franzreb, K. E. 1989. Ecology and conservation of the endangered least Bell's vireo. U. S. Fish and Wildl. Serv., Biol. Rep. 89(1). 17 pp. Haas, W.E. In press. Ecology of the willow flycatcher along the upper San Luis Rey River, San Diego County, California. Western Birds. Holland, D. C. 1986. Preliminary descriptions of the terrestrial natural communities of I California. State of California Department of Fish and Game, Sacramento, California. Sogge, M.K., R. M. Marshall, S. J. Sferra, and T. J. Tibbitts. 1997. A southwestern willow flycatcher natural history summary and survey protocol. Technical report NPS/NAUCPRSINRTR-97/12. National Park Service, Northern Arizona University, I Colorado Plateau Research Station. Tetra Tech, Inc. 1996. Letter report to Ms. Sherri Howard, City of Carlsbad: Cannon Road Reach I I least Bell's vireo surveys, Spring 1996. U. S. Fish and Wildlife Service. 1986. Endangered and threatened wildlife and plants. Final rule I determining endangered status for the least Bell's vireo. Federal Register 51:16474- 16482. I U. S. Fish and Wildlife Service. 1995. Endangered and threatened wildlife and plants. Final rule determining endangered status for the southwestern willow flycatcher. Federal Register 60:10694-10715. U. S. Fish and Wildlife Service. 1998. Draft recovery plan for the least Bell's vireo. U.S. Fish and Wildlife Service, Portland, OR. 139pp. Unitt, P. 1987. Empidonax trail/ii extimus: an endangered subspecies. Western Birds. 18:137-162 Varanus Biological Services. 1998a. First annual report: 5-year Least Bell's Vireo and Willow Flycatcher Surveys and Monitoring Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184, 8pp. Varanus Biological Services. 1998b. First annual report: 5-year Brown-headed Cowbird Trapping Program, Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of. Carlsbad, City Project No. 3184. 8pp. Final Report: Year 5, LBVi/WiFI Surveys 12 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 8 November 2002 Varanus Biological Services. 1999a. Second annual report: 5-year Least Bell's Vireo and Willow Flycatcher Surveys and Monitoring Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. Varanus Biological Services. 1999b. Second annual report: 5-year Brown-headed cowbird trapping program, Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. Varanus Biological Services. 2000a. Third annual report: 5-year Least Bell's Vireo and Willow Flycatcher Surveys and Monitoring Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. Varanus Biological Services. 2000b. Third annual report: 5-year Brown-headed cowbird trapping program, Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. Varanus Biological Services. 2001a. Fourth annual report: 5-year Least Bell's Vireo and Willow Flycatcher Surveys and Monitoring Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. Varanus Biological Services. 2001b. Fourth annual report: 5-year Brown-headed cowbird trapping program, Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. Varanus Biological Services. 2002. Fifth annual report: 5-year Brown-headed cowbird trapping program, Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. Yard, Helen K and Bryan T. Brown. 2000. Sexual and temporal differences in vocal behavior of nesting willow flycatchers along the Verde River, Arizona. Abstract from The Ecology and Conservation of the Willow Flycatcher Conference. 24-26 October 2000. Final Report: Year 5, LBVi/WiFl Surveys 13 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 8 November 2002 I I APPENDIX A 1 Least Bell's Vireo Breeding Summary Brown-headed Cowbird Capture Summary I I j S I 0' H I I I S . S 5 0 Final Repo: Year 5, LBVi/WiFI Su'eys 14 Cannon Road Extension Wetlands Mitigation Project S. Varanus Biological Services . 8 November 2002 . . - -. - -- - - - - - - - - - - - - - - - Table L Macario Canyon Least Bell's Vireo Breeding Summary, 1998 - 2002. Territory Nest Substrate Nest Height # Eggs # Nestlings # Fledglings BHCO Impact Breeding Summary 1998 MC-A1-98 Baccharispiluiaris Chaparral Broom 1.3 meters 3 0 0 N/A Failed: Weather (extreme wind and rain) MC-A2-98 Salix lasiolepis Arroyo willow 1.2 meters 0 0 0 N/A Failed: Abandoned (prior to egg deposition) MC-A3-98 Arroyo willow 0.9 meters 0 0 0 N/A Failed: Abandoned (prior to egg deposition) MC-A4-98 Arroyo willow 1.0 meters 2 0 0 N/A Failed: Abandoned MC-B1-98 Arroyo willow 0.8 meters 0 0 0 N/A Failed: Abandoned MC-B1-98 Arroyo willow 0.9 meters 3 3 0 N/A Failed: Destroyed (nest poorly constructed) 1999 MC-A1-99 Arroyo willow 0.8 meters 0 0 0 N/A Failed: Abandoned (nest poorly constructed) MC-B1-99 Chaparral broom 1.3 meters 3 0 0 N/A Failed: Weather (extreme wind, rain) MC-132-99 Arroyo willow 1.1 meters 2 . 2 2 -N/A Fledged two young from two eggs 2000 .. ___________ _______ ___________ ___________ _____________ MC-Al-00 Arroyo willow 1.0 meters 3 2 2 N/A Fledged two young from three eggs MC-B-00 N/A N/A N/A N/A N/A ' N/A N/A 2001 MC-A1-01 Arroyo willow' 1.1 meters - ' 3 2 .- 2 N/A Fledged two young from three eggs. MC-13-01 . N/A N/A N/A N/A N/A N/A N/A MC-1C-01 Arroyo willow ' 0.9 meters 2 2 - 2 N/A Fledged two young from two eggs. Final Report: Year 5, LBVi/\ViFI Surveys . ' 15 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services - 8 November 2002 - - - - - - - - - - - - - - - - - - - - - Territory Nest Substrate Nest Height # Eggs # Nestlings # Fledglings BHCO Impact Breeding Summary 2002 MC-Al-02 Chaparral Broom 1.0 meters N/A N/A N/A N/A Nest abandoned prior to egg deposition MC-A2-02 Arroyo willow 1.2 meters 2 2 2 N/A Fledged two young from two eggs. MC-BI-02 Arroyo willow 0.9 meters 2 2 2 N/A Fledged two young from two eggs. S. lasiolepis = 12 Avg. height Avg. # Avg. # Avg. # Cowbird TOTALS Eggs Nestlings Fledges Parasitism B. pilularis = 3 1.0 meters 1.7 1.0 0.8 None Table 2. Brown-headed cowbird trapping results for Macario Canyon, Carlsbad, California CATEGORY YEAR 1998 1999 2000 2001 2002 All Years BHCO, Captured - Adult Female 30 10 20 19 7 86 BHCO, Captured - Adult Male 32 33 36 46 23 170 BHCO, Captured - Juvenile 21 4 25 14 2 66 Total BHCO Captured 83 47 81 79 32 322 BHCO, released (banded) 0 2 0 0 0 2 BHCO, Net loss attributed to escape or unaccounted for depredation. 1 4 5 6 3 19 BHCO removed from Macario - Canyon and euthanized 82 41 76 63 29 301 Final Report: Year 5, LBVi/WiFl Surveys 16 Cannon Road Extension Wetlands Mitigation Project - - \'aranus Biological Services 8 November 2002 Least Bell's Vireo and Willow Flycatcher Surveys and Monitoring 2001 Monitoring Report Cannon Road Extension Wetland Mitigation Project Macario Canyon, Carlsbad, San Diego County, California City Project No. 3184 Report prepared for the City of Carlsbad Least Bell's vireo (Vireo beffli pusifius) Photograph by Anthony Mercieca Under Contract to: Native Landscape, Inc. 9746 Tamarack Escondido, CA 92029 Prepared by: Varanus Biological Services, Inc. 7950 Silverton Avenue, Suite 116 San Diego, CA 92126 INTRODUCTION Least Bell's vireos (Vireo bellii pusillus) have been documented as seasonal migrants and as a breeding species within Macario Canyon, a small north San Diego County, California riparian drainage that flows into Agua Hedionda Lagoon (Varanus Biological Services 1999a). Between March and August 2001, Varanus Biological Services (Varanus) conducted the fourth year of a five-year presence/absence survey for and nest monitoring of the least Bell's vireo in Macario Canyon. Varanus conducted the surveys and nest monitoring in partial fulfillment of biological mitigation requirements for the City of Carlsbad's (City) Cannon Road Extension Project (Project) under terms agreed to as a result of Section 7 consultation with the U.S. Fish & Wildlife Service (FWS). Varanus conducted the vireo work between 22 March and 30 August 2001. The willow flycatcher (Empidonax traillii) is also known to occur in Macario Canyon as a migrant species (Tetra Tech 1996; Varanus Biological Services 1998a, 1999a, 2000a). As an adjunct to their vireo work, Varanus conducted presence/absence surveys for willow flycatcher in the project area between 1 May and 10 July 2001. Willow flycatcher surveys were not a component of the project mitigation and not required by the resource agencies, however Varanus considered the surveys to be warranted because of recent willow flycatcher records and the occurrence, albeit marginal, of suitable breeding habitat within the canyon. Willow flycatcher survey protocols exceeded those currently recommended by the FWS (Sogge et a! 1997) as protocol surveys were augmented by weekly passive surveys conducted concurrently with least Bell's vireo surveys and monitoring. Least Bell's vireos are small migratory songbirds that are obligate summer residents of riparian habitat within Southern California and Northwestern Baja California, Mexico. Historically found throughout California from the northern Sacramento Valley south into Baja California, populations of the least Bell's vireo suffered from extensive habitat destruction and brood parasitism from the brown-headed cowbird (Molothrus ater) (Unitt 1984). The least Bell's vireo experienced dramatic declines in California between the 1940's and subsequent listing of the vireo as a protected species in the 1980's (U. S. Fish and Wildlife Service 1986). The State of California listed the least Bell's vireo as an endangered species in 1980 and it became federally Final Report: Year 4, LBVifWiFl Surveys 1 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 1 December 2001 listed as an endangered species in 1986 (U.S. Fish and Wildlife Service 1986). Since its listing and subsequent recovery actions, U. S. populations of the least Bell's vireo have increased throughout its range (U.S. Fish and Wildlife Service 1998). Willow flycatchers have been recognized taxonomically as at least four distinct sub-species or races (Unitt 1987; Browning 1993). Of the four sub-species, only two are typically found in San Diego County: the northwestern willow flycatcher (E. t. brewsteri), a relatively common migrant, and the southwestern willow flycatcher (E. t. extimus), a rare local breeding sub-species. Like Bell's vireo, willow flycatcher populations also declined in the latter part of the 20th century primarily because of widespread habitat destruction and fragmentation. In response to its decline, the southwestern willow flycatcher was listed as an endangered species by the federal government (U.S. Fish and Wildlife Service 1995). Both the northwestern and southwestern willow flycatchers are listed as endangered by the State of California. Description of Study Area Macario Canyon is located in the northwestern portion of San Diego County. The canyon follows Faraday Avenue north starting about one-half mile north of its intersection with College Boulevard in Carlsbad. The waters carried by this small watershed flow northwest into the eastern edge of Agua Hedionda Lagoon (Figure 1). Approximately 250 acres in size, the study area is a mosaic of wetland and upland habitats composed primarily of Southern Willow Scrub, with lesser amounts of Southern Cottonwood-willow Riparian Forest with patchy South Coast and Valley Freshwater Marsh surrounded by non-native grasslands, agricultural fields, and disturbed Diegan Coastal Sage Scrub. The upper (southern) reaches of the canyon are dominated by Southern Willow Scrub (habitat designations follow the Holland (1986)). Habitat quality varies and ranges from relatively undisturbed pockets of riparian forest to heavily disturbed and degraded areas that are subject to frequent human activity and are characterized by exotic plant species such as pampas grass (Cortaderia selloana) and tamarisk (Tamarix sp.). Dominant plant species within the study area are arroyo willow (Salix lasiolepis), Goodding's black willow (S. gooddingii), Fremont cottonwood (Populus fremontii), broom baccharis (Baccharis sarothroides) and cattail (Typha sp.). Final Report: Year 4, LBViIWiFl Surveys 2 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 1 December 2001 471000mE. WGS84 Zone uS 4 7600 0 0 0 N M E 0 0 0 N CO z E 0 0 0 LA () 2 E 0 0 0 2 E 0 0 0 .1 0 0 0 N '0 0) 2 E 0 0 0 ID Cl) 2 E 0 0 0 If) 0) 2: E 0 0 0 (Y) C,) z E 0 0 0 '-I 4 71000mE. WGS84 Zone uus 476000mE. TM*lTuTM 0.0 0.5 1.0 1.5 2.0 25 3.0 3.5 miles I I - II •'''''I''''''I'''''' I,,,,,,,I ,,,,,, I 1113° 0 1 2 3 4 5 k Printed from TOPO' ©2001 National Geographic Holdings (www.topo.com) Final Report: Year 4, LBVi/WiFl Surveys Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services I December 2001 3 METHODS Least Bell's Vireo Varanus conducted surveys in 2001 for least Bell's vireo on a weekly basis beginning 22 March and continuing until 30 August. Adult male least Bell's vireos are typically extremely vocal, especially upon or soon after arrival at their breeding grounds. Surveys for this species were conducted passively (that is, without assistance of pre-recorded tape playback or scolding ("spishing" or "pishing", etc.) by slowly walking along suitable habitat, stopping every 50 meters to listen for vireos singing spontaneously. We generally conducted our surveys between 0600 and 1100 hours. As a result of our weekly surveys we determined the number of vireos present and breeding status in each territory. - Willow Flycatcher Surveys for willow flycatcher were guided by survey protocols adopted by Region 1 of the FWS (Sogge et al 1997). We conducted surveys using audio playback of pre-recorded willow flycatcher song while walking slowly along and within suitable willow flycatcher habitat. Three