Bicknell's thrush is a medium-sized thrush, at 17.5 cm (6.9 in) and 28 g (0.99 oz). One of North America's rarest and most localized songbirds, it breeds on coniferous mountain tops and disturbed habitats of northeastern North America. While very similar in appearance and vocalization to the gray-cheeked thrush, the two species, with two completely different breeding ranges, differ slightly in their morphology and vocalizations. It was named after Eugene Bicknell, an American amateur ornithologist, who made the first scientific discovery of the species on Slide Mountain in the Catskills in the late 19th century. John Burroughs, in his essay, "The Heart of the Southern Catskills" (1886), writes effusively about the voice of Bicknell's thrush heard near the summit on his climbs of Slide Mountain, and how on his stays on Slide saw them nowhere else but "about the summit", and saw no other thrush but Bicknell's.

The grey-cheeked thrush is a medium-sized thrush. This species is 15–17 cm (5.9–6.7 in) in length, and has the white-dark-white underwing pattern characteristic of Catharus thrushes. It is a member of a close-knit group of migrant species together with the veery and Bicknell's thrush; it forms a cryptic species pair with the latter. The grey-cheeked thrush is all but indistinguishable from Bicknell's thrush except by its slightly larger size and different song. The two were formerly considered conspecific. Of all the American spotted thrushes, the grey-cheeked has the most northern breeding range.