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HomeMy WebLinkAbout3184; CANNON ROAD WEST; 5-YEAR BROWN-HEADED COWBIRD TRAPPING PROGRAM; 2002-11-01M/ ~ Final Report 5-year Brown-headed Cowbird Trapping Program Cannon Road Extension Wetlands Mitigation Project Macario Canyon, Carlsbad, San Diego County, California City Project No. 3184 Report Prepared for the City of Carlsbad I Report Prepared By: Varanus'Biological Services, Inc. 7920 Silverton Avenue, Suite D 1 San Diego, CA 92126 Under Contract to: I .Native Landscape, Inc. 9746 Tamarack Lane Escondido, CA 92029 Principal Investigator: William E. Haas 1 November 2002 RECEIVED JAN 0 9'2003 ENGINEERING DEPARTAREW INTRODUCTION The City of Carlsbad was required to implement a brown-headed cowbird (Molothrus ater, BHCO) trapping program in Macario Canyon. This program was part of the biological mitigation for the Cannon Road Extension Project, under terms agreed to as a result of Section 7 consultation with the U.S. Fish & Wildlife Service (FWS, Biological Opinion No. 1-6-97-F-51). The focus trapping area for the program was the north end of Macario Canyon, Carlsbad, San Diego County, California. The canyon is characterized by hillsides of native Coastal Sage Scrub and agricultural fields. Natural drainage and runoff from upstream development and from the adjacent agricultural fields is sufficient to support Southern Willow Scrub and Southern Cottonwood-willow Riparian Forest habitats along the bottom of the canyon. Drainage from Macario Canyon flows northward into Agua Hedionda Lagoon. Varanus conducted this cowbird-trapping program in support of recovery of the least Bell's vireo (Vireo bell/i pusilius), a federally listed endangered species. Least Bell's vireos are small, insectivorous, migratory songbirds of extremely limited range. Wintering in Baja California, Mexico, least Bell's vireos typically migrate northward to their breeding grounds in southern California between mid-March and mid-April. They breed almost exclusively in early succession willow-riparian habitats characterized by the presence of dense understory vegetation. Other nesting habitat includes dense patches of herbaceous understory in Coast Live Oak Riparian Forest and Coast Live Oak Woodland, and occasionally in patches of non-native habitat that now commonly form intricate mosaics with native habitats throughout the coastal breeding range of this species. Natural History of the Least Bell's Vireo and Brown-headed Cowbird Once widespread in low-elevation riparian valleys as far north as Tehama County in northern California, least Bell's vireo population numbers declined dramatically between the 1940's and mid-1980's (U. S. Fish and Wildlife Service 1986). Two factors are primarily responsible for this species' demise and hence have contributed to its status as an endangered species: Habitat loss resulting from eradication, fragmentation and degradation of southern California riparian corridors, and brood parasitism by brown-headed cowbirds (U.S. Fish and Wildlife Service 1998). The explosive increase in brown-headed cowbird numbers outside their Fifth Annual Report -2002 1 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 November 2002 historic range has accompanied the decline of riparian habitat. Habitat fragmentation leading to increased forest edge and the presence of domestic livestock are two modifications that increase the likelihood of cowbird parasitism (Ortega 1998). In southern California, the increase in brown- headed cowbirds has also paralleled the decline in San Diego County of numerous songbird populations including the yellow warbler (Dendroica petechia) and the warbling vireo (Vireo gilvus) (Unitt 1984). It is probable that subsequent brown-headed cowbird trapping has conversely brought about recent San Diego County increases in affected populations of riparian species (Robinson et al 1993) such as the yellow-breasted chat (Icteria virens), the yellow warbler, and the Bell's vireo (Philip Unitt personal communication). Brown-headed cowbirds were historically associated with buffalo and possibly, antelope herds, and subsequently livestock in the Great Plains of the United States (Weidensaul 1991). It is hypothesized that brood parasitism in brown-headed cowbirds evolved to accommodate the species' reliance on benefits gained foraging among herds of nomadic hoofed mammals (lb/cl). When, as it is postulated, nomadic herds moved, brown-headed cowbirds followed suit. Female brown-headed cowbirds that deposited eggs in other species' nests had the potential to achieve "nest success" at the expense of parasitized hosts. This also allowed the cowbirds to move en masse with the herds and to take advantage of a ready source of concentrated food resources (insects and seeds associated with ungulate feces). Female cowbirds that tended their own nests would thus sacrifice the safety in numbers afforded this social species when in association with large ungulate herds, and the availability of readily accessible forage. Over time the parasitic behavior was sufficiently advantageous to become a primary breeding strategy. Once incorporated into the behavior genome, it rapidly overwhelmed the traditional breeding system because it afforded extreme mobility to each female and the potential to annually deposit large numbers of eggs into surrogate nests. Nest success could be thus achieved with minimal investment in brooding, feeding and otherwise caring for young. Brown-headed cowbirds have been documented using more than 200 bird species as hosts (for example, Friedmann et al 1977). Brood parasitism of the least Bell's vireo by brown-headed cowbirds has been well documented. The history of cowbird/least Bell's vireo interaction is summarized in Franzreb (1989). Trapping of brown-headed cowbirds using modified Australian Crow Traps is an accepted method of reducing brood parasitism in least Bell's vireo (Ibid.) and other riparian (for example, Fifth Annual Report - 2002 2 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 November 2002 I I the black-capped vireo (Vireo atricapillus) (for example, Hayden et a! 2000) and non-riparian I species (for example, the California gnatcatcher (Polioptila calfornica) (for example, Braden et a! 1997). Cowbird trapping (and removal), and habitat restoration and preservation have been I associated with recent population recovery in parts of the least Bell's vireo's historicrange (U.S. Fish and Wildlife Service 1998). I METHODS I Varanus Biological Services, Inc. (Varanus), under contract to Native Landscape, Inc., was responsible for implementing a five-year cowbird-trapping program in Macario Canyon for the City of Carlsbad. Cowbird trapping was performed under authorization issued to Varanus from both the FWS and California Department of Fish & Game (CDFG) (Appendix A). The I contract specified deploying a total of five traps (2002 locations, Figure 1). Varanus acquired bait birds from traps at the Hollandia Dairy, San Marcos, San Diego County. Activity and song of I "caged" (= bait) cowbirds (that is, cowbirds placed in the modified Australian crow traps) attract targeted free-flying cowbirds. Birds captured at the dairy were used as "bait" birds in the five I traps. In 2002 we deployed our five traps in Macario Canyon on 15 March, and completed the I trapping regime on 16 July. Varanus maintained the cowbird traps in accordance with FWS- and CDFG-required protocols (Griffith Wildlife Biology 1994). To maximize effectiveness, we I activated each cowbird trap with five cowbirds and supplied each trap with water and seed. We also posted laminated signs on the trap that describe, in English and Spanish, the purpose and techniques of cowbird trapping as well as a contact number in case of problems or questions. Following activation, we checked the traps daily to wing clip and/or remove newly captured cowbirds (especially females) and to release non-target species. Wing clipping (that is, cutting wing feathers to hinder flight capabilities) all captured target cowbirds hinders predator avoidance by escaped cowbirds in addition to allowing determination of which birds are newly caught (that is, by distinguishing those with unclipped wings). By removing and euthanizing female cowbirds upon capture we also reduced potential escapee-caused nest parasitism within the habitat where we conducted the focused trapping. We daily removed females in the event that vandalism occurred allowing brown-headed Fifth Annual Report -2002 . 3 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 November 2002 cowbirds to escape, thus minimizing the potential for females to parasitize even nearby passerine nests. During each daily visit we added fresh seed and water if required, and cleaned seed pans and water dispensers when necessary. To minimize trap entry by non-target species we used white millet (Panicum miliaceum). Although relatively expensive, our seed choice does not contain an assortment of other seed types, such as sunflower seeds, that are attractive to many potential non-target species (for example, house finches, (Carpodacus mexicanus)) (Rosenberg and Bonney 1994). FA 0 C., Iv) C') S 1WtrIMN 'i— -. - ---- - II13" .ow go 9 I Map rarated with TOPO!@ @2002 N I' m1Geogzaphi (wwwthadocomftopo) Figure 1: 2002 Brown-headed Cowbird Trap Locations Macario'Canyon, Carlsbad,' California - RESULTS Brown-headed Cowbird From 1998 through 2002, we captured a total of 322 BHCO in Macaro Canyon. Of these, 170 were males, 86 were females and 66 were juveniles (Table 1). 1998, 2000 and 2001 were the most successful years for trapping with 83, 81, and 79 captures, respectively. No clear pattern of declining numbers of adult cowbirds was evident during this trapping program (Figure Filth Annual Repod - 2002 . 4 5-year Brown-headed COWbInI Trapping Program Varanus Biological Services, Inc. 1 dn,,hs.')flft) , 2). The number of juveniles captured each year declined from 2000 to 2001 and from 2001 to 2002 with 25, 14 and 2 captures, respectively. Daily captures of target and non-targets are listed in Appendix B. Table 1. Brown-headed cowbird trapping results for Macario Canyon, Carlsbad, California 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 1 or unaccounted for depredation. 4 5 6 3 19 BHCO removed from Macario Canyon and euthanized 82 41 76 63 29 301 In our five-year program, captures of adult male BHCO occurred in every month except August (Figure 3). The highest number of female captures occurred during March, April and May. The majority of juveniles were captured in June and July. We recorded no incidents of vandalism during any year of the trapping program. During several years we lost relatively large numbers of cowbirds to in-trap depredation (118 in 2001 and again in 2002). We have determined that long-tailed weasel (Mustelafrenata), Cooper's hawk (Accipiter cooperii), and sharp-shinned hawk (Accipiter striatus) caused cowbird mortality within traps at Macario Canyon. We captured one sharp-shinned hawk in a trap that had killed and eaten seven cowbirds in its one-day visit. We have observed Cooper's hawks "working" the BHCO traps by scaring trapped cowbirds from the bottom into the apical upper corners of several traps, grabbing the cornered birds with talons, and then decapitating them. Cooper's hawks may succeed in removing the head only, or may be able to pull the entire carcass through the wire mesh leaving telltale feathers attached to the wire grid. They may also extract fallen carcasses if the deceased cowbird falls sufficiently close to a bottom edge of the trap. Fifth Annual Report - 2002 5 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 November 2002 i - I, -'p I I, • '•, At 'l ••,..-- 'i' - ' I-- - Figure 3: Total BHCO Captures by Month for Macarlo Canyon, Carlsbad, San Diego . County ' - '5 Filth Annual Report 2002 6 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. I !,J.s.,..niw1flfl1 . S •s, is DMales 68 flFemates - OJuveniles 41 ________ ________ ______________ _________________________ 5'__ •1 39 21 18 ' : 12 Lii • : I I 50- 45- 40- 2 35 V - 3 30 25- 2 20- E 3 z 15- 10- 5- 1998 - 1999 2000 2001 2002 Year OMales 0 Females 1; I. •• ii. i• - F I• .•_ .- ii I• - II. ui.I__- U I iu •uui' ••• .u•uIu II 0-1 Figure 2: Total BHCO Captures Macario Canyon, Carlsbad, San Diego County I Non-target Species We recorded a total of 1,620 non-target bird (that is, non-BHCO) captures in Macario Canyon cowbird traps (Table 2). Song sparrow (Melospiza melodia) was the most frequently trapped non-target species, followed by California towhee (Pipilo crissalis) (Figure 4). Other species captured include the house finch, western scrub-jay (Aphelocoma calfornica), red- winged blackbird (Agelaius phoeniceus), spotted towhee (Pipilo maculatus), California thrasher (Toxostoma redivivum), house sparrow (Passer domesticus), black phoebe (Sayornis nigricans) and sharp-shinned hawk. Non-target mortalities were limited to 19 individuals with California towhees composing the majority of the losses. The percent mortality was 1.17%. Table 2. Non-target species captured During Cowbird Trapping Macario Canyon, Carlsbad, California Total trapped (Deceased) 1998 1999 2000 2001 2002 All Years House sparrow 0 (0) 0 (0) 4 (0) 0 (0) 0 (0) 4 (0) Song sparrow 84 (0) 13 (0) 43 (0) 330(l) 357 (0) 827 (1) California towhee 66 (4) 104(0). 