surveys are recommended by the current protocol where no project impacts are proposed; the first between 15 and 30 May, the second between 1 and 21 June and a third between 22 June and 10 July. William Hans conducted the "protocol" surveys, and Haas, Ingri Quon, or Brennan Mulrooney also conducted passive surveys weekly while monitoring the least Bell's vireo. All surveys were conducted between 0600 and 1100 hours. Protocol surveys for will flycatchers have several limitations. Presence of singing willow flycatchers may be indicative of migrant, resident non-breeding, or resident breeding individuals. With current knowledge, it is impossible to distinguish between willow flycatcher subspecies by song alone, and certainly not between southwestern willow flycatchers that might use Macario Canyon as a migratory stopover versus a potential breeding site. Also, the presence of unmarked (that is, unbanded) individuals precludes determination that individuals observed during early season surveys are the same individuals present during later surveys. Moreover, the protocol focuses on elicited or spontaneous calls primarily of male willow flycatchers. Female willow flycatchers are known to elicit the prototypical "fitz-bew" or "fitz-a-bew" song and have been found to call at similar rates to male flycatcher (Yard 2000). It has been our experience that Final Report: Year 4, LBVi/WiFI surveys 4 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 1 December 2001 migrating female willow flycatcher often respond to tape playback with a common but less well- recognized "whit." However, this is complicated by the fact that other Empidonax flycatchers, for example, the dusky flycatcher (E. oberholseri) and the gray flycatcher (E. wrightii), elicit a similar "whit" call. Haas, Quon, and Muirooney are familiar with the biology and calls of all three species. RESULTS •. Least Bell's Vireo Population Number and Distribution The first Varanus observation of least Bell's vireo in Macario Canyon in 2001 occurred on 31 * March, the second year in a row that we detected a vireo in Macario on this date. A total of 2 breeding pairs and one lone male vireo were detected within the study area during 2001. Distribution of vireo territories at the northern end of the canyon in 2001 was similar to those documented between 1996 (Tetra Tech 1996) and 2000 (Varanus Biological Services 1998a, 1999a, 2000a). The two 2001 breeding territories were similar to territories established in 1998, 1999, 2000. . - At least 1 additional individual presumed to be an adult male migrant (sensu en route to breeding habitat at a more northerly locale) or transient (sensu searching for a territory in the near vicinity) based on singing activity, was also detected within the study area. Female transients a.re typically more difficult to detect than males because of reduced singing activity and more discreet feeding . behaviors. Transient females, therefore, may have passed through the study area undetected. Status of male vireos as migrants or transients was based on their presence in Macario Canyon for. less than 14 days. Territory AO 1 Territory A_01. (occupied by Pair A_01) encompassed older riparian scrub in the vicinity of Cowbird Trap #1 and included portions of the north end of the newly established North Mitigation Area (Figure 2). On 10 May W. Hans found a nest within this territory. The nest was located approximately 1 meter above the ground in a .4.0-meter tall arroyo willow at the edge between mature willow scrub and the North Mitigation Area.. The nest contained 3 vireo eggs. On 1 June Brennan Final Report: Year 4, LBVi/WiFl Surveys S S 5 5 Cannon Road Extension Wetlands Mitigation Project S Varanus Biological Services S S 1 December 2001 5 Mulrooney observed an adult vireo carrying food to the nest. At least two vireos fledged from this nest on approximately 4 June. Territory BO 1 A solitary Bell's vireo (Territory B_01) occupied a "territory" that included the southern portion of the North Mitigation Area and it frequently was active in portions of Territory A_01 (Figure 2). This individual possessed a single blue metal band on its left leg. We never observed a second vireo in association with this vocal individual, nor did we find evidence of a nest, nor of this individual in the presence of a juvenile vireo. Based on the size of this individual's territory, its overlap with the known breeding Territory A_O 1, and its vocal behaviors we surmised that this individual was an unpaired male. Territory CO 1 Although the female was rarely observed, a second pair of vireos occupied a territory in the vicinity of Cowbird Trap #3 (Figure 2). The male of this territory was first observed in mid- April. It is possible that the female of this pair arrived at the site relatively late in the breeding season as neither Haas, nor Muirooney, nor Quon observed a second vireo or any indication of breeding behavior until early June. Hans found an active nest with two vireo eggs on June 12. The nest was located in an arroyo willow at the edge of a small opening that bordered a dried area of freshwater marsh vegetation. Two vireos fledged from this nest on 30 June and at least one fledgling was observed following the adult male until mid-August. Banded Vireos During a vireo survey on 26 April, Hans observed that one of the adult male vireos in Macario Canyon was banded with a dark blue metal band on the left leg. All other vireos observed in the canyon were unbanded. On 3 Aug 01 Bryan Sharp and David Kisner captured 2 adult males (via mist net) in the study area. One of the birds they captured was the banded bird. On inspection of the band number they determined it to have been banded in 1999 at Guajome Regional Park in Oceanside, San Diego County, CA. This is a dispersal distance of approximately 12km. The blue-banded male received a complementary yellow plastic band on the right leg. On the other adult male bird they placed a black/yellow split color plastic band over a silver (U. S. Fish and Wildlife Service) metal band on the left leg and a darkblue/white split color plastic band on the right leg. These bands will allow the birds to be identified without capture if they are seen in the Final Report: Year 4, LBVi/WiFl Surveys 6 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 1 December 2001 VU a r 0 0 0 r-. 0 C., ri 0 0 0 0 C., 470000m E, 471000mE. WGS84 Zone 11 472000mE, TerntoiyC oil ci Z..' '• . Farr tank \ \\ - 470000mE. 471000mE. WGS84 Zone 115 472000m E. TN/MN — 5 — — 1 MILE- 1/130 0 — _1000 FEET 0 5(K) — 1000 METERS Printed from TOPO' @2001 National Geogmphic Holdings (www.topo.com) Figure 2. Least Bell's Vireo 2001 territories, Macario Canyon, Carlsbad, CA. study area in the future. Sharp and Kisner banded the vireos under the auspices of FWS 10(a)1(A) permit number PRT-22372 issued to Dr. Barbara Kus of the U. S. Geological Survey. Nest Success and Productivity We found two vireo nests during the 2001 season. In both cases the nests were built in arroyo willow and situated approximately 1 meter above the ground. Pair A-01 built at least one successful nest that contained three eggs and fledged at least two young. Pair C-01 built at least one nest that contained two eggs and fledged at least one young. Qf the two known nests, both Final Report: Year 4, LBViIWiF1 Surveys 7 Cannon Road Extension Wetlands Mitigation Project -- Varanus Biological Services 1 December 2001 (100%) successfully produced fledged young. Of five eggs deposited,, at least three (60%) produced fledglings. Nest Site Characteristics We have documented use of only two plant species as nest substrate by Macario Canyon least .Bell's vireo, arroyo willow and chaparral broom (Baccharispilularis). In 2001 vireos once again chose to place nests in arroyo willow. Cowbird Parasitism '. - In 2001 Varanus conducted the fourth in a series of five consecutive seasons of brown-headed cowbird trapping. Varanus has operated a total of five cowbird traps each year.. Cowbird trapping is concurrent with vireo surveys and monitoring .(Varanus Biological Services 1998b, 1999b, 2000b). Between 15 March and 16 July 2001, we captured a total of 76 cowbirds, 45 adult males, 17 adult females, and 14 juveniles.. The total number of cowbirds observed and captured was slightly less in 2001 than in 2000 (a total of 81). Although cowbirds were detected in the study area throughout the breeding season, no incidents of brown-headed cowbird nest parasitism of least Bell's vireo were detected in Macario Canyon during 2001. . Willow Flycatcher In 2001 we failed to detect willow flycatchers during any of our surveys. There is no historic evidence that willow flycatchers have bred in Macario Canyon, and there are no recent records' indicating breeding behavior of willow flycatcher in the Agua Hedionda area. Previous surveys (Tetra Tech 1996; Varanus Biological Services '1998a, 1999a, 2000a) have documented the occurrence of this species in Macario Canyon. In 1999 W. Haas and I. Quon observed between 1 and 3 willow flycatchers each week from 11 May through early June, including a total of 3 presumed females (based on vocalization) on 8 June. The brèwsteri migration thrdugh San Diego County typically extends from 10" May through 20 June with peaks (males possibly differing from females) in late May and early June. Following that period, W. Haas observed 1 to 2 flycatchers on 23 June, 28 June and 15 July. Based on dates of occurrence and the regularity of location he suspected that 1 or both individuals that persisted in the canyon might have been ' extimus. Final Report: Year 4, LBVi/WiFl Surveys ' 8 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services I December 2001 a Least Bell's vireos have exhibited poor breeding success in Macario Canyon during recent years. Two breeding pairs of vireo in Macario Canyon in 1998 failed to produce fledged young and in 1999 only 2 young fledged from a total of 4 known nests. In 2000 2 young fledged from the only known nest. In 2001 at least 3 young fledged from 2 different nests. Inspection of the riparian restoration sites for Cannon Road Extension Project. mitigation located in Macario Canyon indicate overall vigor and suggest increased potential to support least Bell's vireo independent of surrounding development. The North Mitigation Area, planted in 1998, was used by foraging vireos in 1999. In 2000 the North Mitigation Area, after only three years of growth, was the location for the successful nest of Pair A.00. The North Mitigation Area also constituted part of the successful Pair A-01 territory in 2001 and their nest was located along its western edge. The existence of breeding vireos in Macario Canyon and their persistence is encouraging. However, after overcoming a history of reproductive failure in the mid-1990's (through 1998), several problems face this small vireo breeding site. These include the proposed residential and recreational development of the slopes surrounding Macario Canyon and nearby Agua Hedionda Creek. As development in the area proceeds, yearly monitoring will be able to document the effects of encroachment on the vireo population within the study area. We continue to believe that concurrent trapping of brown-headed cowbirds will help offset potential adverse effects of recurrent nest and fledgling losses. It is possible that the relatively large numbers of cowbirds captured in our traps in 2000 and 2001 may be related to continued disturbance along the periphery of Macario Canyon. It is also possible that nearby Agua Hedionda Creek, a larger, more complex riparian corridor than Macario Canyon, is a source for • - increased numbers of cowbirds in Macario Canyon. We recommend a review of recent traping - regimes in the vicinity of the project in order to understand the results of the cowbird trapping efforts in Macario Canyon and along Agua Hedionda Creek. •• • Final Report: Year 4, LBVIIWiFI Surveys • 9 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services : 1 December 2001 - REFERENCES Browning, M. R. 1993. Comments on the taxonomy of Empidonax traillii (Willow Flycatcher). Western Birds 24:241-257. Holland, D. C. 1986. Preliminary descriptions of the terrestrial natural communities of California. State of California Department of Fish and Game, Sacramento, California. Sogge, M.K., R. M. Marshall, S. J. Sferra, and T. J. Tibbitts. 1997. A southwestern willow flycatcher, natural history summary and survey protocol. Technical 'report NPS/NAUCPRS/NRTR-97/12. National Park Service, Northern Arizona University, Colorado Plateau Research Station. Tetra Tech, Inc. 1996. Letter report to Ms. Sherri Howard, City of Carlsbad: Cannon Road Reach I least Bell's vireo surveys, Spring 1996. U. S. Fish and Wildlife Service. 1995. Endangered and threatened wildlife and plants. Final rule determining endangered status for the southwestern willow flycatcher. Federal Register 60:10694-10715.. . . U. S. Fish and Wildlife Service. 1986. Endangered and threatened wildlife and plants. Final rule determining endangered status for the least Bell's vireo. Federal Register 51:16474-' 16482. U. S. Fish and Wildlife Service. 1998. Draft recovery plan for the least Bell's vireo. U.S. Fish and Wildlife Service, Portland, OR. 139pp. Unitt, P. 1987. Empidonax traillii extimus: an endangered subspecies. Western Birds. 18:137-162 Varanus Biological Services. 1998a. First annual report: 5-year Least Bell's Vireo and Final Report: Year 4, LBViJWiFI Surveys ' ' 10 Cannon Road Extension Wetlands Mitigation Project . Varanus Biological Services 1 December 2001 10 Willow Flycatcher Surveys and Monitoring Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. 