Coastal California Gnatcatcher

Polioptila californica californica

Description

The coastal California gnatcatcher, Polioptila californica californica, is one of three subspecies of the California gnatcatcher. It is is a small, long-tailed bird that is dark blue-gray above and grayish-white below. The tail is mostly black above and below. The male has a distinctive black cap that is absent during the winter. Both sexes have a distinctive white eye-ring. Vocalizations of this species include a call consisting of a rising and falling series of three, kitten-like mew notes.

Behavior

Breeding occurs from mid-March through mid-May. Nests are composed of grasses, bark strips, small leaves, spider webs, down, and other materials, and are often placed in coastal sagebrush about 3 ft (0.9 m) above the ground. Clutch sizes average four eggs. Both males and females participate in all phases of the nesting cycle. Multiple broods in one season can occur but it is generally uncommon. Incubation lasts about 14 days and the chicks fledge in about 16 days. Juveniles are dependent upon or remain closely associated with their parents for up to several months following fledging. This sub-species is non-migratory.

Habitat

This species is found almost exclusively in the coastal sage scrub plant community with occasional occurrences in chaparral. The southern limit of its range coincides with the distributional boundary of this distinctive vegetation type. Coastal sage scrub vegetation is composed of relatively low-growing, summer (dry season) deciduous, and succulent plants. Dominant plant species include coastal sagebrush (Artemisia californica ), various species of sage (Salvia spp.), California buckwheat (Eriogonum fasciculatum ), lemonadeberry (Rhus integrifolia ), California encelia (Encelia californica ), prickly pear and cholla cactus (Opuntia spp.), and various species of Haplopappus. Within this plant community this bird can often be found in gullies, canyons, washes, and the lower parts of slopes.

Distribution

The coastal California gnatcatcher is restricted to coastal southern California and northwestern Baja California, Mexico from Los Angeles County south to El Rosario, Mexico, including the California counties of Los Angeles, Orange, Riverside, and San Diego. It was formerly found north to Ventura and San Bernardino Counties.

Most of the gnatcatcher populations occur on private lands. About 21% (81,992 of 393,655 acres; 33,181.1 of 159,307.2 hectares) of coastal sage scrub in southern California south of metro Los Angeles is publicly owned. About 64% or 52,500 acres (21,246.1 hectares) are on military reservations including Camp Pendleton Marine Corps Base, El Toro Marine Corps Air Station, Fallbrook Naval Annex, and Miramar Naval Air Station. Other publicly held lands are administered by the California Department of Parks and Recreation, the cities of San Diego and Lake Elsinore, the Southern California Metropolitan Water District, and the counties of Orange, Riverside, and San Diego.

Threats

The coastal California gnatcatcher has been extirpated from the California counties of Ventura and San Bernardino and is close to extinction in Los Angeles County. This bird has been eliminated from 42 sites occupied prior to 1960. These losses are the result of development (primarily for urban and agricultural uses) of the coastal sage scrub community this bird is dependent upon. Estimated losses in this habitat type are from 65-90% of the original range. The human population in southern California has increased dramatically during the last 20 years. Most of these people now live in areas along the coast that formerly supported the coastal sage scrub community.

The loss of coastal sage scrub vegetation has been associated with an increasing degree of habitat fragmentation, which reduces habitat quality and promotes increased levels of nest predation and brood parasitism, and ultimately, increased rates of local extinction. Fragmentation also isolates many populations threatening the genetic integrity of this species.

Conservation and Recovery

The U.S. Fish and Wildlife Service is currently participating in a study of gnatcatcher ecology in western Riverside County that was initiated in the spring of 1992. This study involves intensive monitoring of three color-banded gnatcatcher subpopulations occupying three different landscape settings. Preliminary results of nest monitoring activities in 1992 indicate that the birds that occupy small, fragmented patches experienced high levels of nest parasitism by cowbirds and only one of 15 nests fledged a total of two young. Gnatcatcher nests on the grazed patch were also heavily parasitized and only two of 25 nests fledged a total of four young. The gnat-catchers in the more natural setting had only one case of cowbird parasitism (one of 26 nests) and good reproductive success (11 of 26 nests fledged a total of 40 young). These findings strongly suggest that the adverse edge effects noted in fragmented forest habitats occur in shrubland communities as well.

Contact

U.S. Fish and Wildlife Service
Regional Office
Eastside Federal Complex
911 N.E. 11th Ave.
Portland, Oregon 97232
http://pacific.fws.gov/

Reference

U.S. Fish and Wildlife Service. 30 March 1993. "Endangered and Threatened Wildlife and Plants; Determination of Threatened Status for the Coastal California Gnatcatcher." Federal Register 58 (59):16742-16757.