Identity theft occurs with astonishing regularity in the avian world where all too often, species share so many overlapping traits as to appear virtually indistinguishable. Empidonax flycatchers are an excellent example of this phenomenon in North America, as are scaup. More esoteric, but no more simplistic, is the difference between Gray-cheeked and Bicknell’s Thrush.
Bicknell’s Thrush (Catharus bicknelli) was discovered as distinct from the established Gray-cheeked Thrush (C. minimus) back in 1881 when Eugene P. Bicknell visited New York’s Catskill Mountains. Considered merely a subspecies, Bicknell’s was finally peeled off Gray-cheeked by the American Ornithologists’ Union (AOU) in 1995. The birds were separated on the basis of differing songs, ranges, and physical characteristics, but DNA testing was most convincing, establishing that they probably diverged from a common ancestor about one million years ago. Still, these birds are so similar that most authorities state the two are not separable in the field. That’s not going to stop you though, is it? Here are some tips to tell Bicknell’s and Gray-cheeked Thrushes apart.
Both of these Catharus thrushes are olive-brown above with dark spots on a white breast washed with buff. This coloration extends through the underparts, though the spots do not. Gray flanks and pink legs round out the common description. If you encounter one of these birds in the field, distinguish it from the other spotted thrushes by plumage and face patterning. The Veery is cinnamon overall, while Hermit Thrushes flaunt those fetching rufous tails. Swainson’s Thrush is notable for its buffy eye ring and cheeks.
FACE: Both birds have gray cheeks, but Bicknell’s has more of an eye ring as well as brighter yellow at the base of the lower bill.
SIZE: One prominent physical distinction is that Bicknell’s is noticeably smaller than Gray-cheeked. A difference of 10% translates into almost an inch separating them, but since the birds are highly unlikely to stand shoulder to shoulder for you, compare to other available species. Bicknell’s also shows shorter wings with a shorter primary projection.
SONG: Some claim that these birds are easier to distinguish in the dark due to significant vocal differences. Their shared song consists of a jumbled series of notes, usually four phrases. In Bicknell’s, the song ends on a rising note, while the gray-cheek slurs that final note downward. Bicknell’s songs are typically longer than those of Grey-cheeked, averaging 2.45 seconds vs. 1.99. Also, Grey-cheeked do not typically sing a song type twice in succession. Here is a graphic comparison of the song of the two birds.
RANGE: Gray-cheeked Thrushes range widely, wintering in South America. They migrate through Central America as well as the Greater Antilles up into much of the eastern United States on their way to upper Canada and Alaska. They’ve even been spotted in Europe. Bicknell’s, on the other hand, is considered primarily a New England bird, though its breeding range actually extends from the Catskills where they were initially discovered up to the northern Gulf of the St. Lawrence. Bicknell’s also spends the colder months in the Greater Antilles with an estimated 90% of them wintering on Hispaniola.
ALTITUDE: This is actually a pretty fair way to distinguish between the two in the areas they overlap. Bicknell’s Thrush prefers mountaintop forests above 3000 feet. If you run into one of these birds high up in, say, the Adirondacks, chances are good that you’ve got a Bicknell’s.