The Center for Biological Diversity, Santa Clara Valley Audubon Society, Defenders of Wildlife, San Bernardino Valley Audubon Society, California State Park Rangers Association, and Tri-County Conservation League submitted a petition to list the California population of the western burrowing owl (Athene cunicularia hypugaea) as an endangered or threatened species under the California Endangered Species Act.

photo by Peter LaTourrette

The western burrowing owl is a small ground-nesting bird of prairie and grassland habitats, which in many areas has adapted to human-altered habitats as urban development and agriculture have eliminated natural grasslands. Burrowing owls in the western United States rely upon burrows dug by burrowing mammals for nests, primarily those of ground squirrels in California. Burrowing owls also require open fields with adequate food supply for foraging habitat, low vegetative cover to allow owls to watch for predators, and adequate roosting sites. These owls can often be seen perched or standing by their burrow or hunting insects, rodents, amphibians, or small birds in open fields. Nesting season is from February through August, with most pairs usually fledging 4 or 5 young. After the nesting season, most owls in California remain throughout the winter as year-round residents and owls from others areas augment resident California populations. Burrowing owls are susceptible to predators that can access their nest chamber, such as foxes, coyotes, skunks, raccoons, and snakes, and are also preyed upon by various other raptor species, such as hawks, eagles, and other species of owls.

Burrowing owls in California historically ranged throughout the Central Valley, were found in suitable habitat in coastal areas from Marin County south to the Mexican border, and sparsely inhabited desert areas in the northeastern and southeastern portions of the state. Densities of owls in some areas of the state have increased with intensive agriculture, such as in the Imperial Valley, southern Central Valley, and lower Colorado River Valley.

Once a widely distributed and common grassland bird, the burrowing owl has been declining significantly in California for at least the last half century. Although early accounts of the burrowing owl reported the species as "probably one of the most common birds in California" and "abundant," "common," or "fairly common" range-wide in California, the species has been in continuous decline throughout the state since at least the 1940s. Severe localized declines of owl populations were evident by the early 1900s, for example in the Fresno area, in the region of Los Angeles, and in Orange County. Urbanization corresponding with human population growth has eliminated or greatly reduced breeding populations from large areas where the owl was formerly common, such as in San Diego, Orange, Santa Barbara, Santa Cruz, and Santa Clara Counties.

The decimation of breeding owl populations in Orange and San Diego Counties is indicative of the fate of the species in urbanizing areas of the state. The burrowing owl was once "common everywhere" in coastal San Diego County, with one ornithologist noting that in the late 1860s "burrowing owls stood on every little knoll" around San Diego. Even as late as 1975, burrowing owls were described as "abundant" and "bordering on ubiquitous" in suitable habitat in Orange County and were considered a "regular component" of the coastal environment. By 2001 only 9 or less breeding pairs remained in the entirety of Orange and San Diego Counties.

Breeding burrowing owls have been extirpated from approximately 8% of their former range in California during the last 10-15 years. A comprehensive statewide survey conducted in the early 1990s revealed that breeding owls were entirely eliminated from 5 counties (Napa, Marin, San Francisco, Santa Cruz, and Ventura), and were nearing extirpation in 6 other counties (Sonoma, San Mateo, Monterey, San Luis Obispo, Santa Barbara, and Orange). Small breeding populations of owls have likely been extirpated from Humboldt and Mendocino Counties, southwestern Solano County, and western Contra Costa County as well, and breeding owls are rapidly disappearing from southern Los Angeles, western San Bernardino, western Riverside, and San Diego Counties.

Local extirpations of owls become cumulatively significant for the species as owl habitat is destroyed and owls are relocated from urbanizing areas. Burrowing owls have never been successfully reintroduced to a location where they have been extirpated, partly due to the owl's strong fidelity to burrow sites. Owls regularly reuse burrows from one year to the next, and for this reason are not easily forced to move to a different burrow, especially during nesting season.

photo by Peter LaTourrette

Based on a survey of the majority of the owl's range in California, an estimated 9,450 nesting pairs of owls remained statewide in the mid-1990s, exclusive of the deserts and Great Basin areas. Recent urban development has eliminated or displaced some of these birds. The number of breeding owl colonies located in the survey area throughout California declined nearly 60% from the 1980s to the early 1990s, and the statewide number of owls is currently thought to be declining at about 8% per year.

Over 71% of California's breeding owls currently live in the margins of agricultural land in the Imperial Valley, an area that comprises only 2.5% percent of the land area of the state. Owls in the Imperial Valley, which primarily nest in burrows in earthen irrigation channels, are facing threats from conversion of agricultural lands to urban development, plans to line earthen canals with concrete, and ground squirrel eradication programs. Over 15% of the state's breeding owls reside in the southern Central Valley, an area undergoing explosive human population growth and rapid conversion of agricultural lands to urban development.

California's remaining burrowing owls are threatened primarily by habitat loss to urban development, persecution of ground squirrels and other burrowing rodents, and intensive agricultural practices. The state-approved practice of relocation of owls from development sites is accelerating local extirpations from rapidly urbanizing areas, such as in Santa Clara County. Other factors contributing to the decline of owls statewide include destruction of burrows through disking and grading, impacts of pesticides, increased predation by non-native or feral species, habitat fragmentation, and other human-caused mortality from vehicle strikes, electrified fences, collisions with wind turbines, shooting, and vandalism of nesting sites.

There are currently no state or federal laws that protect owl habitat and such habitat is rarely purchased by agencies for public lands. An estimated 91% of all owls remaining in California occur on private land, most of it under enormous development pressure. Although federally designated as a Species of Special Concern in 1994, federal regulatory mechanisms such as Habitat Conservation Plans have proved inadequate in protecting significant owl habitat or stopping the rapid decline of the species. State regulatory mechanisms, such as designation as a state Species of Special Concern in 1979, adoption of burrowing owl mitigation guidelines by the California Department of Fish and Game in 1995, state Fish and Game Codes protecting nesting raptors, and limited creation of mitigation banks to purchase habitat, have proved unsuccessful in protecting the burrowing owl and its habitat. The failure of owl conservation efforts in the San Francisco Bay Area is indicative of the limitations of attempts at regional and local conservation planning for non-listed species. To the detriment of burrowing owls, their management has been limited to project-by-project responses to development impacts, an approach that is inadequate for the long-term maintenance of the species in significant parts of its range in California.

Throughout the vast majority of the burrowing owl's range in California, breeding owls persist in only small, declining populations of birds that are highly susceptible to extirpation, as seen in the precipitous decline of owl populations in several areas of the state. The burrowing owl is in imminent danger of becoming extinct throughout a significant portion of its range in California, and requires immediate protection as an endangered or threatened species.

graphic Andrew Rodman ©2002
December 23, 2003
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