The boundaries of this EBA run from south-west Oregon (USA) through the coastal valleys and foothills of the Sierra Nevada mountains of California to north-west Baja California (Mexico). The 2,000-m contour has been used as the upper limit of the EBA, as the breeding ranges of all the restricted-range species lie between this altitude and sea-level.

The climate is Mediterranean, characterized by cool, wet winters and dry, warm or hot summers. General vegetation types include montane coniferous forest, oak forest, mixed evergreen forest, chaparral (a dense scrub 1-3 m high with many endemic plant species), coastal scrubland, grassland and riparian habitats. Overall, nearly 50% of plant species are endemic to this region (WWF/IUCN 1997).

All the restricted-range species occur in chaparral and/or coniferous-oak forest, apart from Agelaius tricolor, which nests in large colonies in marshes.

This is a large EBA and the restricted-range species are not found throughout. Of the two most restricted species, Selasphorus sasin breeds in a narrow coastal strip from south-west Oregon through California and winters south to Mexico, with non-migratory populations on some of the offshore islands and much of the southern Californian coast. Pica nuttalli is only found in the coastal valleys and foothills of central California. The remaining species are more widespread in California and north-west Baja California, but are still judged to have breeding ranges of less than 50,000 km² and so qualify as restricted-range.

Two other species, Anna's Hummingbird Calypte anna and Wrentit Chamaea fasciata, are also largely confined to this region, but are judged to exceed the range limit, and have therefore been excluded. California Gnatcatcher Polioptila californica, sometimes considered conspecific with the widespread Black-tailed Gnatcatcher P. melanura, occurs in Baja California as well as in southern California and has also been excluded on range size.

There are many subspecies in this region which are clearly delimited and are candidates for elevation to full species rank in the near future (K. L. Garrett in litt. 1997). Examples are Bell's Sage Sparrow Amphispiza (belli) belli, which is found in coastal sage scrub and chaparral from north-west California to north-west Baja California, and Santa Cruz Jay Aphelocoma (coerulescens) insularis (already treated as a species by some authorities), which is restricted to Santa Cruz Island in the Channel Islands.

California is the most heavily populated state of the USA, and the extent and character of the natural vegetation almost throughout this region have changed dramatically in the last two centuries, a process which has included the loss, fragmentation and degradation of many wetlands and riparian and coniferous woodlands. For example, there has been a 91% loss of wetlands (due to filling and draining for urban and agricultural growth), an 89% loss of riparian woodland (due to agricultural and urban development, and river canalization and diversions), a >90% loss of native perennial grassland (through urbanization, conversion to agriculture and a conversion to non-native annual grassland mediated by overgrazing), and a >30% loss of the most diverse conifer forests (through conversion to less diverse forest-scrub, montane chaparral, and clear-felled areas (WWF/IUCN 1997).

Despite the destruction, the EBA's restricted-range species are relatively common within their remaining habitat, and none is considered threatened. There is, however, one very high-profile, non-restricted-range, threatened species which occurs in this EBA: California Condor Gymnogyps cali fornianus (classified as Critical), historically widespread but having declined rapidly throughout the twentieth century owing to direct persecution and accidental lead ingestion from carcasses, so that in the mid-1980s the remaining eight wild birds were captured to join other zoo-held stock in a captive-breeding recovery programme. In April 1997 the total population stood at 118 birds, of which 92 are in captivity at the San Diego Wild Animal Park and World Center for Birds of Prey, and 26 are in the wild, including five in northern Arizona, 17 near Cuyama valley in the Santa Barbara County region, and four in the Ventana Wilderness Area at Big Sur (L. F. Kiff in litt. 1997). Another much publicized bird is Spotted Owl Strix occidentalis (classified as Near Threatened), which relies on mature coniferous and mixed coniferous-oak forest along the Pacific coast of Canada, USA (including in this EBA) and Mexico.

There are many protected areas in this region (estimated to cover c.11%). Of particular note is Yosemite National Park (3,083 km2) in the Sierra Nevada, one of the most visited national parks in the USA, although the great majority of this park land is above 2,000 m. Others include the Channel Islands National Park (1,001 km²), various coastal sage habitat reserves in Orange and San Diego counties, and Redwood National Park (424 km²), which is a World Heritage Site.

Recommended citation
BirdLife International (2024) Endemic Bird Area factsheet: California. Downloaded from https://datazone.birdlife.org/eba/factsheet/1 on 23/11/2024.