8pp. Varanus Biological Services. 1998b. First annual report: 5-year Brown-headed Cowbird Trapping Program, Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. 8pp. Varanus Biological Services. 1999a. Second annual report: 5-year Least Bell's Vireo and Willow Flycatcher Surveys and Monitoring Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. Varanus Biological Services. 1999b. Second annual report: 5-year Brown-headed cowbird trapping program, Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. lOpp. Varanus Biological Services. 2000a. Second annual report: 5-year Least Bell's Vireo and Willow Flycatcher Surveys and Monitoring Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. Varanus Biological Services. 2000b. Second annual report: 5-year Brown-headed cowbird trapping program, Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. lOpp. Yard, Helen K and Bryan T. Brown. 2000. Sexual and temporal differences in vocal behavior of Final Report: Year 4, LBVi/WiFl Surveys 11 Cannon Road Extension Wetlands Mitigation Project Vat-anus Biological Services 1 December 2001 nesting willow flycatchers along the Verde River, Arizona. Abstract from The Ecology and Conservation of the Willow Flycatcher Conference. 24-26 October 2000. Final Report: Year 4, LBViIWiFl Surveys 12 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 1 December 2001 I. .. .1 ' I . Third Annual Report - 2000 Least Bell's Vireo and Willow Flycatcher Surveys and Monitoring Cannon Road Extension Wetland Mitigation Project U Macario Canyon, Carlsbad, San Diego County, California U * . City Project No. 3184 Report prepared for the City of Carlsbad • PCF WED DEC Jr jI PC G DEC i DEPARTMENT ENGt,NG * DEPARTMENT Least Bell's vireo (Vireo bellii pusillus) Photograph by Anthony Mercieca . . I ..,.., Under Contract to: Native Landscape, Inc. 9746 Tamarack Escondido, CA 92029 U ..' .. ..., Prepared by: - Varanus Biological Services, Inc. 7950 Silverton Avenue, Suite 116 * . . San Diego, CA 92126 U., - •, '. , * . * S " I fl H I H INTRODUCTION 1 I Least Bell's vireos (Vireo bellii pusillus) have been documented as seasonal migrants and as a breeding species within Macario Canyon, a small north San Diego County, California riparian drainage that flows into AguaHedionda Lagoon (Varanus Biological 1999). Between March and August 2000, Varanus Biological Services (Varanus) conducted the third year of a five-year presence/absence survey for and nest monitoring of least Bell's vireo in Macario Canyon. Varanus conducted the surveys and nest monitoring in partial fulfillment of biological mitigation I requirements for the City of Carlsbad's (City) Cannon Road Extension Project (Project) under terms agreed to as. a result of Section 7 consultation with the U.S.' Fish & Wildlife Service (FWS). Varanus conducted the vireo work between 31 March and 28 August 2000. I Willow flycatchers (Empidonax traillii ssp.) are also known to occur in the area as a migrant species (Tetra Tech 1996, Varanus 1998a, 1999a). As an adjunct to the vireo work, Varanus conducted presence/absence surveys for willow flycatcher in the project area. Willow flycatcher surveys were not a component of the project mitigation and not required by the resource I agencies, however the City felt the surveys were warranted. Willow flycatcher survey protocols I exceeded those currently recommended by the FWS (Sogge et a! 1997). Varanus conducted willow flycatcher surveys between 15 May and 15 August and exceeded the minimum number of surveys recommended by the protocol. I Least Bell's vireos are small migratory songbirds that are obligate summer residents of riparian habitat within Southern California and Northwestern Baja California, Mexico. Historically found I throughout California from the northern Sacramento Valley south into Baja California, populations of the least Bell's vireo suffered from extensive habitat destruction and brood parasitism from the brown-headed cowbird (Molothrus ater) (Unitt 1984). The least Bell's vireo experienced dramatic declines in California between the 1940's and subsequent listing of the vireo as a protected species in the 1980's (U. S. Fish and Wildlife Service 1986). The State of California listed the least Bell's vireo as an endangered species in 1980 and it became federally listed as an endangered species in 1986 (U.S. Fish and Wildlife Service 1986). Since its listing Final Report: Year 3, LBVi/WiFl Surveys i Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 10 December 2000 P and subsequent recovery actions, U. S. populations of the least Bell's vireo have increased throughout its range (U.S. Fish and Wildlife Service 1998). Willow flycatchers have been recognized taxonomically as at least four distinct sub-species or races (Unitt 1987; Browning 1993). Of the four sub-species, only two are typically found in San Diego County: the northwestern willow flycatcher (E. t. brewsteri), a relatively common migrant, and the southwestern willow flycatcher (E. t. extimus), a rare local breeding sub-species. Like Bell's vireo, willow flycatcher populations also declined in the latter part of the 20th century because of widespread habitat destruction. As a result, the southwestern willow flycatcher was listed as an endangered species by the federal government (U.S. Fish and Wildlife Service 1995). The relationship between willow flycatcher declines and brood parasitism by brown-headed cowbirds is unclear (W. Haas literature review). Both northwestern and southwestern willow flycatchers are listed as endangered by the State of California. Description of Study Area Macario Canyon is located in the northwestern portion of San Diego County. The canyon follows Faraday Avenue north starting about one-half mile north of its intersection with College Boulevard in Carlsbad. The waters carried by this small watershed flow northwest into the eastern edge of Agua Hedionda Lagoon (Figure 1). Approximately 250 acres in size, the study area is a mosaic of wetland and upland habitats composed primarily of Southern Cottonwood- willow Riparian Forest with patchy South Coast and Valley Freshwater Marsh surrounded by non-native grasslands, agricultural fields, and disturbed Diegan coastal Sage Scrub. The upper (southern) reaches of the canyon are dominated by Southern Willow Scrub. Habitat designations follow the Holland nomenclature (Holland 1986). Within the two major riparian habitats are patches of emergent riparian forest, freshwater marsh and baccharis scrub. Habitat quality varies and ranges from relatively undisturbed pockets of riparian forest to heavily disturbed and degraded areas that are subject to frequent human activity and are characterized by exotic plant species such as pampas grass (Cortaderia selloana) and tamarisk (Tamarix sp.). Dominant plant species within the study area are arroyo willow (Salix lasiolepis), Goodding's black willow (S. I Final Report: Year 3, LBViIWiFI Surveys Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 10 December 2000 I I I I I I I I I I I I I I I I gooddingii), Fremont cottonwood (Populus fremontii), broom baccharis (Baccharis sarothroides) and cattail (Typha sp.). Insert Figure 1. Vicinity Map with Cowbird Trap Locations #1-5 Final Report: Year 3, LBVi/WiFl Surveys 3 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 10 December 2000 1 1 METHODS Least Bell's Vireo Varanus conducted surveys in 2000 for least Bell's vireo on a weekly basis beginning 31 March and continuing until 28 August. Adult male least Bell's vireos are typically extremely vocal, especially upon or soon after arrival at their breeding grounds. Surveys for this species were conducted passively (that is, without assistance of pre-recorded tape playback or scolding ("spishing" or "pishing", etc.) by slowly walking along suitable habitat, stopping every 50 meters to listen for vireos singing spontaneously. We generally conducted our surveys between 0700 and 1100 hours. As a result of our weekly surveys we determined the number of vireos present in each territory, their breeding status and, when present, nest locations. Once found, nests were visited on a limited basis and no more than three visits were made to any nest. Typically a nest site was visited 3 times with the first visit to establish the nest location and the number and type of eggs (specifically vireo and/or cowbird) present in the nest. The second visit, approximately 10 - 14 days following the first visit was timed to determine the number of nestlings. Our third visit was timed to ascertain the number of nestlings just prior to (2 - 4 days) fledging. We confirmed nest success and number of fledges without further close approach to the nest. Ingri Quon or William Haas conducted the nest searches and monitoring. Willow Flycatcher Surveys for willow flycatcher were guided by survey protocols adopted by Region 1 of the USFWS (Sogge et al 1997). We conducted surveys using audio playback of pre-recorded willow flycatcher song while walking slowly along and within suitable willow flycatcher habitat. Three surveys are required by the current protocol; the first between 15 and 30' May, the second between 1 and 21 June and a third between 22 June and 10 July. However, Varanus conducted surveys on 4 May, 28 May, 18 June, 2, 10, and 24 July. All surveys were conducted between 0600 and 1000 hours. I I Final Report: Year 3, LBVi/WiFl Surveys Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 10 December 2000 I 4 I p I Li: Li I I I I I I I I Protocol surveys have several limitations. Presence of singing willow flycatchers may be indicative of migrant, resident non-breeding, or resident breeding status. With current knowledge, it is impossible to distinguish between willow flycatcher subspecies by song alone, and certainly not between southwestern willow flycatchers that might use Macario Canyon as a migratory stopover or potential breeding site. Also, the presence of unmarked (that is, unbanded) individuals precludes determination that individuals observed during early season surveys are the same individuals present during later surveys. Moreover, the protocol focuses on elicited or spontaneous calls primarily of male willow flycatchers. Female willow flycatchers are known to elicit the prototypical "fitz-bew" or "fitz-a-bew" song and have been found to call at similar rates to male flycatcher (Yard 2000). It has been our experience that migrating female willow flycatcher often respond to tape playback with a common but less well-recognized "whit." Even this is complicated by the fact that other Empidonax flycatchers, for example, dusky flycatcher (E. oberholseri) and gray flycatcher (E. wrightii), elicit a similar "whit" call. For these reasons, we extended our survey period and our surveys were augmented by additional observations of detected individuals to attempt to discern other behaviors and activities indicative of residency, especially nesting or other breeding activity. I . RESULTS Least Bell's Vireo I Population Number and Distribution The first Varanus observation of least Bell's vireo in Macario Canyon in 2000 occurred on 31 I March. This date of first arrival in the canyon fits the general trend of late arrival observed throughout southern California this year (Pete Famolaro, Loren Hays personal communication, and I Varanus personal observation 2000). Although we conducted surveys on a weekly basis, Varanus cowbird trap monitors Tom Myers and Alyssa Nowak collected vireo data on a daily basis. On 7 April, the first acknowledged pair of vireos was observed in the vicinity of Varanus Cowbird Trap #2 (Figure 1). A total of one breeding pair and one solitary male vireo were detected within the I study area during 2000. Distribution of vireo territories at the northern end of the canyon in 2000 I Final Report: Year 3, LBVi/WiFI Surveys 5 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 10 December 2000 I I I I I 11 was similar to those documented in 1996 by biologists Patrice Ashfield and Kim Miller (Tetra Tech 1996) and in 1998 and 1999 by Varanus (Varanus 1998a, 1999). The single 2000 vireo breeding territory was adjacent to and overlapped in part a vireo territory established in both 1998 and 1999. This territory (Pair A_00) encompassed mature riparian habitat and included portions of the newly established North Mitigation Area) east of Cowbird Traps #1 and #2. The lone male vireo (Male BOO) occupied a territory that included all of the use area used in 1999 by Pair B_99 and much of the use area occupied by. Pair A_99. Male B_00 also utilized portions of the Pair AOO use area, especially the southern portion (Figure 2). At least three additional individuals, presumed to be migrant (sensu en route to breeding habitat at a more northerly locale) or transient (sensu searching for a territory in the near vicinity) adult males based on singing activity, were also detected within the study area. Female transients are typically more difficult to detect than males because of reduced singing activity and more discreet feeding behaviors. Transient females, therefore, may have passed 'through the study area undetected. Status of male vireos as migrants or transients was based on their presence in Macario Canyon for less than 14 days. Although unmarked, it appears that at least one transient male vireo lingered in the Canyon for approximately 14 days prior to departing. This individual was observed on a daily basis within a finite area along Macario Creek