135 (2) 150 (3) 208 (4) 663 (13) House finch 46 (2) 11(0) 17 (0) 2 (0) 7 (0) 83 (2) Red-winged blackbird 6 (0) 0 (0) 1 (0) 2(l) 3 (0) 12(l) Black phoebe 2 (0) 0 (0) 0 (0) 0 (0) 0 (0) 2 (0) California thrasher 2 (0) 0 (0) 0 (0) 2(l) 0 (0) 4(l) Spotted towhee 4 (0) 1 (0) 0 (0) 1 (0) 1 (0) 7 (0) Western scrub-jay 16(l) 1(0) 0 (0) 0 (0) 0 (0) 17(l) Sharp-shinned hawk 0 (0) 0 (0) 1 (0) 0 (0) 0 (0) 1 (0) Total 226 (7) 130 (0) 201 (2) 487 (6) 576 (4) 1,620 (19) Percent Non-target Loss (% Mortality) 1.17% When examining the non-target captures by month, no pattern emerges other than a gradual decline of California towhees after April (Figure 5). Non-target species diversity is lowest in June and highest in March. We eliminated data from Figure 5 that we collected in August since there was only one year of data (1998), and capture numbers were extremely low. Fifth Annual Report - 2002 7 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 November 2002 I Figure 4 Number of Non-target Species Captured Macano Canyon, Carlsbad, San Diego County • S. 5; -I. 4 - Figure 5: Non-target Species Captured by Month Macario Canyon, Carlsbad, San Diego County - -,. I •- -.; •;.,;4 4 4 -- ft Filth Annual Report-2002 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 1Aft - . - S4 - Non-avian species I Non-avian predators observed in our Macario traps included the long-tailed weasel, Argentine ant (Linepithema humile), southern pacific rattlesnake (Crotalus viridis), deer mice (Peromyscus I spp.), and black rat (Rattus rattus). It is highly probable that unobserved predators entered and escaped from traps. Other potential cowbird trap predators that occur in Macario Canyon include U feral cat (Fe/is catus), woodrats (Neotoma spp.), California ground squirrel (Spermophilus beecheyi nudipes), gopher snake (Pituophis catenifer annectens), and California kingsnake I (Lampropeltis getula californiae). With the exception of the feral cat, each of these species has been observed inside cowbird traps at other sites (W. Haas field notes), and all have been I observed within Macario Canyon but not inside our cowbird traps. During all years, we suspected long-tailed weasels to be harassing cowbirds at several I Macario traps. We found a weasel den and family in the vicinity of Trap 3 in 1999 (W. Haas field notes) and again noted an adult weasel in the vicinity of Trap 3 in 2001. We also frequently found I fecal pellets from murid rodents in and around seed pans in all Macario traps. We trapped house mice (Mus musculus) and several species of Peromyscus including deer mice (P. maniculatus) and I cactus mice (P. eremicus) from Macario traps. Ground squirrels (Spermophilus beecheyi) also furrowed under several of the traps and are another probable predator on trapped BHCO. I Ground squirrels are notorious predators and are capable of grabbing BHCO by the feet and pulling them through the mesh at the bottom of the trap (W. Haas field notes). I DISCUSSION I Potential Problems I Two problems typically affect cowbird tapping programs, vandalism and depredation. Both problems are expected while trapping cowbirds. We address both problems individually and suggest solutions or minimization strategies for each problem. Depredation Varanus biologists regularly observed avian and other predators within Macario Canyon during weekly least Bell's vireo surveys and while conducting daily cowbird trap checks. The Argentine ant and Cooper's hawk were most commonly encountered. The Argentine ant is an Fifth Annual Report -2002 9 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 November 2002 1 exotic invasive pest species. Argentine ants were omnipresent at the site, however we found very few exanimate cowbirds, the death of which could be attributed directly to this noxious pest. We frequently, however, observed Cooper's hawks in the vicinity of our cowbird traps, and on several occasions we observed Cooper's hawks capture and remove cowbirds from them. The Cooper's hawk, a year-round resident in coastal San Diego County, typically breeds in willow and oak riparian habitats as well as in eucalyptus groves. Adult Cooper's hawks are capable of removing birds from within cowbird traps by pulling them through the wire mesh. These voracious raptors are problematic, not only because they are known and capable predators able to take cowbirds from traps, but also because the Cooper's hawk is a state Species of Special Concern. Thus it is not an option to enact their relocation, especially since our data also suggest that the timeframe in which the greatest numbers of cowbirds are removed from our traps by Cooper's hawks correlates to the presence of nearby active Cooper's hawk nests. It is difficult to avoid impacts from this highly aggressive predator, often seen atop or near a cowbirds trap even upon close approach by the trap attendant. In 2001 we adopted a new trap design (Cornelius et cii 2000, Appendix C) for other trapping programs in San Diego County, which has helped reduce the incidence of raptor-caused depredation at these sites. Ground squirrels are also a potential problem because they dig under traps and may crawl through the slat board opening to obtain seed, and are well known for their omnivorous diet that includes not only seeds and flowers, but also birds and small mammals. Starting in 1999, to dissuade rodents, including ground squirrels, from entering cowbirds traps to steal seed and possibly injure or kill trapped birds, we placed seed in pans with 4-inch sides to avail the food source to captive cowbirds while minimizing spillage. This reduced availability of seed at the relatively unprotected bottom of the trap. The trap floor is typically constructed of the same mesh used for its sides and top. Minimizing spillage apparently reduces the interest level of scavenging rodents by minimizing the availability of a relatively easily accessible food resource. Ground squirrels are persistent scavengers of scattered seed and may otherwise have to be trapped out or euthanized when they have adverse impacts to target and non-target species. We attempted to discourage Argentine ants by avoiding direct contact of the traps with tree branches or trunks. While reducing the level of access, it is virtually impossible to avoid Fifth Annual Report -2002 10 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 November 2002 I: impacts to wildlife from Argentine ants in southern California riparian systems, especially when I providing a ready source of water as we do in our cowbird traps, necessary for sustaining trapped target and non-target bird species. Argentine ants presented a minor problem in Macario Canyon, causing the death of four to six cowbirds of the five-year trapping period. Vandalism Vandalism is often a significant problem during cowbird trapping. Impacts may include destruction of traps and/or releasing trapped target and bait birds. We placed traps in areas of relatively high security and low accessibility to the general public. We avoided areas with high public visibility, evidence of foot traffic, or proximity of heavily traveled roads. By discreetly placing our traps we hoped to reduce the potential costly impacts vandals may cause to cowbirds traps. We documented no incidents of vandalism to cowbird traps in Macario Canyon between 1998 and 2002. Signage in both English and Spanish may additionally reduce loss or damage to traps and birds. The information we posted visibly on each trap describing the purpose of and authority by which trapping -activity was carried out may have further reduced vandalism by explaining the need and legal authority by which trapping is carried out. These signs remained intact throughout the trapping period. RECOMMENDATIONS I Bait Birds • To effectively trap cowbirds, we strongly recommend that prior to inception of a trapping I program an adequate supply of bait birds be accumulated. Adequately supplying bait birds at trapping onset results in more rapid onset of target capture. The Macario traps minimally I • supported five BHCO each year from the onset of trapping. Our bait bird trapping is typically conducted at a dairy or ranch where cowbirds congregate in fall and winter. We have noted that the greater the number of bait birds placed in a trap (beyond the minimally prescribed total of five), the more enticing the trap becomes to other cowbirds. As population density within the trap increases, trap size becomes the limiting factor. As the season progresses, by early June, the' highly gregarious character of this species wanes, and trap success declines. . . Fifth Annual Report -2002 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. I 1 November 2002 Seed Pans We also recommend the practice of placing seed for trapped birds in a tray or other receptacle making for more sanitary trap conditions and reducing the impetus for ground squirrels and other rodents (for example, deer mice and exotic rats (especially, Rattus spp.) to enter traps. This practice also helps reduce seed germination (weed growth) in the vicinity of traps. We have observed at other cowbird trapping programs where seed that has been stockpiled at the bottom of a trap that, over time and weather conditions permitting, the seed can become contaminated with molds and fungi. We use high-sided galvanized aluminum, zinc, or plastic pans (4" high X 14" diameter) in all of our traps. These seed pans are much easier to maintain. In 2002 we instituted a new practice of adding a simple platform that separates the seed pan from the trap floor, further reducing the potential for rodents to access the food that sustains captive birds in our traps. The platform is simply made by attaching four 12" X 1" X 1" legs to a 12" X 12" piece of plywood. We placed one seed pan atop the platform, and a guzzler directly underneath. This system provides an additional benefit by minimizing the amount of algal growth by affording shade all day to the guzzler, thus reducing guzzler maintenance. When rainfall is imminent, the positions of the seed pans and guzzlers can be reversed, affording the seed a measure of protection rather than allowing it to become quickly saturated and virtually useless to entrapped birds. Trap Design We recommend that a Modified Mega-trap (Appendix C) such as that developed by John Cornelius (Hayden et at 2000)) or other suitable trap be adopted as the new cowbird trap standard. Since we began replacing modified Australian crow traps with modified Mega-traps traps at other cowbird trapping sites, we have significantly reduced in-trap cowbird mortality. At six San Diego County locations where we placed modified cowbird traps in 2002, we recorded no incidents of in-trap cowbird mortality. At two of the six modified Mega-trap locations (at Mission Trails Regional Park and in the San Pasqual Valley) we regularly observed adult female Cooper's hawks in the vicinity of or perched atop our traps, yet recorded no incidents of predator-caused mortality. At two of five standard (Australian crow) traps in Macario Canyon we recorded numerous instances of predator-caused mortality, primarily by adult Cooper's Fifth Annual Report - 2002 12 5-year Brown-headed Cowbird Trapping Program Varanus Biological Servicss, Inc. 1 November 2002 hawks, despite changing trap locations throughout the trapping period. DISCUSSION Our previous data document a notable decrease in the number of cowbirds observed and trapped in Macario Canyon between 1998 and 1999 (Varanus Biological Service 1998a, 1999). In 2000, the number of cowbirds trapped rose dramatically (Varanus Biological Services 2000) and in 2001 captures declined slightly, declining even further in 2002. During surveys and nest monitoring of the least Bell's vireo in Macario Canyon between 1998 and 2002, we recorded no incidents of brown-headed cowbird parasitism. We neither found cowbird eggs in LBVI nests nor vireos feeding juvenile cowbirds. Many of the trapped juvenile cowbirds were relatively old at the time of capture suggesting that they may have been derived from a remote location, and migrated subsequently to the Macario area. Irrespective of the origin of the juvenile cowbird population, our data indicate that, at minimum, cowbird numbers may vary from year to year in any area, and that trapping through the middle of July is justified. Because of the small number of LBVI nest attempts in Macario Canyon it is impossible to determine the impact of cowbird trapping on the Macario Canyon least Bell's vireo population. There are no historic nest monitoring data from the area thus there is no scientific basis for comparison. Recent records document low levels of vireo breeding success in Macario Canyon but fail to document the reasons for such. It is known that extremely low breeding success may occur in the absence of effective cowbird trapping programs, however vireo breeding success in Macario Canyon does not appear to be related to cowbird parasitism. Least Bell's Vireo Nest Success We recorded no incidents of nest parasitism on least Bell's vireo in 2002, nor in any of the previous four years of our concurrent cowbird trapping and least Bell's vireo surveys and monitoring. In 2002 we found a total of two nests constructed by one pair of vireos. The first vireo nest was abandoned prior to egg deposition. The reason for abandonment is unknown. The second nest produced two fledged young. Unlike the previous history of vireo pairs in the vicinity of Traps 1 and 2 (Varanus Biological Services 1998b, 1999) each nest was well constructed and sturdily suspended in native vegetation. Both nests were located in the North Mitigation site Fifth Annual Report - 2002 13 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 November 2002 where the vegetation has rapidly grown tall and dense over a three-year period. The vegetative structure in consort with the placement of two BHCO traps has possibly contributed to the successful fledging of young in Macario Canyon in 2002. :1 [I Fifth Annual Report - 2002 14 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 November 2002 LITERATURE CITED Braden, G. T., R. L. McKernan, and S. M. Powell. 1997. Effects of nest parasitism by Brown- headed Cowbird on nesting success of the California Gnatcatcher. The Condor 99:858- 865. Cornelius, J., G. Eckrich, and M. Goering. 2000. Hybrid Trap Design. U.S. Army, III Corps, and The Nature Conservancy of Texas, October 23, 2000. 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. Friedmann, H., L. Kiff, and S. Rothstein. 1977. A further contribution to knowledge of the host relations of the parasitic cowbirds. Smithson. Contrib. Zool. 235:1-75. Griffith Wildlife Biology (GWB) 1994. Cowbird trapping protocol. Unpublished document prepared by Jane C. Griffith and John T. Griffith, Griffith Wildlife Biology, Calumet, Michigan. I Hayden, T.J., D.J. Tazik, R.H. Melton, and J.D. Cornelius. 2000. "Cowbird Control Program on Fort Hood, Texas: Lessons for Mitigation of Cowbird Parasitism on a Landscape Scale," in J. Smith, T. Cook, S. Rothstein, S. Robinson, and, S. Sealy, eds., The Ecology and I Management of Cowbirds and Their Hosts (The University of Texas Press, Austin, TX). I Ortega, C. 1998. Cowbirds and other brood parasites. University of Arizona Press, Tucson, Arizona, USA. I Robinson, S. K., J. A. Grzybowski, S. I. Rothstein, M. C. Brittingham, L. J. Petit, and F. R. Thompson 1993. Management implications of cowbird parasitism on neotropical migrant songbirds. Pages 93-102 in D. M. Finch and P. W. Stangel (ed.). Status and I . management of neotropical migratory birds. USDA Forest Service General Technical Report RM-229. Rosenberg, K.V. and R. Bonney. 1994. The National Science Experiments: Birds Like Millet And Milo Too! Birdscope, Volume 8, Number 4. I 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- I 16482. U.S. Fish and Wildlife Service. 1998. Draft Recovery Plan for the Least Bell's Vireo (Vireo be/lu pusullus). Portland, Oregon. 