Broadly distributed west of the 104th meridian, the Western Tanager ranges farther north than any other tanager, breeding up to 60°N. At the northern limit of its distribution this tanager may spend as little as two months on its breeding grounds. Its broad occurrence in most open coniferous and mixed woodlands of western North America in the summer makes this species a quintessential element of western forests.
Despite the male's showy yellow-and-black plumage and red head and its strong, deliberate song, the species is not usually conspicuous. Indeed, the sluggish habits of the Western Tanager, which are highly reminiscent of the habits of vireos, and its predilection for the shade of foliage, generally keep it from view. During migration, however, large numbers may appear in city parks, orchards, and open areas.
The Western Tanager feeds predominantly on insects during the breeding season, but it also incorporates fruits and berries in its diet whenever it can. At other times of the year, fruits and berries constitute a substantial portion of the diet. Unlike the Scarlet (Piranga olivacea), Summer (P. rubra), and Hepatic (P. flava) tanagers, which deposit red 4-oxo-carotenoids in their plumages, the male Western Tanager deposits rhodoxanthin, a rare plumage pigment, in its red feathers. The species must rely on an external source of this pigment, unlike the aforementioned species, which produce red pigments from dietary yellow pigments. The source is presumably insects that have themselves acquired the pigment from plants.
With the exception of isolated studies on song structure (Shy 1984b), home range (Samuel et al. 1985), and pigmentation (Hudon 1991), little research has focused on the Western Tanager, and much of what is known of the species' breeding biology, behavior, and migration is anecdotal. This situation may be about to change, since several laboratories are now scrutinizing this species, on aspects as diverse as nest predation, brood parasitism, reproductive success, site fidelity, survi-vorship, and control of coloration. For the future, studies of breeding biology, including breeding systems, sexual selection, and vocal arrays, should prove rewarding.
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