for an entire two-week period (Figure 2). Territory A_0O Alyssa Nowak detected a singing vireo on 31 March while tending cowbird traps and conducting a focused vireo survey; The detected individual was a vocal male foraging in the vicinity of Cowbird Trap #2. The apparently solitary male foraged in the North Mitigation Area and' the mature riparian habitat of the canyon bottom. During the ensuing survey on 7 April, A. Nowak detected a female vireo with the singing male in the vicinity of Traps #1 and #2. W. Hans found a vireo nest on 4 May approximately 1 meter above the ground in a 3.5-meter tall arroyo willow in the North Mitigation Area (Figure 2). The nest contained 3 vireo eggs. On 18 May W.' Hans found 1 recently hatched (that is, less than 1-day old) nestling and 2 eggs in the nest. On 1 June W. Hans observed two "ready to fledge" nestlings in the nest. Nowak observed 2 fledges in this U . Final Report: Year 3, LBVi/WiFl Surveys Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 10 December 2000 U LI U I I I I I I I I U I I I I U H territory on 9 June. 1 I frequently during co June while a male re I I I II I I II I I I Final Report: Year 3, LBVi/WiFl Surveys Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services JO December 2000 1 7 Insert Figure 2. LBV Use Areas and 1999 2000? Territories \ Final Report: Year 3, LBVi/WiFl Surveys 8 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 10 December 2000 I Territory BOO On 26 May A. Nowak detected a singing male vireo in the vicinity of Cowbird Traps #2 and #3. This male arrived much later than both birds of Pair A_00, and for the rest of the breeding season u was never found in the company of a female. This male was last encountered on 18 August and remained vocal throughout the season. Banded Vireos No banded vireos were detected within the study area during 2000. I Nest Success Nest success (that is, the percentage of completed nest that produced at least one fledgling) in I 2000 was 100%. Pair AOO attempted to nest on one occasion mid-way through the vireo breeding season (nest construction probably occurred between 28 April and I May). The only nest constructed by AOO was placed approximately 1 meter above the ground in a 3.5-meter tall I Arroyo willow within the North Mitigation Area. Upon first inspection the nest contained 3 vireo eggs. Subsequent nest checks indicated the presence of 2 nestlings, including a visit to the nest U .just prior to fledging. We observed two fledges within the A_00 use area on 9 June and during numerous visits thereafter through 4 August. Productivity . . I We found a total of 3 eggs in 1 monitored nest. Two of the 3 eggs (67%) are known to have hatched and both hatchlings (100%) survived beyond the fledgling stage. The small number of nest attempts in 2000 when compared to 1998 and 1999 data appear to be related to the reduced number of vireos resident in the canyon. In addition, a successful nest attempt by the single pair of vireos in mid-season 2000 probably precluded late nesting attempts. I Nest Site Characteristics We have documented use of only two plant species as nest substrate by Macario Canyon least I Bell's vireo, arroyo willow and chaparral broom (Bacchaiis pilularis). The only nest found in U . Final Report: Year 3, LBVi/WiFl Surveys ., 9 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 10 December 2000 I ii I. 2000 was located in arroyo willow. The nest in arroyo willow was attached to y-shaped branches approximately 1 meter above the ground. Unlike observations we have documented from previous years of monitoring, nest placement in 2000 did not contribute to failed nest attempts. In previous years (Varanus 1998a, 1999a) nests in the vicinity of Use Area A_00 (near Cowbird Traps #s 1 and 2) had been place precariously within willow substrate and probably lead to the failure of each documented nest. I Cowbird Parasitism Varanus conducted the third in a series of five consecutive seasons of brown-headed cowbird I trapping in 2006. Varanus has operated a total of five cowbird traps each year. Cowbird trapping is concurrent with vireo surveys and monitoring (Varanus 1998b, 1999b). Although cowbirds I were detected in the study area throughout the breeding season, no incidents of brown-headed cowbird nest parasitism of least Bell's vireo were detected in Macario Canyon during 2000. The total number of cowbirds observed and captured was greater in 2000 than in 1999. Between 18 March and 25 July a total of 81 cowbirds (36 adult males, 20 adult females, and 25 juveniles) I were captured. A total of 78 cowbirds were actively removed (euthanized) from our traps in the I .canyon. Three of the 81 had escaped and/or were depredated. Especially noteworthy was the increase in number of juvenile cowbirds captured in 2000 (n=25) versus 1999 (n=3). Willow Flycatcher. I There is no historic evidence that willow flycatchers have bred in Macario Canyon, and there are no recent records indicating breeding behavior of willow flycatcher in the Agua Hedionda area. U Surveys in 1996 indicated the presence of migratory willow flycatchers on 7 June 1996 (Tetra Tech 1996). These were identified as "southwestern" willow flycatcher (E. t. extimus) however as with most migrants through San Diego County . they were probably the more common "northwestern" willow flycatcher (E. t. brewsteri) or possibly E. t. adastus the subspecies that I breeds in the California Sierras and the Great Basin. The brewsteri migration through San Diego County usually extends from 10 May through 20 June with peaks (males possibly differing from I females) in late May and early June. We found probable migrant willow flycatchers in Macario I Final Report: Year 3, LBVi/WiFl Surveys 10 Cannon Road Extension Wetlands Mitigation Project - Varanus Biological Services 10 December 2000 I I , ~ Canyon during surveys on 29 May and 5 June 1998. Observer W. Haas noted most observations I were of birds in upland habitats and accompanied by frequent "whitting", typical of migrant, especially female migrant, willow flycatchers. In 1999 W. Hans and I. Quon observed between 1 and 3 willow flycatchers each week from 11 May through early June, including a total Of 3 presumed females (based on vocalization) on 8 June. Following this period, W. Hans observed 1 to 2 flycatchers on 23 June, 28 June and 15 July. Based on dates of occurrence and the regularity of location he suspected that 1 or both individuals might have been extimus. I, In 2000 we detected only one adult willow flycatcher during the 18 June survey. We conducted our flycatcher surveys on 4 and 28 May, 18 June, 2, 10, and 24 July. The date of our single observation in 2000, our failure to rediscover any willow flycatchers during subsequent surveys, and the difficulty in distinguishing between subspecies of the willow flycatcher precludes a definite identification of the individual present in Macario Canyon in 2000. I DISCUSSION I Least Bell's vireos have exhibited poor breeding success in Macario Canyon during recent years. I Two breeding pairs of vireo in Macario Canyon in 1998, failed to produce fledged young and in 1999 2 young fledged from a total of 4 known nests. In 2000 2 young fledged from the only I known nest. The existence of breeding vireos in Macario Canyon and their persistence is an encouraging indication of its use as a successful breeding site. However, in addition to I reproductive failure in 1998, several problems face this small vireo population. These include the proposed residential and recreational development of the slopes surrounding Macario Canyon I and nearby Agua Hedionda Creek. As development in the area proceeds, yearly monitoring will be able to document the effects of encroachment on the vireo population within the study area. Initial inspection of the riparian restoration sites for Cannon Road Extension Project mitigation I located in Macario Canyon indicate overall vigor and suggest increased potential to support least Bell's vireo independent of surrounding development. The North Mitigation Area that was I planted in 1998 was used by foraging vireos in 1999, In 2000 the North Mitigation Area, after I Final Report: Year 3, LBVi/WiFl Surveys Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 10 December 2000 I I, I , I I I , I' I I I . I I I. I I I I I I I only three years of growth was the location for the successful nest of Pair A_00. We continue to believe that concurrent trapping of brown-headed cowbirds will help offset potential adverse effects of recurrent nest and fledgling losses. It is possible that increased numbers of cowbirds captured in our traps in 2000 may be related to continued disturbance along the periphery of Macario Canyon. It is also possible that nearby Agua Hedionda Creek is a source for increased numbers of cowbirds in Macario Canyon. We recommend a review of recent trapping regimes in the vicinity of the project in order to understand the results of the cowbird trapping efforts in Macario Canyon and along Agua Hedionda Creek. We also compliment the City for having undertaken a major recommendation discussed in our 1999 report to increase the level of communication between the city, its contractors and biologists working in Macario Canyon. We encourage the continued level of communication between respective City staff and all -contractors working in the Macario/Agua Hedionda area. We found that it was extremely helpful and potentially of great benefit to protected species within our study area that coordination of activities and dissemination of pertinent information between contracting bodies, contractors, biological monitors, and resource agency representatives reduces the number of potential incidents that may harm protected species. In a development-rich zone such as Macario Canyon/Agua Hedionda Creek, the complexity of issues can grow exponentially. On site coordination between knowledgeable staff and field , experts from potentially impacted project sites will help facilitate the progress that is the focus of development while ensuring the protection afforded listed species. Unfortunately the U. S. Fish and Wildlife Service did not respond within an appropriate time period to our request to color band vireos in Macario Canyon. We reiterate that color marking of individual vireos will be of benefit to understanding the dynamics of this important restoration site. An understanding of the colonization process, habitat use, transience, construction impacts, as well as other important factors will help further the knowledge regarding the recovery of least Bell's vireo in southern California. Because the City of Carlsbad will continue to monitor the Final Report: Year 3, LBVi/WiFI Surveys 12 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 10 December 2000 ) I I vireo in Macario Canyon over the next two breeding seasons, we again this year recommend that I color banding of individuals augment the current level of study. A minimal investment in energy will greatly increase the value of data already being collected. I I I I . I I , I. I I I I Final Report: Year 3, LBVi/WiFl Surveys 13 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 10 December 2000 I REFERENCES Browning, M. R. 1993. Comments on the taxonomy of Empidonax traillii (Willow Flycatcher). Western Birds 24:241-257. Famolaro, Peter. 2000. Wildlife bilogist, Least Bell's vireo expert, Sweetwater Authority, Spring Valley, California. Personal communication. Hayes, Loren. 2000. Field Supervisor, Carlsbad Field Office, U. S. Fish and Wildlife Service, Carlsbad, California. Holland, D. C. 1986. Preliminary descriptions of the terrestrial natural communities of California. State of California Department of Fish and Game, Sacramento, California. Sogge, M.K.,R. M. Marshall, S. J. Sferra, and T. J. Tibbitts. 1997. A southwestern willow flycatcher natural history summary and survey protocol. Technical report NPS/NAUCPRSINRTR-97/12. National Park Service, Northern Arizona University, Colorado Plateau Research Station. Tetra Tech, Inc. 1995. Letter report to Ms. Sherri Howard, City of Carlsbad: Cannon Road Reach I least Bell's vireo surveys, Spring 1995. Tetra Tech, Inc. 1996. Letter report to Ms. Sherri Howard, City of Carlsbad: Cannon Road Reach I least Bell's vireo surveys, Spring 1996. U. S. Fish and Wildlife Service. 1995. Endangered and threatened wildlife and plants. Final I rule determining endangered status for the southwestern willow flycatcher. Federal Register 60:10694-10715. U. S. Fish and Wildlife Service. 1986. Endangered and threatened wildlife and plants. Final rule determining endangered status for the least Bell's vireo. Federal Register 51:16474- 16482. . U. S. Fish and Wildlife Service. 1998. Draft recovery plan for the least Bell's vireo. U.S. Fish I and Wildlife Service, Portland, OR. 139pp. I Unitt, P. 1987. Empidonax traillii extimus: an endangered subspecies. Western Birds. 18:137-162 Varanus Biological Services, Inc. 1998a. First annual report: 5-year Least Bell's Vireo and Willow Flycatcher Surveys and Monitoring Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. 8pp. I Varanus Biological Services, Inc. 1998b. First annual report: 5-year Brown-headed Cowbird Trapping Program, Cannon Road Extension Wetlands Mitigation Project, Macario I Final Report: Year 3, LBVi/WiFl Surveys 14 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 10 December 2000 I: Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. 