139 pp. Fifth Annual Report -2002 15 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 November 2002 I I Unitt, P. 1984. The birds of San Diego County. Memoir 13. San Diego Society of Natural History. I Varanus Biological Services, Inc. 1998a. First annual report 5-year Brown-headed Cowbird Trapping Program. Cannon Road Extension Wetlands Mitigation Project Macario I Canyon, Carlsbad, San Diego County, California City Project No. 3184. Varanus Biological Services, Inc. 1998b. First annual report least Bell's vireo trapping program; I Cannon Road Extension Wetlands Mitigation Project Macario Canyon, Carlsbad, San Diego County, California City Project No. 3184. I Varanus 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 City Project No. 3184. Varanus Biological Services, Inc. 2000. Third annual report 5-year Brown-headed Cowbird Trapping Program. Cannon Road Extension Wetlands Mitigation Project Macario Canyon, Carlsbad, San Diego County, California City Project No. 3184. Weidensaul, S. 1991. The Birder's Miscellany. New York: Simon & Schuster: 50 Fifth Annual Report -2002 16 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 November 2002 Appendix A Letters of Authorization CDFG USFWS Fifth Annual Report - 2002 17 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 November 2002 I State of California - The Resources Agency DEPARTMENT OF ASH AND GAME http://www.dfg.ca.gov 1416 Ninth Street Sacramento, CA 95814 (916) 653-4875 March 18, 2002 Mr. William E. Haas Varanus Biological Services, Inc. 7920 Silverton Avenue, Suite D San Diego, California 92126 Dear Mr. Haas: This is in response to your letter to the Department of Fish and Game requesting perm i s s i o n t o capture the brown-headed cowbird (Molóthrus.ater) in 2002 using modified Australian crow traps and similar traps. Although the letter does not cite thepurpose of the proposed work, it is like l y t h a t V a r a n u s Biological Services intends to reduce nest parasitism by The cowbird on the southwes t e r n w i l l o w flycatcher (Empidonax traillii extimus), least Bell's 'virëô (Vireo bellii pusillus), California gnatcatcher (Polioptila calfornica), or similar species. I This letter authorizes you and other employees aiidfassotes of your firm to conduct co w b i r d trapping in 2002, if Varanus Biological Services agrees to dojllowing I Release no captured cowbirds other than males v sI1arked with federal metal leg-bands, except as approved by Dr. John Gustafson, nent's representative for cowbird-trapping I 2 Report the federal band number of eacarwbird, either male or female, that is cap t u r e d to the U S Bird Banding Laboratory (l/according to the instructions at the BBL ' s w e b s i t e (http://www.pwrc.usgs' gov/bbl/) I Obtain permission of the landowner or operator before enteringa j ope . , either public or private, to place a trap. . Label each trap with your firm's name and telephone number of contactperson. I s. Place each trap in such a man er iliat4fig'Aaided in:the:hotter part.of the day or provide shade. 6. Check each trap no less often than once every 24 hours, to release non-target birds an d m a i n t a i n .water, birdseed, and perches in the trap. I 7. Consider releasing no captured European starling (Sturnus vulgaris) and house sparrow (Passer domesticus). I 8. Mark no birds taken from traps, unless the person marking has a federal permit for markin g o r i s named on another person's federal permit for marking and the permit allows marking o f t h e ' particular species. 9. Mark no captured cowbirds, except as approved by Dr. Gustafson. I - I. 1, I I I I Mr. William E. Haas March 18, 2002 Page Two I 10. Dismantle all traps at the end of your work. 11. Submit a report to Dr. Gustafson by October 31, 2002 which provides details of your 2002 work and results, as follows: location of each trap (county, township, range, and quarter section); I numbers of the cowbird, starling, and house sparrow captured and not released at each site by date; and species and numbers of captured birds released alive and found dead at each site by date. I 12. Provide to Dr. Gustafson the name of each employee or associate of Varanus Biological Services, other than yourself, within 30 days of assignment of the person to cowbird trapping. I Please indicate your agreement to the terms of this authorization by signing and dating this letter and its enclosed copy in the provided spaces below. Retain one letter and mail the other to Dr. Gustafson I in the Habitat Conservation Planning Branch at the letterhead address. Each employee or associate of your company who is assigned to cowbird trapping must possess a copy of the fully-signed letter whenever that person is operating cowbird traps. I Varanus Biological Services may be required to obtain approval for cowbird trapping from the U.S. Fish and Wildlife Service. We recommend that you contact Ms. Christine Moen at (760) 431-9440 or at Christine_Moenfws.gov for further information. Please address all matters regarding this letter to Dr. Gustafson. The authorization for 2002 is subject to renewal for 2003 and subsequent years with Dr. Gustafson's written approval. For work in 2003, Varanus Biological Services may request renewal after December 1, 2002 by sending a letter to him. If you have questions about this letter, please contact Dr. Gustafson by e-mail at JGustafsdfg.ca.gov or by telephone at (916) 654-4260. Dale T. Steele, Supervising Biologist Habitat Conservation Planning Branch C~ - acall-1 1~ ~- - William E. Haas' Date: Enclosure cc: See page three. United States Department of the Interior Fish and Wildlife Service Ecological Services Carlsbad Fish and Wildlife Office 2730 Loker Avenue West Carlsbad, California 92008 William Haas Varanus Biological Services, Inc. 7920 Silverton Avenue, Suite D San Diego, California 92126 Re: Brown-headed cowbird trapping Dear Mr. Haas: - MAR 18 2002- We have reviewed the request and proposal to conduct trapping and removal of brown-headed cowbirds (Molothrus ater: cowbirds) in areas that support bird species listed under the federal Endangered Species Act of 1973, as amended (Act). This request was submitted by Kylie Fischer, of your company, on your behalf. We support and encourage cowbird trapping activities because cowbirds are not native to southern California and their presence has resulted in the decline and/or reduced productivity of several listed bird species (e.g., least Bell's vireo [Vireo be/li pusillus], southwestern willow flycatcher [Empidonax traillii extimus], and coastal California gnatcatcher [Polioptila calfornica cahfornica], among others.) Guidance for conducting cowbird trapping is described in the 1994 unpublished document written by Griffith Wildlife Biology titled "Brown -headed cowbird trapping protocol" and is available from our office upon request. We will consider alternative methods, but a proposal must be submitted in writing and authorized, in writing, by a letter from our office. Cowbird management programs, when properly conducted, are consistent with the recovery goals for listed bird species because they enhance the reproductive potentials of the listed birds by reducing cowbird nest parasitism. In the interest of effective parasitism reduction of sensitive bird species and the minimization of risks to non-target species, we emphasize the importance of optimal timing and duration of the trapping effort. Regarding the humane treatment of trapped birds, it is important that each trap is checked and maintained at least once every 24 hours and that all non-target birds are released from traps immediately upon their discovery. Please refer to an approved protocol for guidance in these matters. In addition, any and all traps shall be moved whenever necessary to maximize the efficiency of the trapping effort or to reduce real or potential impacts to non-target species. In an attempt to understand the life history, status, and distribution of cowbirds, we are authorizing and facilitating studies of cowbirds that utilize color-banding and tracking of individual birds. Therefore, observations of all marked or banded cowbirds should be recorded and reported to the U.S. Geological Survey Bird Banding Lab (http://www.pwrc.usgs.gov/bbll, or 1-800-327-BAND) as soon as possible. Once necessary data (e.g., band number, location and I William Haas 2 sequence of color bands or other markers) is noted, marked or banded male cowbirds should be released at the point of capture. All marked or banded females and unbanded cowbirds should be euthanized at the point of capture unless alternative measures have been previously authorized by our office. The accidental capture, harm, or death of non-target bird species shall not exceed two percent of total captures (of non-target species.) If this amount is exceeded you are instructed to cease trapping and consult with the Staff Ornithologist or Recovery Permit Coordinator of our office to discuss methods to reduce the incidental mortality of your activities. This guidance to conduct cowbird trapping activities requires that you submit reports by the last day of each calendar year to our office (see letterhead address, attn: Recovery Permit Coordinator) and expires two years from the date of this letter. The reports shall include, but not be limited to, the folio Xing . . .................. . ....... Copies (8.5 x 11 inches) of USGS 7.5" maps depicting the location of traps, including the quadrangle name and County. The number of active days the trap was deployed. The number and sex of cowbirds captured in each trap. The number of banded cowbirds including USFWS band number, date, and location of capture. I • The number and species of non-target birds incidentally captured, harmed, or killed and the location of each capture. We appreciate your efforts toward the recovery of listed bird species that are negatively impacted by cowbirds. Please note that you will also need a letter of authorization from the California Department of Fish and Game for this activity. Please contact John Gustafson (CDFG) at (916) I 654-4260 or at JGustafsdfg.ca.gov. Please direct correspondence regarding this authorization to the Permit Coordinator of this office at the letterhead address or at (760) 431-9440. Sincerely, Andrew R. Yuen Deputy Field Supervisor cc: John Gustafson (Calif. Dept. Fish and Game) 1-6-02-RP- 163 (BHCO-0 10) Appendix B Daily capture records - BHCO Daily capture records - Non-target species I U Fifth Annual Report - 2002 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 November 2002 22 New Capture Dates for 2002 at Macario Canyon BHCO Traps Month Date Male BHCO Female BHCO Juvenile BHCO March 16-Mar-02 1 0 0 17-Mar-02 2 0 0 18-Mar-02 1 0 0 23-Mar-02 1 0 0 28-Mar-02 1 1 0 29-Mar-02 1 0 0 April 06-Apr-02 0 1 0 08-Apr-02 0 1 0 09-Apr-02 1 0 0 12-Apr-02 1 0 0 17-Apr-02 1 2 0 30-Apr-02 3 0 0 May 01-May-02 1 1 0 06-May-02 2 0 0 07-May-02 1 0 0 16-May-02 1 0 0 17-May-02 2 1 0 June 11-Jun-02 1 0 0 15-Jun-02 2 0 0 20-Jun-02 0 0 1 July 05-Jul-02 0 0 1 Total 2002 23 7 2 Fifth Annual Report - 2002 23 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 November 2002 Non-target Capture Dates for 2002 at Macario Canyon BHCO Traps Month Date SOSP CALT HOFI RWBL SPTO Alive Dead Alive Dead Alive Dead Alive Dead Alive Dead March 17-Mar-02 1 0 0 0 0 0 0 0 0 0 18-Mar-02 3 0 0 0 0 0 0 0 0 0 19-Mar-02 2 0 0 0 0 0 0 0 0 0 20-Mar-02 1 0 1 0 0 0 0 0 0 0 21-Mar-02 3 0 2 0 0 0 0 0 0 0 22-Mar-02 3 0 6 0 0 0 0 0 0 0 23-Mar-02 5 0 4 0 0 0 0 0 0 0 25-Mar-02 1' 0 0 0 0 0 0 0 0 0 26-Mar-02 2 0 4 1 0 0 0 0 0 0 27-Mar-02 6 0 1 0 0 0 0 0 0 0 28-Mar-02 3 0 3 2 0 0 0 0 0 0 29-Mar-02 3 0 3 0 0 0 2 0 0 0 30-Mar-02 1 0 3 0 0 0 0 0 1 0 April 01 -Apr-02 2 0 3 0 0 0 0 0 0 0 02-Apr-02 2 0 2 0 0 0 0 0 0 0 03-Apr-02 4 0 2 0 0 0 0 0 0 0 04-Apr-02 4 0 3 0 0 0 0 0 0 0 05-Apr-02 2 0 2 0 0 0 0 0 0 0 06-Apr-02 1 0 3 0 0 0 0 0 0 0 08-Apr-02 1 0 1 1 0 0 0 0 0 0 09-Apr-02 2 0 1 0 0 0 0 0 0 0 10-Apr-02 3 0 1 0 0 0 0 0 0 0 11-Apr-02 4 0 1 0 0 0 0 0 0 0 12-Apr-02 2 0 1 0 0 0 0 0 0 0 13-Apr-02 6 0 0 0 0 0 0 0 0 0 15-Apr-02 8 0 0 0 0 0 0 0 0 0 16-Apr-02 5 0 0 0 0 0 0 0 0 0 17-Apr-02 5 0 0 0 0 0 0 0 0 0 19-Apr-02 4 0 0 0 0 0 0 0 0 0 20-Apr-02 3 0 0 0 0 0 0 0 0 0 22-Apr-02 4 0 0 0 0 0 0 0 0 0 23-Apr-02 6 0 1 0 0 0 0 0 0 0 25-Apr-02 1 0 0 0 0 0 0 0 0 0 26-Apr-02 0 0 1 0 0 0 0 0 0 0 27-Apr-02 5 0 0 0 0 0 0 0 0 0 29-Apr-02 4 0 1 0 0 0 0 0 0 0 30-Apr-02 5 0 1 0 0 0 0 0 0 0 Fifth Annual Report - 2002 24 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 November 2002 HOFI Alive Dead 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 RWBL Alive Dead 0 0 0 0 0 0 0 0 0 0 '0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ' 0 0 0 SPTO Alive Dead 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 1 0 0 0 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 '0 0 0 0 0 0 0 0 0 0 ' 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 25 Month Date SOSP CALT Alive Dead Alive Dead May 01-May-02 5 0 2 0 02-May-02 2 0 2 0 03-May-02 8 0 4 0 04-May-02 8 0 2 0 06-May-02 4 0 3 0 07-May-02 2 0 4 0 08-May-02 2 0 3 0 09-May-02 3 0 2 0 11-May-02 10 0 5 0 13-May-02 3 0 4 0 14-May-02 2 0 3 0 15-May-02 5 0 4 0 16-May-02 5 0 4 0 17-May-02 3 0 2 0 18-May-02 5 0 3 0 20-May-02 5 0 4 0 21-May-02 6 0 4 0 22-May-02 2 0 4 0 23-May-02 5 0 5 0 24-May-02 4 0 4 0 25-May-02 5 0 4 0 26-May-02 3 0 3 0 28-May-02 3 0 5 0 29-May-02 4 0 2 0 30-May-02 7 0 3 0 31-May-02 4 0 3 0 June 01-Jun-02 7 0 3 0 03-Jun-02 3 0 3 0 04-Jun-02 6 0 2 0 05-Jun-02 4 0 2 0 06-Jun-02 2 0 0 0 07-Jun-02 5 0 0 0 08-Jun-02 5 0 2 0 10-Jun-02 3 0 4 0 11-Jun-02 5 0 2 0 12-Jun-02 3 0 2 0 13-Jun-02 5 0 2 0 14-Jun-02 5 0 3 0 15-Jun-02 1 0 1 0 18-Jun-02 3 0 '2 0 20-Jun-02 5 0 2 0 21-Jun-02 2 0 2 0 Fifth Annual Report - 2002 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 November 2002 Month Date SOSP CALT HOFI RWBL SPTO Alive Dead Alive Dead Alive Dead Alive Dead Alive Dead 23-Jun-02 4 0 3 0 0 0 0 0 0 0 25-Jun-02 4 0 2 0 0 0 0 0 0 0 26-Jun-02 4 0 2 0 0 0 0 0 0 0 27-Jun-02 3 0 3 0 0 0 0 0 0 0 28-Jun-02 4 0 2 0 0 0 0 0 0 0 29-Jun-02 6 0 3 0 0 0 0 0 0 0 July 01-Jul-02 5 0 2 0 0 0 0 0 0 0 02-Jul-02 2 0 2 0 0 0 0 0 0 0 03-Jul-02 1 0 2 0 0 0 0 0 0 0 05-Jul-02 5 0 2 0 0 0 0 0 0 0 07-Jul-02 2 0 2 0 0 0 0 0 0 0 08-Jul-02 4 0 2 0 0 0 0 0 0 0 10-Jul-02 4 0 2 0 0 0 0 0 0 0 12-Jul-02 5 0 2 0 0 0 0 0 0 0 13-Jul-02 4 0 1 0 0 0 0 0 0 0 15-Jul-02 4 0 1 0 0 0 0 0 0 0 Total 2002 357 0 204 4 7 0 3 0 1 0 Fifth Annual Report - 2002 26 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 November 2002 I: I I - I Hybrid Trap Design I I I 1 II , I I . * I.. I I I Fiflh Annual Report - 2002 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1 November 2002 Appendix C 27 - - - - - - - - - - - - - - - - - - - 69 _____ - - ir Construction Tips- Portable Trap .1110 heeled lumber )to0Jg1oUt The 0111104 IntIet CCII Is contpcn10le0l by longer turd be and reduced ordotenorlcer - Zen l r lumber errS you are recite to dad wat6rg. Tipped lumber will ban and hotel Into an rmusedte moo S alared teethe several doy .11100 Wed broctet Pt dhgmat corners to uquore each pallet bolero 0110ch1rr9 guo101h This Of also edt an panel .10 cur guwetL lay cute theet at ptyeood In 12 Inch uqrrnre& lhern draw diagonals ocrasu the sWores. A Wheel of pirevod rell moIre 64 gussets. .Guocls go on core 040 Cl panel, tralecr000 attaches to the other ship. For side and top p000ll lute ott end up behrg an the horde Cl the panel. This; preuorrts bIrds from roaslbrg on trorneool next to v6e vAere they are prone to predation.