Courtesy Kenn Kaufman
Sage Sparrows breed in the Great Basin area of the western United States, ranging as far east as Wyoming and as far north as Washington. The species also breeds throughout California, both along the slopes of the Sierra Nevada and along much of the coast, and in coastal areas of northern and central Baja California. An endangered form of Sage Sparrow is found only on San Clemente Island, off the coast of southern California.
Numerous Important Bird Areas (IBAs) provide habitat for Sage Sparrow, including Washington's Fitzner-Eberhardt Arid Lands Ecology Reserve IBA (home to up to 200 birds), and California's Vandenberg Air Force Base IBA (host to 325 breeding pairs), San Clemente Island IBA, and San Diego National Wildlife Refuge IBA (home to one of the largest contiguous blocks of coastal sage scrub-breeding birds in the world).
The Sage Sparrow breeds in sagebrush over 90% of the time and is therefore considered an "obligate" species; that is to say, the Sage Sparrow is obliged to breed in this habitat type. It breeds in large patches brush, with a minimum requirement of about 320 acres of continuous habitat. Stands of other low desert scrub are sometimes used: bitterbrush, chamise chaparral, creosote bush, rabbit bush, saltbush, and shadscale. A mixture of bare ground and herbaceous plants appears to be an important component. Wintering birds use various semi-arid landscapes dominated by cactus, creosote bush, short native grasses, honey mesquite, and sagebrush.
The Sage Sparrow forages mostly on the ground by sight, plucking items from vegetation or gleaning them from the ground. The season and yearly rainfall patterns dictate the diet of this opportunistic species. The summer diet is omnivorous but favors insects: the larvae of beetles, crickets, grasshoppers, and moths as well as many adult insects, spiders, leafhoppers, and ants. Seeds are important year round, including grass, pigweed, and wild mustard.
Unlike most songbirds, Sage Sparrows often arrive on their breeding grounds already paired. The Bell's Sage Sparrow remains paired year round, but not necessarily with the same partner.
To defend its territory, the male Sage Sparrow sings from atop a shrub, twitching its tails as it sings. Fights, chases, and displays are also used to exclude others. Nesting occurs from March to July, with 1-3 clutches produce per year. The nest is usually set in a low shrub a few feet off the ground but is sometimes in a depression on the ground or a clump of grasses. As the male defends the site, the female builds a small cup with twigs and thick grasses and lines it with finer plant materials, then finally with feathers, fur, and hair.
Typical clutch size is three or four eggs, colored light blue, splotched and dotted with shades of brown. The female incubates them for about two weeks. The orangish yellow chicks are mostly naked, blind, and defenseless. Both parents probably feed small insects to the young, which leave the nest after about ten days. The chicks' fecal sacs are carried at least 45 feet from the nest, as a defense against predators, which include Townsend's ground squirrel and Common Raven. Juvenile Sage Sparrows form flocks before joining adults for migration.
The coastal populations of Sage Sparrow are non-migratory, as are birds found breeding across the southern parts of California, Nevada, and Utah. Birds in the northern part of the species' breeding range are short-distance migrants, spending the winter in Arizona, New Mexico, west Texas, southern California, and northern Mexico. Spring migrants arrive on the breeding grounds between March and early April. In the fall, small flocks of Sage Sparrows first move to short distances to molt and forage, before migrating south in September.