8pp. Varanus Biological Services, Inc. 1999a. Second annual report: 5-year Least Bell's Vireo and Willow Flycatcher Surveys and Monitoring Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. Varanus Biological Services Inc. 1999b. Second annual report: 5-year Brown-headed cowbird trapping program, Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. lOpp. Yard, Helen K and Bryan T. Brown. 2000. Sexual and temporal differences in vocal behavior of nesting willow flycatchers along the Verde River, Arizona. Abstract from The Ecology and Conservation of the Willow Flycatcher Conference. 24-26 October 2000. Final Report: Year 3, LBVi/WiFl Surveys 15 Cannon Road Extension Wetlands Mitigation Project Varanus Biological Services 10 December 2000 Second Annual Report - 1999 Least Bell's Vireo and Willow Flycatcher Surveys and Monitoring Cannon Road Extension Wetland Mitigation Project Macario Canyon, Carlsbad, San Diego County, California City Project No. 3184 Report prepared for the City of Carlsbad Photo of Least bell's Vireo, Photograph by Anthony Mercieca Prepared by: Varanus Biological Services, Inc. 7950 Silverton Avenue, Suite 116 San Diego, CA 92126 Under Contract to: Native Landscape, Inc. 9746 Tamarack Escondido, CA 92029 I I INTRODUCTION Least Bell's vireos (Vireo bellii pusillus) have been documented as seasonal migrants and as a I potentially breeding species within Macario Canyon, a small north San Diego County, California riparian drainage that flows into Agua Hedionda Lagoon (Tetra Tech 1995). Between March and I September 1999, Varanus Biological Services (Varanus) conducted the second year of a five-year presence/absence survey for and nest monitoring of least Bell's vireo in Macario Canyon. Varanus conducted the surveys and nest monitoring in partial fulfillment of the City of I Carlsbad's (City) biological mitigation requirements for the Cannon Road Extension Project (Project) under terms agreed to as a result of Section 7 consultation with the U.S. Fish & Wildlife Service (FWS). Varanus conducted the vireo work between 15 March and 1 September 1999. I Willow flycatchers (Empidonax traillii ssp.) are also known to occur in the area as a migrant species (Tetra Tech 1996, Varanus 1998a). As an adjunct to the vireo work, Varanus also conducted presence/absence surveys for willow flycatcher in the project area. Willow flycatcher I surveys were not a component of the Project mitigation and not required by the resource agencies, however the City felt the surveys were warranted. Willow flycatcher survey protocols exceeded those currently recommended by the FWS (Sogge et al 1997), especially in that I Varanus conducted the surveys between 15 May and 15 August in association with the required weekly vireo censuses. I Least Bell's vireos are small migratory songbirds that are obligate summer residents of riparian habitat within Southern California and Northwestern Baja California, Mexico. Historically found throughout California from the northern Sacramento Valley south into Baja California, I populations of the least Bell's vireo suffered from extensive habitat destruction and brood parasitism from the brown-headed cowbird (Molothrus ater), especially between the 1940's and its subsequent listing as a protected species in the 1980's. The least Bell's vireo was listed as an I endangered species by the state of California in 1980 and became federally listed as an endangered species in 1986 (U.S. Fish and Wildlife Service 1986). Since its listing and subsequent recovery actions, U. S. populations of the least Bell's vireo have increased throughout I its range (U.S. Fish and Wildlife Service 1998). Willow flycatchers have been recognized taxonomically as at least four distinct sub-species or I races (Unitt 1987; Browning 1993). Of the four sub-species, only two are typically found in San Diego County: northwestern willow flycatcher (E. t. brewsteri), a relatively common migrant, I and southwestern willow flycatcher (E. t. extimus), a rare local breeding sub-species. Like Bell's vireo, willow flycatcher populations also declined in the latter part of the 20th century because of widespread habitat destruction and possibly also as a result of brood parasitism by brown-headed I cowbirds. As a result, the southwestern willow flycatcher was listed as an endangered species by the federal government (U.S. Fish and Wildlife Service 1995). Both northwestern and southwestern willow flycatchers are listed as endangered by the State of California. I Description of Study Area Macario Canyon is located in the northwestern portion of San Diego County. The canyon starts near the intersection of Faraday Avenue and College Boulevard in Carlsbad and waters carried by Draft Report: LBVi/WiFI 1 I Cannon Road Extension Varanus Biological Services I December 1998 I this small watershed flow northwest into the eastern edge of Agua Hedionda Lagoon (Figure 1). Approximately 250 acres in size, the study area is a mosaic of wetland and upland habitats composed primarily of Southern Cottonwood-willow Riparian Forest surrounded by non-native grasslands, agricultural fields, and disturbed Diegan Coastal Sage Scrub (Holland 1986). The upper (southern) reaches of the canyon are dominated by Southern Willow Scrub. Within the two major riparian habitats are patches of emergent riparian forest, freshwater marsh and baccharis scrub. Habitat quality varies and ranges from relatively undisturbed pockets of riparian forest to heavily disturbed and degraded areas that are subject to frequent human activity and are characterized by exotic plant species such as pampas grass (Cortaderia selloana) and tamarisk (Tamarix sp.). Dominant plant species within the study area are arroyo willow (Salix lasiolepis), Goodding's black willow (S. gooddingii), Fremont cottonwood (Populus fremontii), broom baccharis (Baccharis sarothroides) and cattail (Typha sp.). METHODS Least Bell's Vireo Varanus conducted 1999 surveys for least Bell's vireo on a weekly basis beginning 1 April and continuing until 1 September. Adult male least Bell's vireos are typically extremely vocal, especially upon or soon after arrival at their breeding grounds. Surveys for this species were conducted passively (that is, without assistance of pre-recorded tape playback or scolding ("spishing" or "pishing", etc.)) by slowly walking along suitable habitat, stopping every 50 meters to listen for vireos singing spontaneously. We generally conducted our surveys between 0700 and 1100 hours. Weekly surveys determined the locations of Macario Canyon vireos. We determined the number of vireos present in each territory, their breeding status and, when present, nest locations. Once found, nests were visited on a limited basis. Our nest visits focused on determination of number of eggs present and whether the nest had been parasitized, especially since cowbirds usually parasitize nests early in the laying phase. If found, cowbird eggs or young were removed. Thereafter, we monitored nests from a distance to minimize disturbance to both adult vireos and nestlings and to reduce potential for predators to detect nest locations. Typically a nest site was visited 3 times, with the first visit to establish the nest location and the number and type of eggs (specifically vireo or cowbird) present in the nest. The second visit, approximately a week later, was timed to determine whether the nest had been the target of cowbird activity. A third visit determined the age and number of nestlings. We confirmed nest success and number of fledges without further close approach to the nest. Ingri Quon or William Hans conducted the nest searches and monitoring. Willow Flycatcher Surveys for willow flycatcher followed survey protocols adopted by Region 1 of the USFWS (Sogge et a! 1997). Protocol surveys entail use of audio playback of pre-recorded willow flycatcher song while walking slowly along and within suitable willow flycatcher habitat. Three surveys are required by the protocol; the first between 15 and 30 May, the second between 1 and Draft Report: LBVi/WiFI 2 Cannon Road Extension Varanus Biological Services I December 1908 Figure 1. Vireo and Willow Flycatcher Locales, Macario Canyon, 1999 Macaiio Canyon Paired Least Bells Vireo Use Areas, 1999 Data 117°1851W WGS8411701728W z-ii' :y' '"j / ., ç • ._ / r o :b 60 60 C3 CD ' '; - ? r Willow Flycatcher summer use area, 1999 Least Bell's Vireo nest locations 1999 No . / 'i--- I \) Use area including terntory, Pair 99A -' lk i'h \ :rçr Cq 'c fan'kt 10. 1170151 W WGS84 117°1728 W TN/MN ? 1/2 1 MILE V ai,o 0 1000 FEET 0 500ii bOOm '? Printed from TOPO! ©1998 Wildflower Productions (www.tono.com Draft Report: LBVi/WiFI 3 Cannon Road Extension Varanus Biological Services 1 December 1998 21 June and a third between 22 June and 10 July. We conducted weekly surveys from 15 May through 15 August. All surveys were conducted between 0600 and 1000 hours. Protocol surveys have several limitations. Presence of singing willow flycatchers is only indicative of breeding or resident status. With current knowledge, it is impossible to distinguish between willow flycatcher subspecies by song alone. Also, presence of unmarked (that is, unbanded) individuals precludes determination that individuals observed during early season surveys are the same individuals present during later surveys. Moreover, the protocol focuses on elicited or spontaneous calls primarily of male willow flycatchers. Female willow flycatchers are known to elicit the prototypical "fitz-bew" or "fitz-a-bew" song, but do so less frequently. It has been our experience that migrating female willow flycatcher often respond to tape playback with a common but less well-recognized "whit." Even this is complicated by the fact that other Empidonax flycatchers, for example, dusky flycatcher (E. oberholseri) and gray flycatcher (E. wrightii), elicit a similar "whit" call. For these reasons, we extended our survey period and our surveys were augmented by additional observations of detected individuals to attempt to discern other behaviors and activities indicative of residency, especially nesting or other breeding activity. W. Hans conducted the willow flycatcher surveys. RESULTS Least Bell's Vireo Population Number and Distribution The first observation of least Bell's vireo in Macario Canyon in 1999 occurred on 1 May. This relatively late observation of first arrival in the canyon fits the general trend of late arrival observed throughout southern California this year (Pete Famolaro, Loren Hays personal communication, and Varanus personal observation). Although we conducted surveys on a weekly basis, Varanus cowbird trap monitor Tom Myers collected vireo data on a daily basis. Between 1 and 11 May, up to 5 adult vireos were observed or detected aurally within the canyon on a daily basis. On 11 May, the first acknowledged pair of vireos was observed in the vicinity of Varanus cowbird trap #4 (Figure 1). A total of 2 breeding pairs of vireos were detected within the study area during 1999. Distribution of vireo territories at the northern end of the canyon in 1999 was similar to those documented in 1996 by biologists Patrice Ashfield and Kim Miller (Tetra Tech 1996) and in 1998 by Varanus (Varanus 1998b). One 1999 vireo territory (Pair A_99) closely overlapped the territory established by one of the 1998 vireo pairs. This territory encompassed riparian habitat (including portions of the newly established North Mitigation Area) in the vicinity of Cowbird Trap #2. The second pair of vireos (Pair B_99) established a very large territory in the vicinity of Cowbird Traps #3 and #4, a shift in overall use area away from and upstream from the Cannon Road Extension Bridge construction area. At least three additional individuals, presumed to be migrant (sensu en route to breeding habitat at a more northerly locale) or transient (sensu searching for a territory in the near vicinity) adult males based on singing activity, were also detected within the study area. Female transients are typically Draft Report: LBVi/WiFI 4 Cannon Road Extension Varanus Biological Services I December 1998 more difficult to detect than males because of reduced singing activity and more discreet feeding behaviors. Transient females, therefore, may have passed through the study area undetected. Status of male vireos as migrants or transients was based on their presence in Macario Canyon for less than 14 days. Although unmarked, it appears that at least one male vireo lingered in the Canyon for approximately 14 days prior to departing. This individual was observed at the same location along Macario Creek on a daily basis for an entire two-week period. Territory A_99 Tom Myers, while tending cowbird traps on 1 May, detected the first Macario vireo of 1999. The individual was a vocal male foraging in the vicinity of Cowbird Trap #2. The apparently solitary male foraged in the creek bottom (older) riparian habitat but spent at least 12 minutes foraging in the recently planted Northern Mitigation Area. During the ensuing survey on 11 May, a solitary female vireo was found in the vicinity of Trap #2. The territory remained occupied by a solitary female until approximately 8 June when we detected a male and female vireo in the territory. The pair was observed within the territory through July 29th at which time the female was observed for the last time. The male of Pair A_99 was last observed on 13 August. The pair initiated nest building very late in the breeding season (7 July) but apparently failed to complete nest construction or deposit eggs. Territory B_99 On 1 May Myers also detected a singing vireo in the vicinity of Cowbird Traps #3 and #4. During the 4 May survey this (assumedly same) individual was observed for more than 30 minutes foraging over an extensive area that encompassed the west side of Macario Canyon between Cowbird Traps #3 and #5. On 11 May we observed a pair of vireos in the process of building a nest within a dense patch of coyote bush (Baccharis pilularis) in the vicinity of Cowbird Trap #4. On 2 June the female vireo appeared to be brooding eggs, however soon thereafter the nest was destroyed (ca. 5 June). Cause of the nest loss was undetermined. From 8 June through 6 July, only a male vireo was observed within Territory B_99. Difficulty conducting a scheduled survey on 6 July led to postponement of the survey until 10 July. On that date we found a completed nest with 2 eggs in the center of recent activity for the male vireo. The nest was located at the edge of a secluded opening characterized by freshwater marsh vegetation within a large expanse of taller, older willow riparian forest in the vicinity of Cowbird trap #4. The nest was built approximately 1 meter above the ground in an arroyo willow (Sal ix lasiolepis). On 15 July the nest contained 2, 5 or 6-day old vireo chicks indicating egg deposition occurred in late June (ca. 26 - 28 June). On 22 July we observed 2 recently fledged (1 —2 days old) young feeding with the adult male along the western edge of the Macario riparian habitat in the vicinity of Trap #4. We continued to find the adult male and two fledges in the vicinity of the natal territory through 20 August. At that time all three vireos divided time between the riparian edge and nearby upland habitat that included coyote bush, mustard (Brassica sp.), and several species of coastal sage vegetation. Draft Report: LBVi/WiFI Cannon Road Extension Varanus Biological Services 1 December 1998 5 I Banded Vireos No banded vireos were detected within the study area during 1999. Nest Success Nest success (that is, the percentage of completed nests that produced at least one fledgling) in 1999 was 33%. Pair A_99 attempted to nest without success on one occasion very late in the breeding season (nest construction occurred between 7 and 9 July). This nest was placed in an arroyo willow at the ecotone between the older riparian habitat along Macario Creek and the Northern Mitigation Area. Although built to near completion, there was no evidence of egg deposition. The nest was poorly attached to one branch of the willow and, even without the weight of a single egg, listed to one side. We detected no other nests within the Pair A99 territory, nor did we detect any behaviors indicating the presence of another nest. Pair B_99 constructed two (known) nests, the first placed in coyote bush and the second in arroyo willow. We documented a maximum of 3 eggs in the first of B_99's nests. The nest was located in a dense patch of coyote bush on the west side of Macario Creek in the vicinity of Cowbird Trap #4. The patch of coyote bush was located west of the access road approximately 20 feet from the nearby riparian habitat. The nest failed sometime between 2 and 5 June. On 4 June, Varanus' cowbird trap monitor T. Myers observed the male of Pair B_99 singing incessantly in upland habitat in the vicinity of its territory. This behavior reflected a change in behavior from what had been observed over the previous weeks. On the basis of Myers' observation the canyon was revisited on 5 June. The male was observed singing from the area described by Myers but the B_99 nest had been destroyed. Although not conclusively linked, this correlated to the occurrence of an unusual storm front accompanied by strong winds on the night of 3 June. The second nest of B_99 was constructed in an arroyo willow at the interior edge of a forest opening near Cowbird Trap #4. The nest site was located in the riparian vegetation within the Macario Creek channel. The nest was constructed approximately 1.1 meters above the ground at the edge of an opening characterized by freshwater marsh vegetation. When found on 28 June, the nest contained two eggs. On 22 July we observed 2 recently fledged young (estimated fledging date: between 20 and 22 July). At least one fledge was observed with the adult male during each ensuing survey through the 201h of August. Productivity A total of 5 eggs were observed in 3 monitored nests. Pair B_99 built two nests, the first with 3 eggs, the second with 2 eggs. A third nest, constructed by Pair A_99, was near completion however egg deposition was not documented or suspected, thus the average clutch size for known completed nests was 2.5 eggs per nest. Five of these eggs are known to have hatched resulting in a minimum of 2.5 nestlings per completed nest, a 100% hatching rate. Of the 5 nestlings, 2 (40%) are known to have survived to fledging. The reduced number of nest attempts in 1999 (n = 6 in 1998, n = 3 in 1999) may be correlated to the late arrival of vireos to their breeding grounds and a consequent shortened breeding season. Draft Report: LBVi/WiFl Cannon Road Extension Varanus Biological Services 1 December 1998 U LI Nest Site Characteristics Two plant species were utilized as nest substrate by Macario Canyon least Bell's vireo. Two of 3 nests (67%) were placed in arroyo willow. The remaining nest (33%) was placed in coyote bush. Nest heights ranged from 0.8 to 1.1 meters, with an average nest height of 1.0 meters. Both nests placed in arroyo willow were attached to y-shaped branches approximately 1 meter above the ground. The nest built within coyote bush was placed within several upward directed branches in the upper one-third of a densely leafed coyote bush in a coyote bush thicket. The only nest found for Pair A_99 was extraordinarily similar to one of two failed nests of Pair A in 1998. In each case the nests were attached to y-shaped branches approximately 1 meter above the ground. Each was attached along one side only, and in each case the nest ultimately fell to a position perpendicular to its original placement. In 1998 this resulted in the loss of three vireo nestlings within a day or two of fledging. In 1999, no eggs were deposited in the poorly attached nest. I Pair B_99's first nest was nestled within five adjoining branches of a coyote bush, being supported from below rather than being suspended from the branches to which it was attached. The latter condition is more typical for LBV. The second nest constructed by Pair I B_99 was attached to a y-shaped branch approximately 1 meter above the ground in an arroyo willow. The nest was approximately 0.5 meters from the edge of the tree along the periphery of a secluded area of freshwater marsh. Cowbird Parasitism Varanus conducted the second in a series of 5 consecutive seasons of brown-headed cowbird trapping in 1999. Varanus has operated a total of five cowbird traps each year. Cowbird trapping is concurrent with vireo surveys and monitoring (Varanus 1998a, 1999). Although cowbirds were detected in the study area throughout the breeding season, no incidents of brown-headed cowbird nest parasitism of least Bell's vireo were detected in Macario Canyon during 1999. The total number of cowbirds observed and captured was less in 1999 than in 1998. The decrease in number of cowbirds trapped may have been related to a shortened trapping period. However the amount of time spent in Macario Canyon did not differ significantly between 1998 and 1999. The number of cowbirds observed in Macario Canyon during 1999 was also fewer. Therefore the reduced number of captured cowbirds may reflect a reduction in overall numbers in the canyon during 1999. We did no tests nor did we conduct critical field studies to determine the causes of the apparent reduction in cowbird numbers in either year. Between 17 March and 24 July a total of 39 cowbirds (27 adult males, 9 adult females, and 3 juveniles) were removed (euthanized) from the canyon. Especially noteworthy was the decline in number of juvenile cowbirds captured and observed between 1998 and 1999 (3 in 1999 vs. 21 in 1998). In general the reduction in number of juvenile cowbirds corresponds to the reduced number of female cowbirds observed and captured during the 1999 field season. Draft Report: LBVi/WiFl Cannon Road Extension I Varanus Biological Services 1 December 1998 I L] I I I I I LII I I I I LI 7 Willow Flycatcher There has been no historic evidence that willow flycatchers breed in Macario Canyon, and there are no recent historic records indicating breeding behavior of willow flycatcher in the immediate area. Surveys in 1996 indicated the presence of migratory willow flycatchers on 7 June 1996 (Tetra Tech 1996). These were identified as "southwestern" willow flycatcher (E. t. extimus) however as with most migrants through San Diego County they were probably the more common "northwestern" willow flycatcher (E. t. brewsteri). Willow flycatchers were detected in Macario Canyon during surveys on 29 May and 5 June 1998. These observations correlated to a wave of willow flycatcher migration through San Diego County (Varanus 1998b). In 1999 willow flycatchers were again detected in migration. Despite the overall late arrival of many migrant species, we detected a minimum of 3 migrant adult willow flycatchers during a survey on 11 May. This is relatively early for migrants of this species to be passing through San Diego County in numbers. Between 1 and 3 willow flycatchers were observed each week from 11 May through early June, including a total of 3 presumed females (based on vocalization) on 8 June. On 23 June, after a lapse time between observations, we found 2 willow flycatchers in the general vicinity of vireo territory B_99. On 28 June only one flycatcher was found, again in the vicinity of the B_99 vireo territory. We observed no willow flycatchers in Macario Canyon between 28 June and 15 July, at which time an adult flycatcher was detected in the vicinity of the second nest of vireo PairB_99. This was the last date on which willow flS'catchers were observed in Macario Canyon in 1999. Based on the time period during which at least one flycatcher was observed in Macario Canyon, it is possible that the individual was an adult southwestern willow flycatcher. Site conditions in Macario Canyon, especially at the location frequented by between 1 and 2 flycatchers between 23 June and 15 July, are suitable to support nesting activity of this endangered species however nest searches this year proved negative. Difficulty in distinguishing between subspecies of the willow flycatcher precludes a definite identification of the individuals present in Macario Canyon in 1999. DISCUSSION I Breeding Success Least Bell's vireos have exhibited poor breeding success in Macario Canyon during recent years I (Tetra Tech 1996, Varanus 1998b). Two breeding pairs of vireo in Macario Canyon in 1998 failed to produce fledgling young. In 1999 only two fledged young resulted from three nesting attempts. Thus, while the existence of breeding vireos in Macario Canyon and their persistence is I an encouraging indication of its use as a potentially successful breeding site, there appear to be factors leading to reproductive failure. I One possible factor is the high degree of disturbance currently affecting Macario Canyon. Several projects (for example, Cannon Road Extension, Faraday Road Extension) have contributed to ongoing disturbance of vireo habitat or the habitat immediately adjacent to potential breeding I habitat. Vegetation removed in 1998 for the Cannon Road Extension Bridge removed some of Draft Report: LBVi/WiFI 8 ' Cannon Road Extension Varanus Biological Services 1 December 1998 I the highest quality riparian vegetation. Subsequently, one pair of vireos attempted to nest along the periphery of the disturbance. However this pair was unsuccessful in each of four nesting attempts. In 1999, a year in which nesting activity for many passerines in southern California was late and/or prolonged, construction activity for Faraday Road may have adversely impacted late season vireo activity in the northern portion of the canyon. As development in Macario Canyon proceeds, yearly monitoring will be able to document the effects of encroachment on the vireo population within the study area. Hopefully also, as the infrastructure surrounding Macario's riparian habitat is completed and disturbance to the native habitat within the canyon is reduced a larger and more stable vireo population will result. Habitat Restoration Initial inspection of the riparian restoration sites for the Cannon Road Extension Project mitigation located in Macario Canyon indicate overall vigor and suggest increased potential to support least Bell's vireo independent of surrounding development. The recently planted restoration sites have already provided habitat typically associated with least Bell's vireo colonization. If the existing territories (that is, the two territories documented in 1999) continue to support Bell's vireos, the new mitigation sites have the potential to provide for or to improve the quality of existing neighboring habitat to support at least 3 to 5 additional pairs of vireos. Restoration sites, planted in 1998 were used by foraging vireo in 1999, after only one year of growth. The sites may be suitable for breeding within two years (that is, by the year 2000). Concurrent trapping of brown-headed cowbirds will hopefully help offset potential adverse effects of recurrent nest and fledgling losses. However, this program will have little effect on adverse environmental activities, for example, housing development, road