*Exception: End panels ore constructed the acyro eroy, but doIng assembly, the ute goes at the cutede6 becoree the drop errllcorCe attaches to hodtonlGt menibels for structural otobbly. .this pattern Is designed to we 480th ohio hcrzscreon to maximum ettldoncy. Internal crow members ore placed toosorrhe dpirt oceltath Wide h05sct00nw8 probably not be readily available In dock, but arm buiheug supply can order IL Jo rnerdmtze strep efficbrm, use this ploceco Cut gussetri ep lumber, precut lengths, cur cut dot oowiibty, assemble 611th top, and end pallet llamas attach h0bcroo4 fIner assembly Whoa but-dog rnrj)pie urdlt pertwrnhrg drnsar others ta o000rot traps at the acne £ne Will allow you to develop an assenibty lIre process Oral cuts cornhuclar time per urdL mur %--Td1h of 125 trr-lun.b. dell assembly kn critical dimension. Wider slob wIl Increase non- 41 iru-.1. P 1— - MI 00 1 T I, -rLa ,4 Back Panel Materials List for 6 x 8 Portable Cowbird Trap Number 16 Desarlotton Comments It-p 2x4 hito 202 2u4o8 (healed) 2 Sheets t12 Inch CDX plhwaod (healed) 1 drool Is (Cr stat ossemblel and I sheet t to ax) up for guwett. - 64 Smear reel t12 Inch MOM h0ka00rr sought In )pp tool ids I pab ltgtrt pin IrInges (3 Inch) Door hinges Semen door handle Outdde at 60Cr Gctrradzod rIGID 14 112 boIl) We With padrock tot recrully - Screen dccl latch 111011 on bode of door 14 10 12 Inch shell blactote Used to square panels 12 pm panel) 125 (oppca) (Inch dIrect scram herd assembly at slot assembly, ctlrsddrrg shell brackets to panels 50 )0ppr64 3 Inch gatuonlzed deck screws FIeld assembly (panel to panel) 300 (approxl 6001— 1112 Itch pneumatic staples I 0,.-0, ,ucrrr,retlu danIel 1110410 COach gussets Used 10 attach screen to panels et cgoturrext ineurtling Vasirels and Shcrrpotftied holft Witch will daughter Your clecoyst.. Escapes by lerrreth cowbIrds also Increase wIth udder dole .We parsebattachrta the ootddeof end P000le Nothing ends OUIdde. -. Top Panel/Slot Assembly Right Side Panel. Left Side Panel (me as right - ru -_l osr[ 1P -_ -. Finished HYBRID Trap -1 -Jv Recommended Tools for [ End Mew of lop neVS(ot Assembly Construction Shop ossemblyor panels (able row- for ripping 24 Ct-rap row. he cutting boards to lorrgth bechrc hand row. for oilIng cut gunseb and stat Front Panel assembly Itetrocledle rule -Ia meaoulrrg dhrronttoflt IlecIrlu of cadiets drtf/dlteos-let dilstng spew, F—'- —I Door pnerzrrrafc or electric: rthbter' for aatltrrg proJ SCIEWn thresurratla stapler' (a attaching gussets and wire hlesmrorrclrate,. far asserhrb+fatparr$Is(optihoatbut helpftd par-red can be assembled rsl)h 3 Inch deck ccrorllt-rroielb net available) T FIetd assembly Cadoss dzWddvw' tot 4IhIrrg spent am at soap - to kibricale, =avi threads - - HYBRID TRAP DESIGN U.S. Army. ))( CORPS, and The Nature Conservancy of Texas John D. CornelIus, G)( EcktlCh and Mark D. Goering ______ October 23, 2000 SCALE: 1' = V . 1 '4 4! • -Lt.&- '-,.z I ?'• fi - .. •.1 .-':' •2;'•-rt4'-•.- .-:.I •'-''- . _'1• ' ?-_-', .A ' -•, - - - -'.. . . - ''. -:- ' • • • J. •• . -'.-•...' -- ..•• . • .•--• • • • •'- . - • • - I Introduction The City of Carlsbad is required to implement a brown-headed cowbird (Molothrus ater, BHCO) trapping program in Macario Canyon. This program is part of the biological mitigation 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, Biological Opinion No. 1-6-97-F- 51). The focus trapping area for the program is the north end of Macado Canyon, Carlsbad, San Diego County, California. The canyon is characterized by hillsides of native Coastal Sage Scrub and agricultural fields. Runoff from upstream development and the adjacent agricultural fields is sufficient to support Southern Willow Scrub and Southern Cottonwood-willow Riparian Forest habitat along the bottom of the canyon. Drainage from the canyon feeds into Agua Hedionda Lagoon at its northern end. The cowbird trapping program is specifically designed to support recovery of the federally listed endangered least Bell's vireo (Vireo bellii pusillus, LBVI). Least Bell's vireos are small, insectivorous migratory songbirds of extremely limited range. Wintering in Baja California, Mexico, LBVI migrate northward to their breeding grounds in southern California between mid- March and early April. They typically nest in early successional willow-riparian habitats characterized by the presence of dense understory vegetation. Once widespread in low-elevation riverine valleys as far north as Tehama County in northern California, least Bell's vireo population numbers declined dramatically between the 1940's and mid-1980's. Two factors are primarily responsible for this species' demise and hence have contributed to its status as an endangered species: habitat loss resulting from eradication, fragmentation and degradation of southern California riparian corridors, and brood parasitism by BHCO. The explosive increase in BHCO population outside its historic range has accompanied the decline of riparian habitat. In southern California, the increase in BHCO has also paralleled the. decline in numerous other songbird populations including yellow warbler (Dendroica petechia) and warbling vireo ( Vireo gilvus) in San Diego County (Unitt 1984). Fourth Annual Report -2001 1 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. November 2001 Brown-headed cowbirds were historically associated with buffalo and possibly antelope herds, and subsequently livestock in the Great Plains of the United States. It is hypothesized that brood parasitism in BHCO evolved to accommodate the species' reliance on benefits gained foraging among herds of nomadic hoofed mammals. When, for instance, nomadic herds of buffalo moved, cowbirds followed suit. Female cowbirds depositing eggs in other species' nest would potentially achieve the equivalent of "nest success" at the expense of parasitized hosts while allowing the cowbirds to follow the buffalo herds. Brown-headed cowbirds have been documented using at least 130 bird species as hosts (Friedmann et al. 1977). Brood parasitism of least Bell's vireo by BHCO has been well documented. The history of brown-headed cowbird-least Bell's vireo interaction is summarized in Franzreb (1989). Trapping of BHCO using modified Australian Crow Traps is an accepted method of reducing brood parasitism in least Bell's vireo (Ibid.) as well as other riparian and non- riparian species (for example, southwestern willow flycatcher (Empidonax traillii extimus), Whitfield and Strong 1995). Only since the onset of cowbird trapping and riparian habitat preservation and restoration have least Bell's vireo populations begun to rebound. Between the early 1980's and 1990, cowbird parasitism of least Bell's vireo at Marine Corps Base, Camp Pendleton fell from 47 percent to less than 1 percent. Between 1986 and 1996, the Santa Margarita River vireo population on Camp Pendleton rose from 68 pairs (98 territorial males) to 456 pairs (523 territorial males) (Fish and Wildlife Service 1998). Trapping programs along the Sweetwater River, San Diego River, and the San Luis Rey River in the vicinity of Oceanside have resulted in "similarly dramatic reductions in the rate of nest parasitism coincidental with implementation of cowbird control programs" (Ibid. p.34). Methods In 2001, Varanus Biological Services, Inc. (Varanus), under contract to Native Landscape, Inc., was responsible for implementing the fourth year of the City's cowbird trapping program in Macario Canyon. Cowbird trapping was performed under authorization issued to Varanus from both the USFWS and California Department of Fish & Game (CDFG). The contract specified a Fourth Annual Report -2001 2 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. November 2001 •.• . •..... Nt total of five traps (Figure 1). Figure 1: 2001 Brown-headed Cowbird Trap Locations • Macario Canyon, Carlsbad, California 471000mE. WGS64 Zone 115 4 72000mE. . v '-• E .4 0 0 C) z E • - 0 0 - 0 0 Cl) E o o 0 w • • E -. o 0 0 - - r • 471000mE. WGS84 Zone 115 472000mE. - - . . 0 1/2 iMLE TNTJIVIN --.---- - -=- - - I, -- 0 1000FEET 0 500m 1000 - • I I-I I-I I-I I-I I-.I I-t I-I I • j 130 Printed fit)m TOPO! @2000 Wildflower Productions (www.topo.com) 5-, In order to efficiently attract free-flying BHCO into cowbird traps it is usually best to provide each trap with an initial group of "bait birds" Song and activity of the bait birds are attractants to free-flying BHCO. Dairies, feedlots, livestock pastures and horse stables are all excellent sources (•. from which to obtain bait cowbirds if trapping is done prior to cowbird dispersal into breeding • habitat. Prior to initiating the trapping program, we set up two cOwbird traps at the Hollandia Dairy, San Marcos, San Diego County. Because of the density of BHCO al the dairy, we only.' • ,needed to supply the traps with an abundance of seed and water and beganto trap cowbirds • Fourth Annual Report -2001 . - rr 5-year Brown-headed Cowbird Trapping Program - - I' • - Varanus Biological Services, Inc. • - .. . - • •.. .. . , November2001 - . - • . t i• •. • •:. within 24 hours of trap set-up. The two dairy traps provided enough bait birds for all of the Macario Canyon traps (n=25). Because of potential bait bird loss from traps in Macario Canyon, Varanus maintained the feeder trap at the Hollandia Dairy through 30 April and also maintained a small colony of cowbirds at a secure location through the end of the trapping season. Operating a trap at the dairy and subsequent sequestering of a small quantity of BHCO ensured availability of an adequate number of bait birds ( a minimum of five birds/trap) throughout the trapping period in the event of vandalism or other events that might have reduced the number of BHCO in our traps. We deployed a total of five traps in Macario Canyon on 15 March. Confining our trapping program to the area most heavily frequented by LBVI since 1995; we placed four of the traps at regularly spaced intervals along the eastern edge of the riparian vegetation within the canyon. We placed a fifth trap along the western edge where we also documented frequent LBVI activity since 1998. Activation of BHCO traps required baiting them with a minimum of five male brown-headed cowbirds and supplying each trap daily with fresh water and seed. We wing-clipped (shortening the primary or flight feathers of the right wing) all bait birds to ensure that, in case of release due to vandalism or accidental escape, flight capability was severely impaired and potential breeding success greatly limited. Wing-clipped birds are typically easy prey for raptorial species, including locally common Cooper's hawks (Accipiter cooperi) and short-tailed weasels (Mustelafrenata). We posted a laminated sign on each trap describing the purpose and techniques of cowbird trapping. The description was posted in English and Spanish. Following activation, traps were checked daily to wing clip or remove and euthanize any new (that is, newly trapped) cowbirds and to release captured non-target species. During each visit, seed pans and water dispensers were cleaned and fresh seed and water added. To limit the attractiveness of traps to certain non-target species, especially seed-eating passerines such as house finches (Carpodacus mexicana), from entering the cowbird traps we chose a seed mix composed primarily of white millet that did not include sunflower seeds. The cowbird trapping regime lasted a period of 124 calendar days. All traps were deactivated, dismantled, and removed from the canyon on 17 July. All remaining bait Fourth Annual Report -2001 4 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. November 2001 and captured BHCO were euthanized at that time. Results We captured a total of 76 BHCO as a result of this focused cowbird trapping effort (Table 1); 45 were adult males, 17 were adult females, and 14 were juveniles (young of the year). It was not possible to determine the origin (location) of juvenile cowbirds captured in Macario Canyon. Captures of adult male BHCO occurred in each month of trapping but declined from a maximum of 16 in March (in only '/2-month of trapping) to two captures in June and July. Most juvenile BHCO captures occurred in June with the earliest capture on 26 May. The number of total captures declined each month from March to May. Total captures in May and June was similar. In terms of total numbers captured, a decrease in the number of adults captured between May and June was offset by the increase in number of juveniles entering the trap. Capture rate declined precipitously from June to July (Figure 2). We recorded no incidents of vandalism during 2001. Eighteen individuals suffered in-trap depredation. A net total of six individuals escaped while an attendant opened a trap door or by using "other means of egress". When we suspected BHCO had escaped by other means of egress we inspected each trap closely to determine the means of escape. If a flaw in a trap was discovered (for example, wire mesh that had been displaced from handling) we repaired the flaw immediately. During 2001 we detected no flaws in our traps. We do not have any indication of how several of the BHCO escaped. It is possible that harassment by accipiters or other possible predators may have resulted in the escape, however improbable, via the same opening used for entering the traps. We have documented that Cooper's hawks (Accipiter cooperii) and sharp- shinned hawks (Accipiter striatus) cause cowbird mortality within cowbird at Macario Canyon traps (Varanus Biological Services 2000). We have observed Cooper's hawks "working" the BHCO traps by scaring trapped cowbirds from the bottom of the traps into the apical corners of the trap, grabbing the cornered birds with talons and then decapitating them. Cooper's hawks may succeed in removing the head only, or may be able to pull the entire carcass through the wire mesh leaving telltale feathers attached to the wire grid. They may also extract fallen carcasses if Fourth Annual Report -2001 5 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. November 2001 Table 1. Brown-headed Cowbird Trapping Results: Macario Canyon, Carlsbad, California' (March - July 2001) : Category (Age and Sex) of Brown-headed Cowbird (BHCO) Captured Number (combined, all traps) BHCO, Captured - Adult Female :• .17 BHCO, Captured - Adult Male 45 BHCO, Captured - Juvenile ,. . 