By Lee Franks
The vocal repertoires of birds are among the richest in the animal kingdom. Vocalizations convey information about the identity, location, and motivation of the singer, including ownership of territorial space. More varied song repertoires help attract females and foster superiority in vocal duels between competing males.
Vocal mimicry (one species being copied by a second species) is one way some species increase the size of their vocal repertoire. Selection has favored a large and diverse repertoire in some species and one way of increasing repertoire size and diversity is to incorporate sounds from the surrounding acoustic environment, even sounds that do not belong to the birds’ own species, as well as non-avian sounds such as the barking of dogs, screeching of machinery, or human whistling. The most renowned vocal mimic is the Northern Mockingbird, but the California Thrasher, a striking and exuberant songster, is certainly a close second.
The California Thrasher (Toxostoma redivivum) is a 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 coyote brushes found in the chaparral sections of Edgewood Park.
A medium-sized to large (12″) songbird that is nearly twice the weight of the Northern Mockingbird, and 10% heavier than the American Robin. The bird is similar to the California Towhee in overall coloration. Its upper-parts are chocolate-brown, while its under-parts are a rich buff. The chin and upper throat are pale, and there is a faint pale eyebrow. Their bill and legs are black.
Walks or hops between foraging stops on the ground. Runs swiftly, with long tail raised. Often seeks cover with a dashing run. Climbs through vegetation to gain an elevated song perch, or access a nest. Eats insects and other arthropods such as beetles, spiders, and crickets, which are taken on the ground. They locate prey by digging vigorously with their long bills in leaf litter and in soft ground beneath cover. When they eat plant food it is usually poison oak and toyon. Mated individuals often feed on the ground near each other, as do parents and dependent young.
The California Thrasher is strongly territorial. Both male and female defend territories. Territory borders are often disputed with neighbors. Strong agnostic interactions occur between this thrasher and Western Scrub-Jays, which are potential nest predators.
The California Thrasher commonly mimics a wide range of avian species that share its habitat, as well as frogs, coyotes, and a postman’s whistle. They loudly deliver their repertoires from elevated perches, allowing as many as 8 neighboring territorial thrashers to be heard at the same time in the dense chaparral canyon on the south side of the Clarkia Trail (upper section).
The female also sings “loudly and sweetly,” and a mated pair may counter-sing for extended periods. Male and female songs appear the same in quality, content, and volume. This thrasher sings year-round, but with varied vigor and intensity through the seasons. (Listen to some songs here.) Songs are heard more or less continuously throughout the November to June period, and with declining frequency after breeding through the summer. They are quietest in late summer (molting period), but singing frequency increases around mid-August, corresponding to completion of molt. Singing further increases in frequency in the fall, and becomes more extended and vigorous after the first rains of the season (mid–to late-November).
The California Thrasher’s breeding season is of extended duration (February through June). They typically lay a first clutch (generally 3 to 4 eggs) in February or March. Their second brood follows immediately after the first, with the female laying a second clutch while the male is still feeding the dependent young of the first brood.
Both parents build their nests, incubate the eggs, and brood the young. The young depart the nest at 12 to 14 days old, with well developed legs enabling them to run, but with notably short wings, with flight feathers about half grown. The last 30% of their adult weight is gained out of the nest. The young birds remain in parental territories for 3 to 4 months.
The Birds of North America, No 323, 1998 Martin L. Cody
Ornithology, 1990 Frank B. Gill
Photos by Tom Grey, http://tgreybirds.com/