construction, use of the area by transients and migrant workers, and the probable increased ease of access to the northern portion of the canyon. Any of these activities may discourage vireo use of the area. We therefore suggest the following two broad recommendations be implemented at the Macario site: Coordination of Activities - The late breeding of least Bell's vireos documented throughout Southern California in 1999 presents a strong statement regarding the assignment of a definitive breeding season to species in general and specifically to protected species such as the vireo. In areas where construction activities may adversely impact breeding success of protected species and commencement of planned activities rest on the breeding status of those protected species, coordination must be enacted to maximize the exchange of information between contracting bodies, contractors, biological monitors, and resource agency representatives. In a development-riCh zone such as Macario Canyon/Agua Hedionda Creek, the complexity of issues can grow exponentially. On site coordination between knowledgeable staff and field experts from potentially impacted project sites will help facilitate the progress that is the focus of development while ensuring the protection afforded listed species. Identification Markers for Individual Vireos - The apparent increase in numbers of vireos Draft Report: LBVifWiFI Cannon Road Extension I Varanus Biological Services I December 1998 I 1 using Macario Canyon as both a migratory corridor and as a breeding site, along with the expansion in use area, including the regular use of a newly planted mitigation site by one pair I of vireos, suggests this is a very exciting area in which to study least Bell's vireo. An understanding of the colonization process, habitat use, transiency, construction, impacts, as well as other important factors will help further the knowledge regarding the recovery of least I Bell's vireo in southern California. Because the City of Carlsbad will continue to monitor the vireo in Macario Canyon over the next three breeding seasons, we recommend that the current level of study be augmented by color banding of individuals. A minimal investment I in energy will greatly increase the value of data already being collected. I I I I L] I 11~ I I I 1 I Draft Report: LBViIWiFl Cannon Road Extension Varanus Biological Services I December 1998 I F I REFERENCES Browning, M. R. 1993. Comments on the taxonomy of Empidonax traillii (Willow Flycatcher). I Western Birds 24:241-257. I Famolaro, Pete. 1999. Biologist, Sweetwater Authority. Personal communication, 15 April 1999. Hays, Loren. 1999. Biologist, U. S. Fish and Wildlife Service. Personal communication, 9 April I 1999. Holland, D. C. 1986. Preliminary descriptions of the terrestrial natural communities of I California. State of California Department of Fish and Game, Sacramento, California. Sogge, M.K., R. M. Marshall, S. J. Sferra, and T. J. Tibbitts. 1997. A southwestern willow .I flycatcher natural history summary and survey protocol. Technical report NPS/NAUCPRS/NRTR-97/12. National Park Service, Northern Arizona University, Colorado Plateau Research Station. I Tetra Tech, Inc. 1995. Letter report to Ms. Sherri Howard, City of Carlsbad: Cannon Road Reach I I least Bell's vireo surveys, Spring 1995. Tetra Tech, Inc. 1996. Letter report to Ms. Sherri Howard, City of Carlsbad: Cannon Road Reach I I least Bell's vireo surveys, Spring 1996. U. S. Fish and Wildlife Service. 1995. Endangered and threatened wildlife and plants. Final rule determining endangered status for the southwestern willow flycatcher. Federal I Register 60:10694-10715. U. S. Fish and Wildlife Service. 1986. Endangered and threatened wildlife and plants. Final rule I determining endangered status for the least Bell's vireo. Federal Register 51:16474- 16482. U. S. Fish and Wildlife Service. 1998. Draft recovery plan for the least Bell's vireo. U.S. Fish and Wildlife Service, Portland, OR. 139pp. I Unitt, P. 1987. Empidonax traillii extimus: an endangered subspecies. Western Birds. 18:137-162 I Varanus Biological Services, Inc. 1998a. First annual report: 5-year Brown-headed Cowbird Trapping Program, Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of I Carlsbad, City Project No. 3184. 8pp. Varanus Biological Services, Inc. 1998b. First annual report: 5-year Least Bell's Vireo and I Willow Flycatcher Surveys and Monitoring Cannon Road Extension Wetlands Mitigation Draft Report: LBVi/WiFl 11 I Cannon Road Extension Varanus Biological Services I December 1998 I Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. 8pp. Vararius Biological Services Inc. 1999. Second annual report: 5-year Brown-headed cowbird trapping program, Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184. 9pp. Draft Report: LBVi/WIFI 12 Cannon Road Extension Varanus Biological Services 1 December 1998 First Annual Report - 1998 Least Bell's Vireo and Willow Flycatcher Surveys and Monitoring Cannon Road Extension Wetland Mitigation Project Macario Canyon, Carlsbad, San Diego County, California City Project No. 3184 Report Prepared for the City of Carlsbad Prepared by: Varanus Biological Services, Inc. 7950 Silverton Avenue, Suite 116 San Diego, CA 92126 Under Contract to: Native Landscape, Inc. 9746 Tamarack Escondido, CA 92029 S INTRODUCTION As part of the City of Carlsbad's biological mitigation requirements for the Cannon Road Extension Project (Project) under terms agreed to as a result of Section 7 consultation with the U.S. Fish & Wildlife Service (USFWS). Varanus Biological Services (Varanus) conducted the first year of a five year presence/absence and nest monitoring survey for least Bell's vireo ( Vireo belliipusillus) between 15 March and 15 August 1998 in Macario Canyon, Carlsbad, San Diego County, California. As an adjunct to this effort, although not required by resource agency conditions, Varanus.also conducted protocol presence/absence surveys for willow flycatcher (Empidonax traillii ssp.) in the project area between 15 May and 20 July (Sogge eta! 1997). Least Bell's vireo have been documented to breed within the canyon, albeit with little success. Surveys in 1995 revealed a pair of vireo feeding ajuvenile (Tetra Tech 1995). Willow flycatchers are also known to occur in the area as a migrant species (Tetra Tech 1996). There are no indications that willow flycatcher nest in Macario Canyon. Data collected during the 1998 field (breeding) season corroborate results of earlier studies. Least Bell's vireos are small migratory songbirds that are obligate summer residents of riparian habitat within Southern California and Northwestern Baja California, Mexico. Historically found throughout California from the northern Sacramento Valley south into Baja California, the least Bell's vireo suffered from extensive habitat destruction and brood parasitism from the brown-headed cowbird (Molothrus ater), especially between the 1940's and its subsequent listing as a protected species in the 1980's. The least Bell's vireo was listed as an endangered species by the state of California in 1980 and became federally listed as an endangered species in 1986 (U.S. Fish and Wildlife Service 1986). Since its listing and subsequent recovery actions, numbers of least Bell's vireo have increased throughout its range (U.S. Fish and Wildlife Service 1998). Willow flycatchers have been taxonomically recognized as at least four distinct sub-species or races (Unitt 1987; Browning 1993). Of the four sub-species, only two are typically found in San Diego County: northwestern willow flycatcher (E. t. brewsieri), a relatively common migrant and southwestern willow flycatcher (E. t. extimus), a rare local breeding sub-species. Like Bell's vireo, willow flycatcher populations also declined in the latter part of the 20th century because of widespread habitat destruction and brood parasitism by brown-headed cowbird. As a result, the southwestern willow flycatcher was listed as an endangered species by the federal government (U.S. Fish and Wildlife Service 1995). Both northwestern (E. t. brewsteri) and southwestern (E. t. extimus) willow flycatchers are listed as endangered by the State of California. Description of Study Area Macario Canyon is located in the northwestern portion of San Diego County. The canyon starts at the west terminus of Faraday Avenue in Carlsbad and flows northwest into the eastern edge of Agua Hedionda Lagoon (Figure 1). Approximately 250 acres in size, the study area is a mosaic of wetland and upland habitats composed primarily of Southern Cottonwood-willow Riparian Forest located adjacent to agricultural slopes and disturbed Diegan Coastal Sage Scrub (Holland 1986). The upper (southern) reaches of the canyon are dominated by Southern Willow Scrub. Within the two major riparian habitats are patches of emergent riparian forest, freshwater marsh and baccharis scrub. Habitat quality varies and ranges from relatively undisturbed pockets of riparian forest to heavily disturbed and degraded areas that are subject to frequent human activity and are characterized by exotic plant species such as pampas grass (Cortaderia selloana) and tamarisk (Tamarix sp.) establishment. Dominant plant species within the Draft Report: LBVI/WiFI Cannon Road Extension Varanus Biological Services I December 1998 rap #41 - :. 33°0732' 117°1743" I MILE DC 3000 4000 FEET FIGURE 1 1998 LEAST BELL'S VIREO NEST LOCATIONS MACARIO CANYON, CARLSBAD, CALIFORNIA 33°0824. 117*19or 330824' 117°174r ILBVi Pair #1, Nest #2 LBViPaar#1 Nest#lr - IBHC1 I LB Vi Pai ILBVi Nest I .UIBHC0 TTh.QI 33°0732, 117°190r TNlMN L I/iiiio 1000 F, I V Printed ftm TOPOI 01997 Wildfwer Productions (www.topo.com) Draft Report: LBVI/WiFl Cannon Road Extension Varanus Biological Services 1 December 1998 2 study area are arroyo willow (Sal ix lasiolepis), Goodding's black willow (S. gooddingii), Fremont cottonwood (Populusfremontii), broom baccharis (Baccharis sarothroides) and cattail (Typha sp.). METHODS Least Bell's Vireo Varanus conducted initial 1998 surveys for least Bell's vireo on a daily basis concurrent with general avian monitoring and nest searches associated with other grading activities for the project wetland mitigation site and Cannon Road Bridge abutment commencing 15 March until 30 March. Adult male least Bell's vireos are typically extremely vocal, especially upon arrival at their breeding grounds. Surveys for this species were conducted passively (that is, without assistance of pre-recorded tape playback or scolding ("spishing" or "pishing", etc.) by slowly walking along suitable habitat, stopping every 50 meters to listen for spontaneous singing of vireos. Surveys were conducted between 0700 and 1100 hours. Varanus changed to weekly surveys beginning 30 March until 30 April at which time "surveys" were incorporated into weekly nest monitoring and post-breeding surveys that continued until 1 September. Weekly surveys determined the location and breeding status of Macario Canyon vireos. Nest site visits were limited to minimize disturbance to both adult vireos and nestlings, and to reduce potential for predators to detect nest locations. Typically a nest site was visited 3 times, with the first visit to establish the nest location and number of eggs. The second visit was timed to determine the age and number of nestlings and a final visit to confirm nest success and number of fledges. Each nest visit was designed to minimize impacts to both vireo nest and nest substrate. Ingri Quon and William Haas conducted nest searches and monitoring. Willow Flycatcher Surveys for willow flycatcher followed survey protocols adopted by Region I of the USFWS (Sogge et al 1997). Protocol surveys entail use of audio playback of pre-recorded willow flycatcher song while walking slowly along and within suitable willow flycatcher habitat. Three surveys are required by the protocol; the first between 15 and 30 May, the second between I and 21 June and a third between 22 June and 10 July. We conducted four surveys; on 29 May, 5 June, 19 June and 2 July. All surveys were conducted between 0600 and 1000 hours. Protocol surveys have several limitations. Presence of singing willow flycatchers is only indicative of potential resident status. With current knowledge, it is impossible to distinguish between willow flycatcher subspecies by song alone. Also, presence of unmarked (that is, unbanded) individuals precludes determination that individuals observed during early surveys are the same individuals present during later surveys. Moreover, the protocol focuses on elicited or spontaneous calls primarily of male willow flycatchers. Female willow flycatchers are known to elicit the prototypical "fitz-bew" or "fitz-a-bew" song, but do so less frequently. It has been our experience that migrating female willow flycatcher often respond to tape playback with a common but less well-recognized "whit." Even this is complicated by the fact that other Empidonax flycatchers, for example, dusky flycatcher (E. oberholseri) and gray flycatcher (E. wrightii), elicit a similar "whit" call. For these reasons, our surveys were augmented by additional observations of detected individuals to attempt to discern other behaviors and activities indicating evidence of residency, especially nesting or other breeding activity. W. Haas conducted willow flycatcher surveys. Draft Report: LBViIWiFl Cannon Road Extension Varanus Biological Services 1 December 1998 RESULTS Least Bell's Vireo Population Number and Distribution The first observation of least Bell's