The California Thrasher is endemic to coastal and foothill areas of California, extending with the chaparral vegetation of the California Biotic Province (Raven 1977) into adjacent areas of northwest Baja California. It was first collected by the French navigator Jean-François de Galaup, Compte de La Pérouse, probably in 1786 at Monterey, central California, and published as “Promerops de la Californie Septentrionale.” This species was also found on Alejandro Malaspina's 1791 voyage to the Pacific Coast under the auspices of the Spanish court, and illustrated by his artist Jose Cardero (Duff 1961). More than 50 years later William Gambel, a protégé of naturalist Thomas Nuttall, accompanied an 1842 overland expedition to southern California via the Santa Fe Trail, and his “rediscovery” of the California Thrasher is reflected in its specific epithet, redivivum (meaning “resurrected”).
The California Thrasher is the largest of its genus. Although plainly colored, it is a striking and conspicuous bird, with its long and dramatically decurved bill, the dashing style in which it runs for cover with its long tail raised, and its habit of singing almost year-round, loudly delivering rich and colorful phrases from the tops of the tallest shrubs. It is common in dense chaparral; less so in adjacent oak woodlands, sage, and pine-juniper scrub; and of irregular occurrence in parks and gardens. Aided by long, sturdy legs, it feeds chiefly under cover on the ground by swinging its formidable bill in sideways arcs, digging vigorously and noisily in leaf litter (“thrashing” – hence the name) and peering intently into its excavations.
Although largely insectivorous during the extended breeding season (January–July), California Thrashers feed extensively on fruits during the drier seasons from late summer to winter, when they are more easily seen foraging about native and garden fruiting trees and shrubs.
The species is resident throughout its range. Individuals form long-term relationships; pairs are often found foraging and sometimes singing together. Territorial activity intensifies with the start of the winter rains, usually in November, and most pairs raise 2 broods between Feb and Jun. Eggs and young are susceptible to predation by Western Scrub-Jays (Aphelocoma californica); juveniles leave the nest running well but flying weakly, and many on suburbia's fringes are taken by cats. These predators, together with habitat loss to orchards, other forms of agriculture, and suburban development, are this thrasher's greatest threats.
Many features of the California Thrasher's suite of adaptive characters -- in morphology, ecology, and behavior -- are shared by ecological counterparts in scrubby habitats elsewhere in the world. In size and coloration, long tails and decurved bills, and in terrestrial foraging habits within scrubby vegetation, other birds that show similarities to the California Thrasher are babblers (Timaliidae: Pomatostomus) in Australia, certain Old World larks (Alaudidae: Alaemon, Chersophilus, Chersomanes), the Central American Queo (Thraupidae: Rhodinocichla rosea; Skutch 1962a), and especially the bandurillas (Furnariidae: Dumetaria) in Chilean matorral, the local equivalent to chaparral vegetation (Cody 1974, Cody and Mooney 1978).
This account relies heavily on a variety of natural-history reports by early California naturalists, including the classic study by Joseph Grinnell (Grinnell 1917b), and a single, detailed, breeding study conducted in suburban Pasadena over several seasons (Sargent 1940). The information is amplified by 3 decades of MLC's fieldwork (observations and cited papers on bird communities that are, here, largely ancillary in nature). From this literature, the distribution, density, habitat relations, and vocalizations are quite well known for the species, but comprehensive studies on banded populations are lacking, leaving questions on survivorship, dispersal, and nesting behavior at best incompletely answered.