California Gnatcatcher

Polioptila californica

B. Moose Peterson, US Fish & Wildlife Service
  • POLIOPTILINAE
  • 77,000

This species limited range, extending north from Mexico's Baja California to coastal southern California, and its specific habitat requirements, make it vulnerable and a high conservation priority. Burgeoning human populations have fragmented and destroyed suitable habitat for this species in southern California so that it was Federally-listed as a Threatened species in 1993.

Identification
A small, slender, gray, nonmigratory songbird having a long, black tail with white tips and fine white edging. Male in breeding plumage has a black cap, otherwise has a black line over the eye. Males mostly gray with darker upperparts. Females have more of a brown tone on back, flanks, and belly. Makes a kittenlike mewing that distinguishes it from the Black-tailed Gnatcatcher (Polioptila melanura). The California can also be distinguished from the Black-tailed by its darker underparts and less white on its tail. The other gnatcatchers, Blue-gray and Black-capped, are larger with more white on their tails.

Distribution and Population Trends
The entire world's population of the California Gnatcatcher occurs in Baja California and coastal southern California year-round where it depends on a variety of arid scrub habitats. Limited to coastal sage scrub habitat in California and northern Baja but more widespread in southern Baja. Even in the early 1900's, the population was described as being scarce and irregularly distributed but by the 1940's habitat was noticeably reduced. In the U.S. loss of coastal sage scrub habitat has been estimated to be as much as 70-90%, with approximately 33% lost since 1993 when the species was Federally-listed as Threatened.

Ecology
Monogamous pairs tend to stay in the same locale. Both parents build nest, incubate, and care for young. Nest site established by male who also initiates nest building. The cone-shaped nests are built in shrubs and first-brood eggs (2-5) are laid in late March. With a roughly 120 day breeding season, they may be able to have as many as three broods per season. A high rate of nest predation is compensated by up to ten re-nesting attempts over the long breeding season. Young tend to disperse within ten km of their natal territory and find a mate within several months. Survival depends on winter temperatures and rainfall. Main food intake consists of arthropods, especially leafhoppers, spiders, beetles, and true bugs.

Threats
With the description of the California Gnatcatcher's preferred habitat type coinciding with the description for high real estate value (coastal, low-elevation, shallowly sloped or level lands), it is no wonder that habitat loss is the main threat facing the species. Coastal sage scrub habitat was developed rapidly from the 1940's to 1990's for agriculture, grazing, or urban areas, and is considered now one of the most endangered habitats in the U.S. This has created a tenuous relationship between the U.S. and Mexico; 99% of the population survives south of El Rosario, Baja California. Habitat loss is not a concern in central and southern Baja California. Parasitized by Brown-headed Cowbird in northern part of its range where the cowbirds begin laying the first week in May, some 2 months after gnatcatchers begin. Some gnatcatchers may abandon nest after cowbird egg laid. Exotic plants outcompete native coastal sage scrub plants after fires or grazing. Apparently can withstand disturbance at nest site during incubation from researchers and loud noise (construction, airport, highway). In the U.S., the Threatened status and protection afforded to the northernmost subspecies may be reevaluated by the USFWS under pressure from developers because of recent genetic findings.

Conservation
The northernmost subspecies was listed in 1993 as Threatened in California under the Endangered Species Act. This decision instigated legislation in California that protects natural communities while allowing continued economic growth. The implementation of this initiative, known as the Natural Community Conservation Planning (NCCP) program, continues to hinge on the conservation of the California Gnatcatcher. To date, 6 NCCP plans have been approved, conserving 36,279 coastal sage scrub habitat. In 1995, a California Gnatcatcher Symposium was held at which research findings were shared, though much of the work remains unpublished and not peer-reviewed. Most habitat used by the gnatcatcher is under private ownership. In 2000, the U.S. Fish and Wildlife Service designated 13 critical habitat units, encompassing 207,890 ha, 83% of which was on private lands. Survey protocols have been standardized and long-term monitoring programs implemented to answer research needs and evaluate the effectiveness of some management efforts. Cowbirds are trapped in areas inhabited by gnatcatchers. Habitat restoration is also done as a mitigation effort by developers. It usually takes 4 years for California Gnatcatchers to return and begin nesting at a restored site. The removal of exotic plants is one method used to restore habitat.

What Can You Do?
Audubon's Important Bird Area program is an essential tool for the conservation of California Gnatcatchers as well as other species. To learn more about the Important Bird Areas program in California, and to learn how you can help with the IBA program visit: http://iba.audubon.org/iba/viewState.do?state=US-CA

The Endangered Species Act has helped protect the California Gnatcatcher and made it possible to learn critical information about its biology. Audubon continues to work to ensure that this vital legislation is being used to protect our publicly-owned wildlife resources. Check out http://policy.audubon.org/endangered-species-act to learn of the latest news about the Endangered Species Act and how you can help. To learn more about other species protected under this legislation, visit: http://endangered.fws.gov/

References
Atwood, J. L. and D. R. Bontrager. 2001. California Gnatcatcher (Polioptila californica). In The Birds of North America, No. 574 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D.C.