14, BHCO, banded males -. 4. () Total BHCO Captured 76 BHCO, depredated in trap (by Cooper's hawk, or other) .. . (18) Escaped -6 - Trapped BHCO Removed from Macario Canyon I 70 BHCO, bait birds from Hollandia Dairy 25, Total BHCO removed from population -• (includes 25 bait birds) . 95 .- Figure 2: Number of Brown-headed Cowbird Caught . . Per Month 15 March through 17 July, 2001 .. Macario Canyon, Carlsbad, San Diego County . - 18 . U 10- 4. Males Females 6- 0 Juveniles J March April May June July • • 7 .-.•.••• . Month ,. Fourth Annual Report -2001 - -. . . . • : 6 .• 5-year Brown-headed Cowbird Trapping Program . • -- . •• • Varanus Biological Services, Inc. - • • •• November 2001 . . I . .• the cowbird falls sufficiently close to the edge of the trap. As a result of trapping within Macario Canyon and the initial supply of 25 bait birds we removed a total of 95 BHCO from the local population (Table 1). Non-target Species We recorded a total of 486 non-target bird (that is, non-BHCO) captures in Macario Canyon cowbird traps in 2001 (Table 2, Figure 3). Song sparrow (Melospiza melodia) was the most frequently trapped non-target species, followed by California towhee (Pipilo crissalis). We also captured two California thrashers (Toxostoma redivivum), two house finches, two red-winged blackbirds (Agelaius phoeniceus), and one spotted towhee (Pipilo maculatus). Non-target mortalities included three California towhees, one red-winged blackbird, one song sparrow, and one California thrasher. Frequency of non-target captures was highest in the later part of the trapping season. This frequency pattern is typical for cowbird trapping programs. Table 2. Non-target Species Captured During Brown-headed Cowbird Trapping at Macario Canyon, Carlsbad, California, March - July, 2001 Non-target Species (Scientific Name) Total Number Trapped Total Deceased/ Depredated Deceased Song sparrow (Melospiza melodia) 331 1/0 California towhee (Pipilo crissalis) 150 3/0 House finch (Carpodacus mexicana) 2 0/0 California thrasher (Toxostoma redivivum) 2 1/0 Red-winged blackbird (Agelaiusphoeniceus) 2 1/0 Spotted towhee (Pipilo maculatus) 1 0/0 Total Non-target Captures 486 6 Percent Non-target Loss (% Mortality) 1.2 % Fourth Annual Report -2001 7 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. November 2001 • Figure 3: Number of Non-target Species Caught Per Month 15 March through 17 July, 2001 180 - 160 * 140 120 100 80 iiJ FJI7 60 [1 ° Z 20 * - March April May June July Month 3. Macano Canyon, Carlsbad, San Diego County Non-avian species '• -.. . . This year we found no non-avian species in our traps upon our arrival. Howeve, from the number - of BHCO found depredated, it is highly probable that unobserved predators entered and escaped • . from traps. Potentially occurring predators are long-tailed weasels (Mustela frenata), woodrats (Neotoma spp), deer mice (Peromyscus spp) and black rat (Rattus rattus) All have been observed inside cowbird traps (W Haas field notes) In 2001, we suspected long-tailed weasels to be harassing cowbirds at several Macano traps We found a weasel den and family in the vicinity of Trap 3 in 1999 (W Haas field notes) and again noted an adult weasel in the vicinity of Trap 3 in 2001 We frequently found fecal pellets from murid rodents were m and around seed pans in all Macario traps in 2001. It is probable that house mice (Mus musculus) and several species of Peromyscus including deer mice (P maniculatus) and cactus mice (P. eremicus) entered the traps in our absence. Ground squirrels (Spermophilus beecheyi) also furrowed under several of the traps and are another probable predator on trapped BHCO. Ground squirrels are notorious . predators and are capable of grabbing BHCO by the feet and pulling them through the mesh at the - bottom of the trap (W. Haas field notes). • . .* - - '. -.-. Fourth Annual Report 2001 8 5-year Brown-headed Cowbird Trapping Program - Varanus Biological Services Inc November 2001 - V. • • •I ••, - • •.'• Problems We anticipated two potential problems of cowbird trapping in Macario Canyon and we implemented strategies to minimize or eliminate them. Each perceived problem is addressed individually and our solutions or minimization strategies are suggested. Problem #1: Depredation A large number of potential cowbird predators inhabit Macario Canyon. Potential trap predators detected in or around the cowbird traps since this project's inception include Cooper's hawk, sharp-shinned hawk, long-tailed weasel, ground squirrel, coyote (Canis latrans), bobcat (Lynx rufus), feral cat (Felis catus), dusky-footed woodrat, black rat, southern pacific rattlesnake, and Argentine ant (Linepithema humile). To dissuade rodents from entering cages and possibly killing or injuring target or non-target birds, we placed birdseed in galvanized metal or plastic pans 4" high by X 14" diameter. Locating traps to avoid contact with willow branches helped deter Argentine ants. Unfortunately, this introduced species of ant is omnipresent in most riparian habitats in southern California and is difficult to exclude. They typically invade all cowbird traps to some degree, apparently to access water guzzlers. Keeping traps out of contact with surrounding vegetation appears to limit their occurrence within our traps. It is virtually impossible, however, to prevent other predators (for example, feral cats, bobcats, Cooper's hawks) from approaching cowbird traps. it is possible that simply close approach or harassment by one of these predators is sufficient to cause trapped bird mortality. Deceased BHCO are then easy "prey" as they lay on the mesh floor of a trap. Such events may help account for undetermined bird mortality during our trapping program. Problem #2: Vandalism Vandalism is often a significant problem encountered during cowbird trapping. Vandalism can have serious effects to cowbird trapping, in particular if the vandalism results in the destruction of Fourth Annual Report -2001 9 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. November 2001 traps and/or attempts to release trapped animals and bait birds. Despite its isolated situation, Macario Canyon is a heavily traveled riparian corridor. Migrant workers pass through Macario Canyon on their way to work in the surrounding agricultural fields. The canyon bottom is occasionally used for recreational purposes (running, mountain biking, motorcycle riding, and recreational off-road vehicle use; I. Quon, T. Myers, personal observation). Because of this, human activity (especially foot traffic) in the vicinity of some cowbird traps was frequent. The potential for vandalism was, correspondingly, high. However, despite these unauthorized uses of the canyon, we documented no vandalism in 2001. Several reasons probably contributed to the absence of vandalism. One reason is that all five of the traps were placed in open glades but hidden within or behind dense riparian vegetation. In addition, we posted signage in English and Spanish on each trap that described the purpose of and authority by which trapping activity was carried out. These signs may have also discouraged vandalism. Awareness that we had cowbird traps in the canyon was probably highest among the migrant workers, many of whom live in lean-tos and huts within the canyon. Their tenuous position in southern California society and desire to minimize self-attention probably played a significant role in precluding the incidence of trap vandalism at this site. Year 2002 Recommendations Based on our 2001 trapping experience at Macario Canyon and our concurrent experience with other trapping programs conducted in San Diego County, the following recommendations are made for the year 2001 trapping season. Trapping techniques, methods and general location of traps employed in 2001 should be used again in 2002. Ongoing assessment of trap condition and success should be continued. This may lead to the relocation of traps within Macario Canyon from year to year or within a field season. Possible reasons for relocation include but are not limited to harassment of trapped birds, declining or differential success of traps, and vandalism. Fourth Annual Report -2001 10 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. November 2001 When possible, especially when and if new traps must be constructed for a project, we strongly recommend modified "mega-traps". Mega-traps are large, rectangular traps modified from Australian crow traps by elimination of a double-peaked construction. Because of their rectangular shape these traps are more difficult for avian predators to access, and their use seems to result in fewer incidents of "unexplained" mortality. The trapping period should remain at 123 days from approximately 15 March (weather permitting) to 20 July. Conclusion Our previous data document a notable decrease in the number of cowbirds observed and trapped in Macario Canyon between 1998 and 1999 (Varanus Biological Service 1998a, 1999). In 2000, the number of cowbirds trapped rose dramatically (Varanus Biological Services 2000) and in 2001 captures declined slightly. Nest monitoring results indicate there was no nest parasitism of LBVI in 2001. We did not observe other incidents of cowbird parasitism in Macario Canyon. We neither found cowbird eggs in LBVI nests nor host passerines (including LBVI) feeding juvenile cowbirds. Many of the trapped juvenile cowbirds were relatively old at the time of capture. Irrespective of the origin of the juvenile cowbird population, the numbers indicate that, at minimum, cowbird numbers may vary from year to year in any area, and that trapping through the middle of July is justified. Because of the small number of LBVI nest attempts in Macario Canyon it is impossible to determine the success of the Macario Canyon trapping program has on the Macario Canyon least Bell's vireo population. However, in our four-year study we have not documented any incidents of cowbird parasitism of least Bell's vireo. There are no historic nest monitoring data from the canyon thus there is no scientific basis for comparison. Recent records indicate poor breeding success for this species in Macario Canyon but fail to document the reasons for such. It is known that extremely high parasitism rates on numerous passerine species can occur in the absence of effective cowbird trapping programs. A single female cowbird can deposit between 40 and 80 eggs per season into host nests (Franzreb 1989, O'Connor 1984). This suggests that even brief interludes of reduced trapping may have serious impacts on potentially Fourth Annual Report -2001 11 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. November 2001 parasitized species. The vireo population in Macario Canyon is small (between 2 and 4 pairs maximally over the past 6 years), continued trapping is warranted and trap placement should continue to follow the guidelines established during the first three years of the program. Success of Least Bell's Vireo We recorded no incidents of nest parasitism on least Bell's vireo in 2001. We found a total of two nests constructed by one pair of vireos. Success at the second of the two nests resulted in the fledging of two young. The first vireo nest was abandoned prior to egg deposition. The reason for abandonment is unknown. Unlike the previous history of vireo pairs in the vicinity of Traps 1 and 2 (Varanus Biological Services 1998b, 1999) each nest was well constructed and sturdily suspended in native vegetation. Both nests were located in the North Mitigation site where the vegetation has rapidly grown tall and dense over a three-year period. The vegetative structure in consort with the placement of two BHCO traps has possibly contributed to the successful fledging of young in Macario Canyon in 2001. Trapping Limits Many of the late season non-target captures are juveniles. This strongly suggests the need to monitor all cowbird trapping programs to determine the optimal time period that maximizes removal of cowbirds but minimally endangers non-target species. At Macario Canyon,, adult cowbird trapping success drops off greatly toward the end of June. Juvenile BHCO capture peak in early to mid-July and then likewise fall off precipitously. Most captures in late July are non- target juveniles (Figures 2 and 3, note scale difference). These data continue to support the need to remove cowbird traps from riparian habitats when cowbird trapping success has declined. Fourth Annual Report-2001 12 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. November 2001 Literature Cited Franzreb, K. E. 1989. Ecology and conservation of the endangered least Bell's vireo. U. S. Fish and Wildlife Service. Biol. Rep. 89(1). 17 pp. Friedmann, H., L. Kiff, and S. Rothstein. 1977. A further contribution to knowledge of the host relations of the parasitic cowbirds. Smithsonian Contributions to Zoology. 235:1-75. O'Connor, R. J. 1984. The growth and development of birds. John Wiley & Sons, N.Y. 315 pp. 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. 1984. The birds of San Diego County. Memoir 13. San Diego Society of Natural History. 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 City Project No. 3184. Varanus Biological Services, Inc. 1998b. First annual report least Bell's vireo trapping program. Cannon Road Extension Wetlands Mitigation Project Macario Canyon, Carlsbad, San Diego County, California City Project No. 3184. Varanus 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 City Project No. 3184. Varanus Biological Services, Inc. 2000. Third annual report 5-year Brown-headed Cowbird Trapping Program. Cannon Road Extension Wetlands Mitigation Project Macario Fourth Annual Report-2001 13 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. November 2001 Canyon, Carlsbad, San Diego County, California City Project No. 3184. Whitfield, M. and C. M. Strong. 1995. A brown-headed cowbird control program and monitoring for the southwestern willow flycatcher, South Fork Kern River, California, 1995. California Department of Fish and Game. Bird and Mammal Conservation Program Report 95-4. 