vireo in Macario Canyon in 1998 occurred on 15 April. On 17 April, the first acknowledged pair of vireos was observed in the vicinity of Varanus cowbird trap #1 (Figure 1). Two breeding pairs of vireo were detected within the study area during 1998 surveys and nest monitoring. Two additional individuals, presumed to be migrant adult male least Bell's vireo based on singing activity, were also detected within the study area. Female transients are typically more difficult to detect because of reduced singing activity and more discreet feeding behaviors. Transient males were determined to be present for less than 30 days and were probably birds passing through the study area in migration. Transient females may have been overlooked. Overall distribution of vireo territories at the northern end of the canyon in 1998 was similar to those documented in 1996 by biologists Patrice Ashfield and Kim Miller (Tetra Tech 1996). Vireo territories were located in close proximity to or within older, more established riparian habitat, located in this end of the canyon. Both pairs of vireo detected during 1998 favored this maturer riparian habitat for nest site selection (Figure 1). Pair A attempted a total of four nests. Each was located north of the area cleared for construction of the Cannon Road Bridge abutment. The first nest attempt involved a completed nest with three eggs and was located along the western edge of the riparian habitat in coyote bush (Baccharis pilularis). This nest was apparently destroyed by an unseasonably late storm during the first week of May. The nest was extremely well camouflaged and there was no evidence of close approach by humans or other predators. Remnants of two of the three eggs were found on 14 May directly under the nest. Two subsequent nest attempts, both in black willow due north of the cleared abutment area, were abandoned prior to completion. A fourth nest was constructed in a small thicket of Southern Willow Scrub north of the project area. This last nest was completed and three eggs deposited by 5 June. The female of this pair was observed on the nest on 11 June, but was not disturbed. Our survey on 18 June found the nest abandoned and the eggs missing. Neither individual from this pair was observed in Macario Canyon after this date. Pair B attempted a total of two nests, both of which failed just prior to the fledging of young. Both nests were located in the area south of territories used by Pair A, between the San Diego Gas and Electric access road and the newly planted northern restoration site in the vicinity of cowbird trap #2 (Figure 1). Both nests were constructed at the interface between riparian forest and freshwater marsh; each nest was placed in arroyo willow. All evidence indicates Pair B's first nest failed just prior to fledging of three young. We noted from the beginning of our observations that this nest was suspended in a very precarious position. The nest was attached to a single willow branch and suspended from just one side. On 11 June, our survey found the nest perpendicular to the ground, covered with Argentine ants (Iridomyrmex humilis). It is possible that one or more young fledged prior to the nest having assumed a position perpendicular to the ground. However, the 11 June survey did not detect fledgling vireo, nor were any behaviors indicating parental care of young observed. It is therefore more likely that the weight of the three nestlings as they approached fledging size caused the nest to torque on its axis of attachment and the open cup nest would have spilled its contents to the ground. Flightless, the young may have become easy prey to any number of predators including long-tailed weasel (Mustelafrenata), non-native rats (Rattus spp:), and Argentine ants. Pair B's second nest contained two eggs when discovered on 18 June. Least Bell's vireos rarely begin nest construction and egg deposition in the first two weeks after Draft Report: LBViJWiFI Cannon Road Extension Varanus Biological Services 1 December 1998 fledging if the young survive. This is further evidence that Pair B's first nest ended in failure. Pair B's second nest was placed in a very similar situation to its first nest. The second nest was fastened more securely, this time attached and hanging between two branches of an arroyo willow approximately one meter above the ground. Two eggs were found in the nest on 19 June and the female observed sitting on the nest during our 26 June survey. She was not disturbed at that time. The nest was again observed from a distance on 2 July at which time one of the vireo adults was observed bringing food to and feeding young in the nest. A nest check on 6 July revealed the nest to have been destroyed. There was insufficient evidence to suggest a cause for the nest destruction. Subsequent surveys indicated no further breeding activity by this pair. During the 6 July visit it was noted that the male of Pair B had begun its pre-basic molt, a good indicator of breeding cycle end. Although the male of Pair B was observed on three subsequent surveys (on 10, 16 and 24 July), the female was last observed on 6 July. Banded Adult Vireos We observed no banded vireos within the study area during 1998. Nest Success Nest success in 1998 was zero. Pair A attempted to nest four times and Pair B attempted to nest two times. All nest attempts were unsuccessful. One nest attempt (nest #1 of Pair A) appears to have been destroyed by inclement weather. Two nests (nests #2 and #3 of Pair A) were abandoned prior to egg deposition. Causes for abandonment are unknown. One nest (nest #1 of Pair B) was unsuccessful, probably due to poor nest placement. A thorough investigation of the vicinity of Pair A's fourth nest was inconclusive. The nest was intact and there was no evidence of eggs, remnant eggshells, young (including skeletonized young) or adults. No distinguishable footprints (human or non-human) were found in the area surrounding the nest. No other evidence of depredation was detected. The second and final nest of Pair B was destroyed and its contents assumedly depredated. A thorough search of the area revealed no remains of the two nestlings. Both adults, however, were observed in the vicinity of the destroyed nest. Productivity A total of 11 eggs were observed in 6 nests (4 completed nests) which were monitored from the onset of incubation. The average clutch size was 2.75 eggs per completed nest. Five of 11(45%) of these eggs are known to have hatched resulting in a minimum of 1.25 nestlings per completed nest. The disposition of three eggs (deposited in nest #4 of Pair A) is unknown. Of the 5 nestlings, none (0%) are known to have survived to fledge. It is, however, possible that one or more nestlings from Pair B's first nest survived to fledging and then succumbed to depredation or other demise (for example, starvation) soon after leaving the nest. Nest Site Characteristics Two plant species were utilized as nest substrate by Macario Canyon least Bell's vireo. Five of 6 nest attempts (83%) were placed in arroyo willow. The remaining nest was placed in coyote bush. Nest height ranged from 1.0 to 1.8 meters, with an average nest height of 1 .I meters. All but one nest placed in arroyo willow (the failed nest #1 of Pair B) were attached to y-shaped branches approximately 1 meter above the ground. Pair B's first nest was attached on one side (to one branch) only and ultimately fell to a position perpendicular to its original placement. Pair A's first nest was nestled within five adjoining branches of a coyote bush, being supported from below more so than being suspended from the branches to which it was attached. Draft Report: LBViIWiFI Cannon Road Extension Varanus Biological Services I December 1998 Cowbird Parasitism No incidents of nest parasitism of least Bell's vireo were detected in Macario Canyon during 1998 although cowbirds were detected in the study area throughout the breeding season. Total numbers of cowbirds observed, however, were greatly reduced in July and August. Varanus conducted cowbird trapping during this time period concurrent with vireo surveys and monitoring (Varanus 1998). A total of five cowbird traps were operated for the entire vireo breeding season (late March through August). Between 20 March and 25 August, a total of 78 cowbirds (30 adult males, 27 adult females, and 21 juveniles) were removed from the canyon. Willow Flycatcher There is no evidence that willow flycatchers reside in Macario Canyon, nor are there historic records indicating breeding behavior of willow flycatcher in the immediate area. Surveys in 1996 indicated the presence of migrating willow flycatcher on 7 June (Tetra Tech 1996). These were identified as "southwestern" willow flycatcher (extimus). Most migrants through San Diego County are the more common "northwestern" willow flycatcher (brewsteri). Due to the difficulty distinguishing the two sub- species in the field especially during the migration period it is recommended that the 1996 records be considered willow flycatchers of unidentified subspecies. Willow flycatchers were again detected in Macario Canyon during surveys on 29 May and 5 June 1998. Two singing individuals were detected during the 29 May survey and one individual was detected during the 5 June survey. No willow flycatchers were detected during subsequent surveys on 19 June or 2 July; during weekly monitoring of least Bell's vireo; or during cowbird trap maintenance. All of the 1998 Macario sightings coincided with a widespread migratory wave of willow flycatcher through San Diego County. Additional nearby sightings included 3 individuals detected on 10 June and a single, probable female willow flycatcher found on 11 June by W. Haas and I. Quon along Agua Hedionda Creek. DISCUSSION Least Bells' vireos have exhibited poor breeding success in Macario Canyon during recent years. Two breeding pairs of vireo in Macario Canyon in 1998 failed to produce fledgling young. All nest attempts were unsuccessful. The existence of breeding vireos in Macario Canyon and their persistence is an encouraging indication of its potential future use as a breeding site. However, in addition to reproductive failure in 1998, several problems face this small vireo population. These include the proposed residential and recreational development of the slopes surrounding Macario Canyon and nearby Agua Hedionda Creek. As development in the area proceeds, yearly monitoring will be able to document the effects of encroachment on the vireo population within the study area. Initial inspection of the riparian restoration sites for Cannon Road Extension Project mitigation located in Macario Canyon indicate overall vigor and suggest increased potential to support least Bell's vireo independent of surrounding development.. The recently planted restoration sites will provide habitat typically associated with least Bell's vireo colonization. Restoration sites, planted in 1998 should be usable by foraging vireo in 1999, after only one year of growth. The site may be suitable for breeding within two years (that is, by the year 2000). Concurrent trapping of brown-headed cowbirds will hopefully help offset potential adverse effects of recurrent nest and fledgling losses. However, this program will have little effect on adverse environmental activities that may discourage vireo use of the area, for example, housing development, Draft Report: LBVi/WiFl Cannon Road Extension Varanus Biological Services I December 1998 road construction, use of the area by transients and migrant workers and probable increased ease of access to the northern portion of the canyon. Draft Report: LBVi/WiFI Cannon Road Extension Varanus Biological Services I December 1998 S S References Browning, M. R. 1993. Comments on the taxonomy of Empidonax traillii (Willow Flycatcher). Western Birds 24:241-257. Holland, D. C. 1986. Preliminary descriptions of the terrestrial natural communities of California. State of California Department of Fish and Game, Sacramento, California. Sogge, M.K., R. M. Marshall, S. J. Sferra, and T. J. Tibbitts. 1997. A southwestern willow flycatcher natural history summary and survey protocol. Technical report NPS/NAUCPRS/NRTR-97/12. National park Service, Northern Arizona University,Colorado Plateau Research Station. Tetra Tech, Inc. 1996. Letter report to Ms. Sherri Howard, City of Carlsbad: Cannon Road Reach I least Bell's vireo surveys, Spring 1996. Tetra Tech, Inc. 1995. Letter report to Ms. Sherri Howard, City of Carlsbad: Cannon Road Reach I least Bell's vireo surveys, Spring 1995. U. S. Fish and Wildlife Service. 1998. Draft recovery plan for the least Bell's vireo. U.S. Fish and Wildlife Service, Portland, OR. I39pp. U. S. Fish and Wildlife Service. 1995. Endangered and threatened wildlife and plants. Final rule determining endangered status for the southwestern willow flycatcher. Federal Register 60:10694-10715. U. S. Fish and Wildlife Service. 1986. Endangered and threatened wildlife and plants. Final rule determining endangered status for the least Bell's vireo. Federal Register 51:16474-16482. Unitt, P.1987. Empidonax traillii extimus: an endangered subspecies. Western Birds. 18:137-162 Varanus Biological Services. 1998. First annual report: 5-year Brown-headed Cowbird Trapping Program, Cannon Road Extension Wetlands Mitigation Project, Macario Canyon, Carlsbad, San Diego County, California. Report prepared for the City of Carlsbad, City Project No. 3184.8pp. Draft Report: LBVi/WiFl Cannon Road Extension Varanus Biological Services 1 December 1998