HomeMy WebLinkAbout3184; CANNON ROAD WEST; RESULTS OF 1993 CALIFORNIA GNATCATCHER SURVEYS; 1993-09-20
P&D Environmental Services
A Division of PAD Technologies
1100 Town & Country Road
Suite 300
Orange, CA 92668
P.O. Box 5367
Orange, CA 92613-5367
FAX 714/953-6989
714/835-4447
September 20, 1993 An Employee-Owned Company
Mr. Frank Jimeno
City of Carlsbad
2075 Las Palmas Drive
Carlsbad, California 92000-4859
SUBJECT: Results of 1993 California Gnatcatcher Surveys for Reach 1 of the Cannon
Road Extension
Dear Mr. Jimeno:
Focused surveys to determine the potential presence of the California gnatcatcher (Polioptila
cahformca cahfornica) were conducted along the proposed Reach 1 extension of Cannon Road)
in the. City of Carlsbad. The project area runs parallel to and directly south of Agua Hedionda
Lagoon. On the west it begins where the existing Cannon Road terminates, approximately one
quarter mile east of the Interstate '5 freeway. The proposed alignment's eastern terminus is near
the mouth of Macario Canyon, approximately one mile east-of Interstate 5.
Introduction
The California gnatcatcher is 'a resident species in coastal and Riversidiân sage scrub plant
communities, especially-where dominated by California sagebrush (Artemisia californica) and
California buckwheat (Enogonum fasciculatum) It has a restricted range in the United States,
primarily limited to Orange, western Riverside and San Diego County. A small, isolated
population remains on the Palos Verdes Peninsula in Los Angeles County. This species is
generally found at elevations below 250 meters (800 feet) along the coast, and up to 250 to 500
meters' (800-1600 feet) at inland locations (Atwood 1990).
This species has undergone severe population declines in recent years As of 1990, populations
were estimated at approximately 1200 to, 2000 pairs of gnatcatchers (Atwood 1990). Reasons
for this species' decline have been attributed to loss and degradation of its preferred habitat, such
as by development, agricultural conversion, and fuel modification for fire control-. Thus, the
California gnatcatcher was proposed for listing as a federal endangered or threatened species in
September, 1991, and designated a federally threatened species in March,: 1993, by the United
States Fish and Wildlife 'Service (USFWS).
Mr. Jimeno September 20, 1993
City of Carlsbad Page 2
Methods
Survey methodology was discussed, prior tothesite visits,, with. Larry Salata of the USFWS.
A series of three visits to the site identified above were conducted by P&D ornithologist Doug
Willick on August 12, 19, and 27, 1993. Brian Daniels, also a P&D ornithologist, assisted with
the surveys on August 27. The surveys were conducted by slowly walking through all coastal
sage scrub (CSS) habitat located within the proposed grading limits, and as much as 1,000 feet
away from the grading limits where continuous suitable habitat was found. All bird species
observed or heard were recorded.
Gnatcatcher surveys were performed during morning hours, and under optimal weather
conditions for the detection of this species. These surveys were accomplished by ornithologists
with demonstrated experience in working with this species. A vocal technique commonly
referred to as "pishing" was occasionally used in an attempt to elicit a curiosity response in
birds. This technique will often coax the more inconspicuous varieties of birds into the open.
Results
The majority of the property affected by the proposed road extension is currently disturbed by
agricultural production. Moderate to high quality CSS habitat is found within the eastern section
of the alignment where it descends towards the mouth of Macario Canyon. California sagebrush
dominates the majority of this habitat. Pockets of mixed chaparral also occurs in association
with the CSS, especially on the north-facing slopes. Most of the sage scrub in the study area
occurs on the slopes west of Macario Canyon, with a small amount existing immediately east
of the Macario riparian habitat.
Five pairs of California gnatcatchers were found in the survey area. Two of the pairs were still
associated with fledged young, indicating the occurrence of successful nesting in the survey area.
It is presumed that all five pairs of adult gnatcatchers were on territory.
One pair was located in the two or three acres of CSS immediately east of the mouth of Macario
Canyon, and was usually observed within the proposed grading limits. A pair was present here
during the 1992 and 1993 least Bell's vireo (Vireo bellii pusillus) surveys. The remaining four
pairs were occupying sage scrub habitat on the slopes of several small drainages between
Macario Canyon and the agricultural fields.
It is not possible to accurately determine gnatcatcher territory boundaries, or home ranges,
without conducting color-banding studies and recording their movements during the breeding and
non-breeding seasons. It has been observed, for example, that gnatcatcher home ranges
generally decrease in size during the nesting season (Bontrager 1991). The observations made
during the focused gnatcatcher surveys, however, indicate that potentially four of the five
Mr. Jimeno September 20, 1993
City of Carlsbad Page 3
gnatcatcher pairs would be directly affected (e.g., have portions of their territories removed) by
the grading limits of the proposed Cannon Road extension. The remaining pair may be directly
or indirectly affected. Indirect effects may occur from disturbance related to construction noise
and startle effects, or by partial territory loss due to competition from gnatcatchers displaced by
the road extension.
Sincerely,
P&D TECHNOLOGIES
Doug 'il1ick
Biologist
REFERENCES CITED
Atwood, J.L. 1990. Status Review of the California Gnatcatcher (Polioptila californica).
Unpublished technical report, Manomet Bird Observatory, Manomet, Massachusetts.
Bontrager, D.R. 1991. Unpublished job report: Habitat requirements, home range and
breeding biology of the California gnatcatcher (Polioptila californica) in South Orange
County, California. Prepared for the Santa Margarita Company, Rancho Santa
Margarita, California; April 1991.
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