17 pp. Fourth Annual Report -2001 14 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. November 2001 a Third Annual Report 5-year Brown-headed Cowbird Trapping Program Cannon Road Extension Wetlands Mitigation Project Macario Canyon, Carlsbad, San Diego County, California City Project No. 3184 Report Prepared for the City of Carlsbad September 2000 [I Cowbird Trap in Macario Canyon, Carlsbad, California 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 Principal Investigators: Ingri S. Quon William E. Haas Introduction . The City of Carlsbad is required to implement a brown-headed cowbird (Molothrus ater, BHCO) trapping program in Macario Canyon. This program is part of the biological mitigation 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 (IJSFWS, Biological Opinion No. 1-6-97-F- 51). The focus trapping area for the program is the north end of Macario Canyon, Carlsbad, San Diego County, California. The canyon is characterized by hillsides of native Coastal Sage Scrub and agricultural fields. Runoff from upstream development and the adjacent agricultural fields is sufficient to support Southern Willow Scrub and Southern Cottonwood-willow Riparian Forest habitat along the bottom of the canyon. Drainage from the canyon feeds into Agua Hedionda Lagoon at its northern end. The cowbird-trapping program is specifically designed to support recovery of the federally listed endangered least Bell's vireo (Vireo bellii pusillus, LBVI). Least Bell's vireos are small, insectivorous migratory songbirds of extremely limited range. Wintering in Baja California, Mexico, LBVI migrate northward to their breeding grounds in southern California between mid- March and early April. They typically nest in early successional willow-riparian habitats characterized by the presence of dense un erstory vegetation. Once widespread in low-elevation riverine valleys as far north as Tehama County in northern California, LBVI population numbers declined dramatically after the 1940's. Only since the onset of cowbird trapping and riparian habitat preservation and restoration have least Bells vireo populations begun to rebound. Two factors are primarily responsible for this species' demise and hence have contributed to its status as a federally listed endangered animal species: degradation (including loss) of southern California riparian habitat and brood parasitism by BHCO. The explosive increase in BHCO populations outside its historic range has accompanied the decline of riparian habitat. In southern California these two trends have concurrently contributed to the decline of numerous songbird populations in addition to the least Bell's vireo (for example, yellow warbler, Dendroicapetechia and warbling vireo, Vireo gilvus (Unitt 1984). Brown-headed cowbirds were. historically associated with buffalo and possibly antelope herds, and subsequently livestock, in the Great Plains of the United States. It is hypothesized that brood parasitism in BHCO evolved to accommodate the species' reliance on benefits gained foraging among herds of nomadic hoofed mammals. When the nomadic buffalo moved, cowbirds followed. Female cowbirds depositing eggs in other species' nest would potentially achieve the equivalent of "nest success" at the expense of parasitized hosts while allowing adult cowbirds to follow the buffalo herds. Brown-headed cowbirds have been documented using at least 130 bird species as hosts (Friedmann et al. 1977). Brood parasitism of least Bell's vireo by BHCO has been well documented. The history of brown-headed cowbird-least Bell's vireo interaction is summarized in Franzreb (1989). Trapping of BHCO using modified Australian Crow Traps is an accepted method of reducing brood parasitism in least Bell's vireo (Ibid.) as well as other riparian and non- riparian species (for example, southwestern willow flycatcher (Empidonax traillii extimus) Whitfield and Strong 1995). Between the early 1980's and 1990, cowbird parasitism of least Bell's vireo at Marine Corps Base, Camp Pendleton fell from 47 percent to less than 1 percent. . Third Annual Report -2000 1 5-year Brown-headed Cowbird Trapping Program Varanus Biological, Services, Inc. September 2000 Between 1986 and 1996, the Santa Margarita River vireo population on Camp Pendleton rose . from 68 pairs (98 territorial males) to 456 pairs (523 territorial males) (Fish and Wildlife Service 1998). Trapping programs along the Sweetwater River, San Diego River, and the San Luis Rey River in the vicinity of Oceanside have resulted in "similarly dramatic reductions in the rate of nest parasitism coincidental with implementation of cowbird control programs" (Ibid. p.34). Methods In 2000, Varanus Biological Services, Inc. (Varanus), under contract to Native Landscape, Inc., was responsible for implementing the third year of the City's cowbird trapping program in Macario Canyon. Cowbird trapping was performed under authorization issued to Varanus from both the USFWS and California Department of Fish & Game (CDFG). The contract specified a total of five traps (Figure 1). WGS84 117018'00 W "I ( /•' 'V. ..' ...: ii; •.sJ,,_.;; 41r lAa Hethonda Lagoon ra Tran ED Trap2a , P_t' 2bV - 2_4\L Trap 4b — Trap 3 \ - .. Y) Trap 5b). Trap 4a ) I Trap 5a [Macario Canyonj Z 0 0 cn 0 0 (v) S V WGSS4 1.1701800* W -a.- 0 1/2 1MILE TN -riIVIN I I - V '113Y° 0 1000 FEET 0 500m 1000w V Punted from TOPO' ©2000 Wildflower Productions (www.topo.com) FIGURE 1:2000 BROWN-BEADED COWBIRD TRAP LOCATIONS MACAIUO CANYON, CARLSBAD, CALIFORNIA In order to efficiently attract free-flying BHCO into cowbird traps it is usually best to provide each trap with an initial group of "bait birds". Song and activity of the bait birds are attractants to free-flying BHCO. Dairies, feedlots, livestock pastures and horse stables are all excellent sources from which to obtain bait cowbirds if trapping is done prior to cowbird dispersal into breeding habitat. Prior to initiating the trapping program we set up two cowbird traps at the Hollandia Dairy, San Marcos, San Diego County. Because of the density of BHCO at the dairy, we only Third Annual Report - 2000 V 2 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. September 2000 needed to supply the traps with an abundance of seed and water and began to trap cowbirds within 24 hours of trap set-up. The two dairy traps provided enough bait birds for all of the Macario Canyon traps. Because of potential bait bird loss from traps in Macario Canyon, Varanus maintained the feeder trap at the Hollandia Dairy through 12 April and then maintained a small colony of bait birds derived from these traps at a secure location through the end of the trapping season. Maintaining the colony ensured availability of an adequate number of bait birds throughout the trapping period in the event of vandalism or other events that reduced the number of bait birds in our traps. We deployed a total of five traps on 17 March. We placed them at regularly spaced intervals within the western portion of the canyon. Due to inclement weather, we initiated trapping on 18 March Activation of BHCO traps required baiting them with a minimum of two males and three female brown-headed cowbirds and supplying each trap daily with fresh water and seed. We wing-clipped (shortening the primary or flight feathers of the right wing) all bait birds to ensure that, in case of release due to vandalism or accidental escape, flight capability was severely impaired and potential breeding success greatly limited We posted a laminated sign on each trap describing the purposô and techniques of cowbird trapping The description.was posted in English and Spanish. Following activation, traps were checkeddaily to wing clip or remove and euthanize any new (i.e., newly trapped) cowbirds and release captured non-target species. During each visit, seed pans and water dispensers were cleaned and fresh seed and water added. To limit the attractiveness of traps to certain non-target species, especially seed-eating finches such as house finches (Carpodacus mexicana) from entering the cowbird traps we chose a seed mix composed primarily of white millet that did not include sunflower seeds. Because of harassment of our trap (bait and captured) BHCO by an adult female Coopers hawk and declining trapping success we relocated several traps late in the season. Traps 1 and 3 remained in place through out the trapping period. In late June: we moved Traps 2, 4, and 5 (initial locations designated as "a") to positions 2b, 4b, and Sb respectively (Figure 1). The cowbird-trapping program lasted a period of 124 calendar days. All traps were deactivated on 25 July, and dismantled and removed from the canyon on 2 August. All remaining bait and captured BHCO were euthanized at that time. Results We captured and euthanized a total of 81 BHCO as a result of this focused cowbird trapping effort (Table 1); 36 were adult males, 20 were adult females, and 25 were juveniles (young of the year). It was not possible to determine the origin (location) of juvenile cowbirds captured in Macario Canyon. All adult BHCO captures occurred prior to 1 July. All juvenile BHCO captures occurred after 30 June and began to decline by the middle of July (Figure 2). - We recorded no incidents of vandalism during the entire trapping regime. Ten wing-clipped individuals discovered means of egress from closed traps. Typically, when escapees are detected, . Third Annual Report -2000 3 5-year Brown-headed Cowbird Trapping Program • Varanus Biological Services Inc. September 2000 traps are closely inspected to determine the point of egress. When found the flaw is immediately repaired. During the Year 200 trapping program we detected no flaws. Of the 10 known, escaped individuals 7 returned to the traps. It is possible that harassment by accipiters may have caused some BHCO to attempt to escape by any means possible including attempts to exit, however improbable, via the same opening used for entering the traps. TABLE 1 Brown-headed Cowbird Trapping Results Macario Canyon, Carlsbad, California March - July, 2000 Category (Age and Sex) of Brown-headed Cowbird (BHCO) Captured Number (combined, all traps) BHCO captured - Adult female 20 BHCO captured - Adult male 36 BHCO captured - Juvenile 25 BHCO captured - Banded males 0 Net BHCO Captured 81 BHCO, Escaped, depredated, or otherwise Missing (based on wing-clipped individuals, including bait birds and/or captured birds, no vandalism involved). 10 BHCO, Escapees recaptured (known from clipped wing) 7 Net loss from traps 3 Trapped BHCO euthanized 78 We have documented that Cooper's hawks (Accipiter. cooperii) and sharp-shinned hawks (Accipiter striatus) cause cowbird mortality within cowbird traps. We have observed Cooper's hawks "working" the BHCO traps by scaring trapped cowbirds from the bottom of the traps into the apical corners of the trap, grabbing the cornered bir& with talons and then decapitating them as prey. The Cooper's hawks may succeed in removing the head only, or may be able to pull the entire carcass through the wire mesh leaving telltale feathers attached to the wire grid. They may also extract fallen carcasses if the cowbirds fall sufficiently close to the edge of the trap. Non-target Species We recorded a total of 205 non-target bird (that is, non-BHCO) captures in Macario Canyon cowbird traps in 2000 (Table 2). California towhee (Pipilo crissalis, n138) was the most frequently trapped non-target species, followed by song sparrow (Melospiza melodia, n49) and S Third Annual Report - 2000 4 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. September 2000 - / . - V• V• VV - -?'- -, .- VVV V tLikJiHJUi : El Males : ILl Females 0 Juveniles 18- 16- Z4- OR 0- house finch (Carpodacus mexicana, n=16). One each of the red-winged blackbird (Agelaius phoeniceus) and sharp-shinned hawk was also captured (Figure 3). We found two California towhees deceased in traps (both, recognized on the basis of feather wear had been captured almost daily throughout the season). Frequency of non-target captures was highest in the early part of the trapping season, depressed in May and June, and began to rise again in mid-July. This pattern is typical for cowbird trapping programs and is usually related to breeding success of locally breeding avian species. Many of the late season non-target captures are juveniles, especially of house finch, California towhee and spotted towhee. Figure 2: Number of Brown-headed Cowbird Caught Per Month 18 March through 25 July, 2000 Macario Canyon, Carlsbad, San Diego County March April May V• June July Month Non-avian species V No non-avian species were found in the traps during the trapping regime. It is highly probable that unobserved predators entered and escaped from traps. Potentially occurring predators are long-tailed weasels '(Mustela frenata), woodrats (Neotoma spp.), deer mice (Peromyscus spp.) and black rat (Rattus rattus). All have been observed inside cowbird traps (W. Haas field notes). In 2000 we suspected long-tailed weasels to be harassing cowbirds at several Macario traps. We found a weasel den and family in the vicinity of Trap 3 in 1999 (W. Hans field notes). We frequently found tracks in the vicinity of traps 1 and 2. Ground squirrels (Spermophilus beecheyi), house mice (Mus musculus) and several species of Peromyscus including deer mice (Peromyscus maniculatus) and cactus mice (P. eremicus) did enter -the traps, but usually only to Third Annual Report - 2000 5 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. September 2000 access the readily available seed. Fecal pellets from murid rodents were frequently found in and fl around seed pans in all Macario traps during the 2000 program. Figure 3: Number of Non-target Species Caught Per Month 18 March through 25 July, 2000 Macario Canyon, Carlsbad, San Diego County 100 90 80 Ow 70 c60 50 . 40 .. 