California Thrasher Life History

Habitat

The California Thrasher is a flagship species of the chaparral, a shrubby habitat found only in California and a small part of Baja California. This plant community features shrubs and small trees, most below about 13 feet tall. Key plants include chaparral whitethorn, buckbrush, ceanothus, chamise, toyon, coffeeberry, sugarbush, laurel sumac, holly-leaved cherry, lemonade berry, manzanita, and mountain mahogany. In the southern part of the range, smaller numbers nest in sagebrush habitats with California buckwheat, California sage, and coyotebrush. In the northern part of the range, and at higher elevations in the south, California Thrashers inhabit open woodlands of the chaparral transition zones, where trees such as golden-cup oak, blue oak, white oak, interior live oak, Douglas-fir, and pines (Jeffrey, Coulter, pinyon, and foothill pines) grow above the montane chaparral. California thrashers require underbrush with copious leaf litter, and do not inhabit open woodlands that lack it. Where chaparral approaches the Mojave Desert, California Thrashers breed in a mixture of scrub oak, Joshua tree, and California juniper and down into the juniper scrub, but they are replaced by LeConte’s Thrashers in desert with cactus species.

Food

During the rainy season, which coincides with the breeding season, California Thrashers eat mostly insects and other arthropods. They forage by sweeping the bill through the leaf litter and looking for prey, which they seize with a quick pounce. They watch the ground for movement and often excavate by probing and gaping (inserting the bill into the ground, then opening it). They eat larval and adult forms of ground-loving beetles, earwigs, isopods (sowbugs or roly-polies), millipedes, spiders, Jerusalem crickets, moths, ants, wasps, and bees. As fruit ripens in late summer, rains cease, and insects become scarcer, their diet includes more berries, including poison oak, toyon, elderberry, blackberry, manzanita, coffeeberry, cascara, laurel sumac, and mistletoe. In orchards and lush backyards, they also accept offerings of grapes, pomegranates, figs, persimmons, oranges, suet, meat, and bread crumbs.

Nesting

Nest Placement

Nests are set about 7 feet above the ground in dense shrubbery.

Nest Description

Both male and female construct the nest, a bulky platform of twigs that is lined with roots, stems, bark, forbs, and weeds. Nests measure on average 10 inches across and 5 inches tall, with interior cup about 4 inches across and 2 inches deep.

Nesting Facts

Behavior

California Thrashers form long-term pair bonds. Courtship behavior is hard to observe in their dense habitat, but seems to involve males chasing females, which perch, raise the tail and head, and flutter the wings. In the early part of the breeding cycle, females sometimes join their mates in song. Pairs regularly forage together year-round as well. Both male and female defend the territory, year-round, occasionally chasing or fighting neighboring pairs while giving low chup calls. Pairs typically raise two broods of young per year. The parents chase away the young of their first brood as they prepare to nest a second time, although the male sometimes feeds young from the first brood as the female builds a second nest. Territory size varies from about 6 acres in optimum habitat to more than 25 acres in less productive habitat.

Conservation

According to the North American Breeding Bird Survey, California Thrasher populations declined by about 1.6% annually between 1968 and 2015, resulting in a cumulative decline of 54% over that period. Partners in Flight estimates a global breeding population of 240,000, rates the species a 15 out of 20 on the Continental Concern Score, and includes it on the Yellow List for range-restricted species. If the current rate of decline continues, the species will lose another half of its population by 2050. As for most songbirds of chaparral, loss of habitat to clearing, development, and agriculture is the chief conservation threat that faces this species. Feral cats also kill and eat California Thrashers, particularly young birds. Because their territories tend to be large, California Thrashers often vanish when development causes habitat to be fragmented.

Credits

Cody, Martin L. (2012). California Thrasher (Toxostoma redivivum), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Lutmerding, J. A. and A. S. Love. Longevity records of North American birds. Version 2015.2. Patuxent Wildlife Research Center, Bird Banding Laboratory 2015.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2017). The North American Breeding Bird Survey, Results and Analysis 1966–2015. Version 2.07.2017. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, USA.

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