“ …its shyness and seclusiveness, its habit of breeding in only the most inaccessible places, and its almost unbroken silence during most of the year have kept the taxonomic, distributional, and life-history facts concerning it in mystery so long that [the Gray-cheeked Thrush] has been correctly regarded as one of the least known of American passerine birds.” G. J. Wallace (1939: 218) 1
Breeding in taiga and low Arctic shrub thickets from Newfoundland to eastern Siberia, the Gray-cheeked Thrush is North America's least-known Catharus thrush. A furtive species, especially during spring and fall migration, with a strong affinity for tangled thickets, birders are more likely to hear this species' nocturnal flight call than to observe migrants on the ground. The Gray-cheeked Thrush is somewhat less retiring on breeding territories and during subarctic twilight periods, though most of its breeding range lacks road access and few ornithologists visit its remote breeding habitats.
During the breeding period the species shows considerable geographic overlap with four other thrushes, including two congeners—Swainson's Thrush (C. ustulatus) and Hermit Thrush (C. guttatus). Nesting habitats of these thrushes differ, however, with the Gray-cheeked Thrush primarily a bird of brushy willow-alder thickets, conifer scrub, and conifer forests with dense undergrowth.
The Gray-cheeked Thrush is similar in appearance to several other Catharus species, especially Bicknell's Thrush (C. bicknelli), which was not considered a distinct species from the Gray-cheeked Thrush until the 1990s (2). In fact, much of the published information on “Gray-cheeked Thrush” has been based on the work of Wallace (1) and Dilger (3, 4), who studied populations of Bicknell's Thrush. Arthur Cleveland Bent's Life Histories (5) devoted only 10 pages to the Gray-cheeked Thrush, compared to 18 pages for Bicknell's Thrush. Indeed, little quantitative research has been conducted on the Gray-cheeked Thrush, either on its breeding or overwintering grounds. Information on the species' breeding biology is limited largely to anecdotal observations, while only a handful of studies of its migration and overwintering ecology have been published. Consequently, the more comprehensive body of knowledge of the Bicknell's Thrush (see 6) often serves as a useful starting point for hypothesizing about the many unstudied aspects of Gray-cheeked Thrush behavior and ecology.
Recent analyses of population monitoring data have increased the urgency of improving our understanding of the Gray-cheeked Thrush. These assessments indicate that the once abundant Newfoundland population has undergone a precipitous decline since the 1980s, while this species is also experiencing a protracted decline on breeding grounds in northwestern North America. It is difficult to say whether losses are restricted to these regions, as monitoring data are extremely limited elsewhere. Clearly this is a species that deserves more attention from researchers and conservationists.