The Townsend's Solitaire is widely distributed in western North America, where it is more closely associated with high mountain country than is any other thrush species save the Mountain Bluebird (Sialia currucoides). From the time it was first collected, by John Kirk Townsend along the lower Willamette River, Oregon, in 1835, the solitaire has often been overlooked. Even Townsend shot only a single individual, although this specimen proved sufficient for John James Audubon to honor Townsend in naming and describing the species in 1838 ( Mearns and Mearns 1992a ).
In summer, the Townsend's Solitaire haunts a variety of montane coniferous forest types, up to and even above tree line. In autumn, it descends to lower elevations, spreading outward from the mountains into adjacent foothills and valleys and wintering in juniper (Juniperus sp.) woodlands or other habitats that provide abundant fruit. Most populations appear to make only a short altitudinal migration between summer and winter grounds, although northern breeders migrate longer distances southward for the winter. In a few areas the species is resident year-round.
The sober gray plumage of adults does not change with the seasons and is identical in males and females, set off only by a white eye-ring and subtle, partially concealed markings of buff on the wings and white on the outer tail feathers. In marked contrast to its inconspicuous appearance, this species has an elaborate and salient song, which is widely extolled as “one of the most glorious and beautiful of bird songs” (A. Saunders, quoted in Bent 1949 ), an “infinitely fine and sweet rendering of mountain music...in rippling cadences” ( Hanford 1917 ). Despite this reputation, the song is surprisingly little studied.
During the breeding season, males sing prominently on exposed canopy treetops, then drop into the forest understory to forage quietly with their mates. This solitaire's occasional habit of sallying for aerial insect prey, which it captures with an audible snap of the bill, is distinctive among thrushes and has provoked frequent comparisons to the behavior of tyrant flycatchers. Townsend's Solitaire nests on the ground beneath rocks, logs, or other objects that provide a sheltering overhang, and its proclivity for nesting on exposed dirt banks along road cuts makes breeding pairs easy to find in some areas. Although rarely parasitized by Brown-headed cowbirds (Molothrus ater), solitaire nests are frequently plundered by predators, and nest predation is the primary determinant of variation in reproductive success among individuals and populations. Adaptations to overcome the negative impact of nest predation include a long nesting season, beginning early in the summer, and the ability to renest multiple times in a season.
During the winter, individual birds of both sexes are strongly territorial, defending patches of juniper trees both intra- and interspecifically, and feeding largely or even exclusively on the junipers' ripe, fleshy berries for the entire nonbreeding season. Solitaires are conspicuous in fall and winter because of their frequent, loud songs and calls and their characteristic habit of perching on exposed treetops, which allows territory holders simultaneously to advertise ownership and to scan for intruders. Individuals engage in violent fights to establish and defend high-quality feeding territories, with adults enjoying significantly greater success in these skirmishes than first-winter birds; the outcome of this severe competition directly affects fitness, since owners of large, berry-rich territories survive the winter at higher rates than owners of small territories containing few berries.
Research on the Townsend's Solitaire has been uneven. Habitat usage, diet, and foraging behavior are reasonably well known, especially for the nonbreeding season. The defense of winter feeding territories has been thoroughly described and analyzed in initial studies by Salomonson and Balda ( Salomonson and Balda 1977 ), and Lederer ( Lederer 1977b , Lederer 1977a ), and in a long-term, detailed field study by Bowen ( Bowen 1995 ). Basic parameters of the nesting cycle and annual reproductive success have been measured by Shambaugh ( Shambaugh 1987 ) and Bowen ( Bowen 1995 ). But the solitaire's mating system, population dynamics, and other features of its breeding-season biology are little known. Its behavior during migration has not been studied at all.