30 20 z10 0 E] Non-targets March April May Jue • July Month Problems Two potential problems were anticipated for cowbird trapping in Macario Canyon and strategies were implemented to address them. Each problem is addressed individually and solutions or minimization strategies are suggested. Problem #1:, Depredation A large number of potential cowbird predators inhabit Macario Canyon. Predators detected in or around the cowbird traps since this project's inception include Cooper's hawk, sharp-shinned hawk, long-tailed weasel, ground squirrel, coyote (Canis latrans), bobcat (Lynx rufus), feral cat (Felis catus), black rat, southern pacific rattlesnake (CrotUlus viridis helleri) and Argentine ant (Linepithema hum ile). We confirmed cowbird depredation by an accipiter on 29 March when a juvenile sharp-shinned hawk was discovered in Trap 4 with the partial remains of a female cowbird. The sharp-shinned hawk, a California Department of Fish and Gathe Species of Special Concern was removed, banded, and released by William E. Haas using FWS band # 812-25320 (Size 2). The hawk was a second year male in juvenile plumage (Figure 4). To dissuade rodents from entering cages and possibly killing or injuring target or non-target birds, we placed birdseed in galvanized metal or plastic 4" (high) X 14" (diameter) pans. Locating traps to avoid contact with willow branches helped deter Argentine ants. Unfortunately, this introduced species of ant is omnipresent in most riparian habitats in southern California and Third Annual Report - 2000 - 6 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. September 2000 - difficult to exclude. They typically invade all cowbird traps to some degree. They seek out water guzzlers, but limiting the number of ants entering traps helps trapped birds avoid them as they drink. TABLE 2 Non-target Species Captured During Brown-headed Cowbird Trapping Macario Canyon, Carlsbad, California March - July, 2000 Non-target Species (Scientflc Name) Total Number Trapped Total Deceased/ Depredated Deceased California towhee (Pipilo crissalis) 138 2/0 House finch (Carpodacus mexicana) 16 0/0 Song sparrow (Melospiza melodia) 49 0/0 Red-winged blackbird (Agelaius phoeniceus) 1 0/0 Sharp-shinned hawk (Accipiter striatus) 1 0/0 Total Non-target Captures 205 2 Percent Non-target Loss (% Mortality) 0.9% It is, virtually impossible, however, to prevent other predators (e.g., feral cat, bobcat, Cooper's hawk) from approaching cowbird traps. It is possible that simply close approach or harassment by one of these predators is sufficient to cause trapped bird mortality. Such events may account for undetermined bird mortality during a trapping regime. At least one BHCO depredated in Macario traps in 2000 was due to the above-mentioned sharp-shinned hawk. Problem #2: Vandalism Vandalism is often a significant problem encountered during cowbird trapping. Vandalism can have serious effects to cowbird trapping, in particular if the vandalism results in the destruction of traps and/or attempts to release trapped animals and bait birds. Despite its isolated situation, Macario Canyon is a heavily traveled riparian corridor. Migrant workers pass through Macario Canyon on their way to work in the surrounding agricultural fields. The canyon bottom is occasionally used for recreational purposes (running, mountain biking, motorcycle riding, and recreational off-road vehicle use I. Quon, T Myers, personal observation). Because of this, human activity (especially foot traffic) in the vicinity of some cowbird traps was frequent. The potential for vandalism was, correspondingly, high. However, despite these unauthorized uses of the canyon, no vandalism was documented during the Year 2000 trapping season. Several reasons probably contributed to this phenomenon. One reason is that 3 of the traps were hidden in open glades but hidden within or behind dense riparian vegetation. In addition we posted signage in English and Spanish visibly on each trap that described the purpose of and . Third Annual Report -2000 7 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. September 2000 authority by which trapping activity was carried out These signs may have also discouraged vandalism. Awareness of the cowbird traps was probably highest among the migrant workers, many of whom live in lean-tos and huts within the canyon Their tenuous position in southern California society and desire to minimize self-attention probably played a significant role in precluding the incidence of trap vandalism at this site Year 2001 Recommendations Based on our 2000 trapping experience at Macario Canyon and our concurrent experience with other trapping programs conducted in San Diego County, the following recommendations are :made for the year 2001 trapping season. 1 Trapping techniques, methods and general location of traps employed in 2000 should be used again in 2001 2 Ongoing assessment of trap condition and success should be continued..,This may lead to the relocation of traps within Macario Canyon Possible reasons for relocation include but are not limited to harassment of trapped birds, declining or differential success of traps, and vandalism 3 The trapping period should remain at 123 days from approximately 20 March (weather permitting) to 20 July.: Conclusion - Our previous data documented a notable decrease in the number of cowbirds Observed and trapped in Macario Canyon during 1999 compared with 1998, a, decline from 78 to 37 total captures (Varanus Biological Service 1998a, 1999) In 2000, the number of cowbirds trapped rosel back to 1998 levels. Unfortunately we cannot equate the increase in numbers, especially the number of juveniles trapped, with any phenomena we observed within Macario Canyon Nest monitoring results indicate there was no nest parasitism of LBVI in 2000. Nor did we observe other incidents of cowbird parasitism in Macario Canyon such as cowbird eggs in nests or of host passerines feeding juvenile cowbirds. Many of the juvenile cowbirds were relatively old at the 'time of capture, and although young of the year, many were undergoing pre-basic molt when first trapped Irrespective of the origin of the juvemle cowbird population, the numbers indicate that, at minimum, cowbird numbers may vary from year to year in any area,: and that trapping through the middle of July is justified Because of the small number, of LBVI nest attempts in Macario Canyon it is impossible to determine the success of the Macario Canyon trapping program has on the Macario Canyon least Bell's vireo population. However, in our.three-year study we have not documented any incidents of cowbird parasitism of least Bell's vireo. There-are no historic data confirming nest parasitism in the canyon thus there is no scientific basis for comparison. Recent records indicate poor breeding success for this species in the canyon but fail to document the reasons for such. It is known that extremely high parasitism rates on numerous passerine species can occur in the absence of effective cowbird trapping programs. A single female cowbird can deposit between 40 and 80 eggs per season into host nests (Fraiizreb 1989, O'Connor 1984). This suggests that even brief interludes of reduced trapping may. have serious impacts on potentially Third Annual Report - 2000 . ' •' :' , , 8 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. . September 2000 parasitized species. The vireo population in Macario Canyon is small (between 2 and 4 pairs maximally over the past 5 years), continued trapping is warranted to assure the breeding success of this population. Trap placement appears to have been effective and therefore should continue to follow the guidelines established during the first three years of the program. Success of Least Bell's Vireo We recorded no incidents of nest parasitism on least Bell's vireo in 2000. We found a total of two nests constructed by one pair of vireos. One of the two nests resulted in the fledging of two young. The first vireo nest was abandoned prior to egg deposition. The reason for abandonment is unknown. Unlike the previous history of vireo pairs in the vicinity of Traps 1 and 2 (Varanus Biological Services 1998b, 1999b) each nest was well constructed and sturdily suspended in native vegetation. Both nests were located in the North Mitigation site where the vegetation has rapidly grown tall and dense over a three-year period. The vegetative structure in consort with the placement of two BHCO traps have no doubt contributed to the successful fledging of young in Macario Canyon in 2000; Trapping Limits Many of the late season non-target captures are juveniles. This strongly suggests the need to monitor all cowbird-trapping programs to determine the optimal time period that maximizes removal of cowbirds but minimally endangers non-target species. At Macario Canyon adult cowbird trapping success drops off greatly toward the end of June. Juvenile BHCO captures peak in early to mid-July and then fall off precipitously. Most captutes in late July are non-target juveniles (Figures 2 and 3, note scale difference). These data continue to support the need to remove cowbird traps from riparian habitats when cowbird-trapping success has declined. Figure 4. Second year male sharp-shinned hawk (Accipiter striatus) in BHCO Trap S Third Annual Report - 2000 9 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. September 2000 References and Literature Cited Fish and Wildlife Service. :1998. Draft recovery plan for the least Bell's vireo. U.S. Fish and Wildlife Service, Portland, OR. 139). Franzreb, K. E. 1987. Endangered status and strategies for conservation of the least Bell's vireo (Vireo belliipusillus) in California. W. Birds 18:43-49. Franzreb, K. E. 1989. Ecology and conservation of the endangered least Bell's vireo. U. S. Fish and Wildlife Service. Biol. Rep. 89(1). 17 pp. Friedmann, H., L. Kiff, and S. Rothstein. 1977. A further contribution to' knowledge of the host relations of the parasitic cowbirds Smithsonian Contributions to Zoology. 235:1-75. O'Connor, R.J. 1984. The growth and development of birds. John Wilcy & Sons, N.Y. 315 pp.. Salata, L. 1983. Status of the least Bell's vireo on Camp Pendleton, California U. S. Fish and Wildlife Service, Laguna Niguel, CA 62 pp Unpublished report Unitt, P. 1984. The birds of San Diego County. Memoir 13. San Diego Society of Natural History. . . . . Varanus 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 City Project No. 3184. 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 City Project No 3184 Varanus Biological Services, Inc. 1998b. First annual report least Bell's vireo trapping program. Cannon Road Extension Wetlands Mitigation Project Macario Canyon, Carlsbad, San Diego County, California City Project NO. 3184. . Whitfield, M and C. M. Strong. 1995. A brown-headed cowbird control program and monitoring for the southwestern willow flycatcher, South Fork Kern River, California, 1995. California Department of Fish and Game. Bird and Mammal Conservation Program Report 95-4. 17 pp. 01 Third Annual Report -2000 . . 10 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. September 2000 First Annual Report - 1998 5-year Brown-headed Cowbird Trapping Program Cannon Road Extension Wetlands Mitigation Project Macario Canyon, Carlsbad, San Diego County, California City Project No., 3184 Report Prepared for the City of Carlsbad 6 October 1998 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 Principal Investigators: Ingri Quon William Haas Introduction As part of the biological mitigation 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) the City of Carlsbad is required to implement a brown-headed cowbird (Molothrus ater, BHCo) trapping program. The focus trapping area for the program is the north end of Macario Canyon, Carlsbad, San Diego County, California. The canyon is characterized by hillsides of native Coastal Sage Scrub and agricultural fields. Runoff from upstream development and the adjacent agricultural fields is sufficient to support Southern Willow Scrub and Southern Cottonwood-willow Riparian Forest habitat along the bottom of the canyon. The drainage feeds into Agua Hedionda Lagoon at its northern end. Cowbird trapping is conducted in support of recovery of the Federally listed endangered least Bell's vireo (Vireo belliipusillus). Least Bell's vireo are small, insectivorous migratory songbirds of extremely limited range. Wintering in Baja California, Mexico, least Bell's vireo migrate northward to their breeding grounds in southern California between mid-March and early April. They typically nest in early successional willow-riparian habitats characterized by the presence of dense understory vegetation. Once widespread in low-elevation riverine valleys as far north as Tehama County in northern California, least Bell's vireo population numbers declined dramatically after the 1940's. Only since the onset of cowbird trapping and habitat preservation and restoration have least Bell's vireo populations begun to rebound. Two factors are primarily responsible for this species' demise and hence have contributed to its status as a Federally listed Endangered animal species: eradication and degradation of southern California riparian habitat and brood parasitism by BHCo. The explosive increase in BHCo populations outside its historic range has accompanied the decline of riparian habitat. In southern California these two trends have has concurrently contributed to the decline of numerous songbird populations in addition to the least Bell's vireo (for example, yellow warbler, Dendroicapetechia). Brown-headed cowbirds were historically associated with buffalo and possibly antelope herds, and subsequently livestock, in the Great Plains of the United States. It is hypothesized that brood parasitism in BHCo evolved to accommodate the species' reliance on benefits gained foraging among herds of nomadic hoofed mammals. When the nomadic buffalo moved, cowbirds followed. Female cowbirds depositing eggs in other species' nest would potentially achieve the equivalent of "nest success" at the expense of parasitized hosts while allowing adult cowbirds to follow the buffalo herds. Brown-headed cowbirds have been documented using at least 130 bird species as hosts (Friedmann etal. 1977). Brood parasitism of least Bell's vireo by BHCo has been well documented. The history of brown- headed cowbird-least Bell's vireo interaction is summarized in Franzreb (1989). Trapping of BHCo using modified Australian Crow Traps is an accepted method of reducing brood parasitism in least Bell's vireo (Ibid.) as well as other riparian and non-riparian species (for example, southwestern willow flycatcher, Empidonax traillii extimus; Whitfield and Strong 1995). Between the early 1980's and 1990, cowbird parasitism of least Bell's vireo at Marine Corps Base, Camp Pendleton fell from 47 percent to less than 1 percent. Between 1986 and 1996, the Santa Margarita River vireo population on Camp Pendleton rose from 68 pairs (98 territorial males) to 456 pairs (523 territorial males) (Fish and Wildlife Service 1998). Trapping programs along the Sweetwater River, San Diego River and the San Luis Rey River in the vicinity of Oceanside have resulted in "similarly dramatic reductions in the rate of nest parasitism coincidental with implementation of cowbird control programs" (Ibid. p.34). Methods In 1998, Varanus Biological Services, Inc. (Varanus), under contract to Native Landscape, Inc., was First Annual Report. 1998 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. Pted fmm TOPO! 0197 Wi1±ower Prodthn (ww.topoeoat) FIGURE 1 1998 BROWN-HEADED COWBIRD TRAP LOCATIONS MACARIO CANYON, CARLSBAD, CALIFORNIA responsible for implementing the City's cowbird trapping program in Macario Canyon. Cowbird trapping was performed under authorization issued to Varanus from both the USFWS and California Department of Fish & Game (CDFG). A total of five traps were required by this contract. Prior to initiating the trapping effort, one cowbird trap was established as a "feeder" at the Hollandia Dairy, San Marcos, San Diego County. Bait birds for the dairy trap were initially collected using mist nets under authority of Master Banding Permit #022761 issued to William E. Haas, Varanus' Principal Biologist. Mist-netted birds were then placed in the dairy trap as bait birds to attract sufficient cowbirds to supply all Macario traps. Dairies, feedlots, livestock pastures and horse stables are all excellent sources from which to obtain bait cowbirds if trapping is done prior to cowbird dispersal into breeding habitat. Because of potential bait bird loss from traps in Macario Canyon, Varanus maintained the feeder trap at the Hollandia Dairy through 30 May. Maintaining a trap at the dairy ensured availability of an adequate number of bait birds throughout the trapping period. A total of five traps, regularly spaced within the western portion of the canyon, were deployed on 19 March (Figure 1). Two traps were activated on 20 March with the remainder activated by 1 April when construction was completed. Activation of brown- headed cowbird traps required baiting them with a minimum of two males and three female brown- First Annual Report. 1998 2 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. headed cowbirds and supplying each trap daily with fresh water and seed. All bait birds were wing- clipped (cutting the leading edge of the one of each cowbirds' primary or flight feathers) to ensure that, in case of release or escape, flight capability is severely impaired and potential breeding success greatly limited. Each trap was also posted with a laminated sign on each trap describing the purpose and techniques of cowbird trapping. The description was posted in English and Spanish. Following activation, traps were checked daily to wing clip or remove any trapped cowbirds and release captured non-target species. During each visit, seed pans and water dispensers were cleaned and fresh seed and water added. To discourage certain non-target species from entering the cowbird traps, the seed mix of choice did not include sunflower seeds. The cowbird trapping operation lasted a period of 147 calendar days. All traps were deactivated on 25 August. All remaining BHCo were euthanized at that time. The traps were dismantled and removed from the site On 28 August. Results A total of 78 BHCo were euthanized as a result of this focused cowbird trapping effort (Table 1); 30 were adult male, 27 were adult female and 21 were juvenile (young of the year). It was not possible to determine the origin of juvenile cowbirds captured in Macario Canyon. These numbers do not include the 25 bait birds initially placed in traps. These, too, were euthanized at the end of the season. It is assumed that, based on time of year, the birds were locally fostered; if not within Macario Canyon then in nearby areas such as Agua Hedionda Creek. No incidents of vandalism were recorded during the entire trapping regime. At the beginning of the trapping program it was noted that seven individuals from Trap # 2 had discovered a means of egress from the closed trap. When the escapees were detected, close inspection of the trap indicated the point of egress was a deceptively sized hole in the wire mesh. It was promptly repaired and within one day, five of the escaped cowbirds (known from their wing-clipped condition) were recaptured. No additional incidents of escape were recorded during the remainder of the season. TABLE I BROWN-HEADED COWBIRD TRAPPING RESULTS MACARLO CANYON, CARLSBAD, CALIFORNIA MARCH - AUGUST, 1998 Number Captured Category (Age and Sex) of Brown-headed Cowbird (BHCo) Captured (combined, all traps) BHCo, Captured - Adult Female 27 BHCo, Captured - Adult Male 30 BHCo, Captured - Juvenile 21 Total BHCo Euthanized 78 Non-target Species A total of 225 non-target bird (that is, non-BHCo) captures were recorded in Macario Canyon cowbird traps in 1998 (Table II). song sparrow (Melospiza melodia, n83) was the most frequently trapped non- First Annual Report - 1998 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. target species, followed by California towhee (Pipilo crissalis, n=66) and house finch (Carpodacus mexicana, n=46). Only 5 individuals of non-target species were found deceased in traps; 2 deaths resulted from depredation (Cooper's hawk), 2 from weather related factors, and 1 of an unknown cause. TABLE II NON-TARGET SPECIES CAPTURED DURING BROWN-HEADED COWBIRD TRAPPING MACARIO CANYON, CARLSBAD, CALIFORNIA March - August, 1998 Non-target Species (Scientific Name) Total Number Trapped Total Deceased/ Depredated Deceased Black phoebe (Sayornis nigricans) 2 0/0 California thrasher (Toxostoma redivivum) 2 0/0 California towhee (Pipilo crissalis) 66 3/1 House finch (Carpodacus mexicana) 46 2/0 Red-winged blackbird (Agelaius phoeniceus) 6 0/0 Song sparrow (Mel ospiza melodia) 83 0/0 Spotted towhee (Pipilo macuI ata) 4 0/0 Western scrub-jay (Aphelocoma californica) 16 0/0 Percent Non-target Loss (Mortality) 225 5(2.2%) Non-avian species Three non-avian species were found in traps including southern Pacific rattlesnake (Crotalus viridis helleri), deer mouse (Peromyscus sp.) and Norway rat (Rattus norvegicus, Table Ill). Both the Norway rat and southern Pacific rattlesnake could have caused in-trap mortality. It is also highly probable that other unobserved predators entered and escaped from traps, and caused mortality in target and non-target species. Long-tailed weasels have been observed in traps along the San Luis Rey River (W. Haas, personal observation) extricating themselves from traps prior to entry by the trap technician. On one occasion in 1997, Hans had to capture and release an adult long-tailed weasel from a cowbird trap in Oceanside, CA along the San Luis Rey River. Long-tailed weasels were observed frequently in the vicinity of the Macario cowbird traps in 1998. TABLE III NON-AVIAN SPECIES CAPTURED DURING BROWN-HEADED COWBIRD TRAPPING MACARIO CANYON, CARLSBAD, CALIFORNIA MARCH - AUGUST, 1998 Non-avian Species (Scientific Name) Total Number Trapped Total Deceased Southern Pacific rattlesnake (Crotalus viridis helleri) 1 0 Deer mouse (Peromyscus sp.) I Norway rat (Rattus norvegicus) 1 1 First Annual Report - 1998 4 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. Problems Two potential problems were anticipated for cowbird trapping in Macario Canyon and strategies were implemented to address them. Each problem is addressed individually and solutions or minimization strategies are suggested. Problem #1: Depredation A large number of potential cowbird predators inhabit Macario Canyon. Predators detected in or around the cowbird traps included Cooper's hawk, long-tailed weasel, coyote (Canis latrans), bobcat (Lynx rufus), feral cat (Felis catus), black rat (Rattus rattus), Norway rat, southern Pacific rattlesnake and Argentine ant (Iridomyrmex humilis). Depredation and detection of (potential) predators was a frequent event throughout the trapping program. During one site visit M. Bache detected a Cooper's hawk attempting to pull a deceased cowbird through the trap wire. To dissuade rodents from entering cages to eat seed, and possibly kill and eat birds, seed was placed in galvanized 4" (high) X 14" (diameter) pans to keep seed confined. Clearing branches from around the traps so they could not use them as trails to the trap deterred Argentine ants. Unfortunately this introduced species of ant is omnipresent in most riparian habitats in southern California and difficult to exclude. They typically invade water guzzlers, but can be avoided by birds as they drink. It is virtually impossible, however, to prevent other predators (for example, feral cat, bobcat, Cooper's hawk) from approaching cowbird traps. It is possible that simply close approach by one of these - predators is sufficient to cause trapped bird mortality. Such events may account for the undetermined bird mortalities recorded during the trapping regime. Problem #2: Vandalism Vandalism is often a significant problem encountered during cowbird trapping. Vandalism can have serious effects to cowbird trapping, in particular destruction of traps and/or attempts to release trapped animals and bait birds. Despite its isolated situation, Macario Canyon is a heavily traveled riparian corridor. Migrant workers pass through Macario Canyon on their way to work in the surrounding agricultural fields. The canyon bottom is occasionally used for recreational purposes (running and mountain biking; I. Quon, M. Bache, personal observation) and a concrete dip at the northern end of the canyon is a popular locale for skateboarding activity. Because of this, foot traffic in the vicinity of some cowbird traps was relatively high. The potential for vandalism was, correspondingly, high. However, despite this heavy use of the canyon, no vandalism was documented during the 1998 trapping season. Several reasons probably contributed to this phenomenon. One reason is that traps were hidden in open glades within riverine vegetation. Traps left in the open, along roadsides or in other easily accessible locations offer an easy opportunity for vandals to perform quick and malicious work. In addition, signs in both English and Spanish posted visibly on each trap described the purpose of and authority by which trapping activity was carried out. These signs may have also discouraged vandalism. Awareness of the cowbird traps was probably most acute in the migrant workers, many of whom live in lean-to's and huts within the canyon. Their tenuous position in southern California society and desire to minimize self- attention probably played a significant role in precluding the incidence of trap vandalism at this site. 1999 Recommendations Based on our 1998 trapping experience at Macario Canyon and our concurrent experience with other trapping programs conducted in San Diego County, the following recommendations are made for the First Annual Report - 1998 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 1999 trapping season. Trapping techniques employed in 1998 should be used again in 1999. The trapping period should be established at 154 days running from 20 March to 20 July. Traps deployed in March this year immediately began to attract and catch BHCo. Earlier deployment might have benefited other parasitized bird species breeding in Macario Canyon, but it is rare that LBVi appear in southern California prior to mid-March, and rarely begin to breed prior to. 1 April. Toward the end of the season cowbird traps consistently removed cowbirds from the area until a substantial peak in captures occurred during the week of 12 July. Thereafter, captures declined to a maximum of only two birds per week and totaling only six birds for the remainder of the trapping period ending 25 August. During the same six-week period, between 6 and 15 non-target individuals were captured each week. Many of the late season non-target captures were juveniles. Though mortality for those captures was low this year, the potential to lose individuals of non-target species outweighs the limited benefit resulting from trapping after 15 July (6 BHCo in 185 trap-days between 19 July and decommission on 25 August). Conclusion It is too early to conclude whether the cowbird trapping program in Macario Canyon has had significant impacts on the Macario Canyon least Bell's vireo population. However, past research has shown that cowbird trapping may be the single most important factor leading to successful recruitment at a site. Extremely high parasitism rates can occur in the absence of effective cowbird trapping programs. A single female cowbird can deposit up to 40 eggs per season into host nests (Franzreb 1989; O'Connor 1984). This suggests that even brief interludes of reduced trapping may have serious impacts on parasitized species. No incidents of nest parasitism were recorded in 1998 despite six documented nest attempts by two different vireo pairs (4 attempts by one pair, 2 attempts by a second pair; Varanus 1998). Though Macario Canyon vireos were not successful in fledging young in 1998, the proposed restoration and mitigation projects currently underway are aimed at increasing the existing vireo population. First Annual Report - 1998 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. FIGURE 1 Number of Brown-headed Cowbirds Caught Per Week; 20 March through 25 August 1998 Macario Canyon, Carlsbad, San Diego County Macarlo Cowbird Trap Captures 01 Total MajesAwek Total Females/week RTc*at juvalweek Total Cowbirds/week 20 0 Total NT/week* 18 16 14 12 %LIkLL L 0 4-H 112 5 CD Date NT= Non-Target Species First Annual Report- 1998 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc. 7 Literature Cited Fish and Wildlife Service. 1998. Draft recovery plan for the least Bell's vireo. U.S. Fish and Wildlife Service, Portland, OR. 139pp. Franzreb, K. E. 1987. Endangered status and strategies for conservation of the least Bell's vireo (Vireo belliipusillus) in California. W. Birds 18:43-49. Franzreb, K. E. 1989. Ecology and conservation of the endangered least Bell's vireo. U. S. Fish and Wildlife Service. Biol. Rep. 89(1). 17 pp. Friedmann, H., L. Kiff, and S. Rothstein. 1977. A further contribution to knowledge of the host relations of the parasitic cowbirds. Smithsonian Contributions to Zoology. 235:1-75. O'Connor, R. J. 1984. The growth and development of birds. John Wiley & Sons, N.Y. 315 pp. Regional Environmental Consultants (RECON). 1986. Draft comprehensive species management plan for the least Bell's vireo ( Vireo belliipusillus). Prepared for San Diego Association of Governments, San Diego. 120 pp. plus appen. Regional Environmental Consultants (RECON). 1988. Draft revision: Comprehensive species management plan for the least Bell's vireo ( Vireo bellii pusillus). Prepared for San Diego Association of Governments, San Diego. 212 pp. plus appen. Salata, L. 1983. Status of the least Bell's vireo on Camp Pendleton, California. U. S. Fish and Wildlife Service, Laguna Niguel, CA. 62 pp. Unpublished report. Whitfield, M. and C. M. Strong. 1995. A brown-headed cowbird control program and monitoring for the southwestern willow flycatcher, South Fork Kern River, California, 1995. California Department of Fish and Game. Bird and Mammal Conservation Program Report 95-4. 17 pp. First Annual Report- 1998 5-year Brown-headed Cowbird Trapping Program Varanus Biological Services, Inc.