Swainson’s Thrush

The woodland thrushes in the genus Catharus are somewhat famous for replacing each other as elevation increases in the mountains of the Northeast. Veery is at the bottom, often in wetter forests, followed by Hermit and Swainson’s, with Bicknell’s restricted to the highest peaks (above 2500’). It is most closely associated with conifers over most of its New Hampshire range, thus overlapping broadly with the species above and below it in the mountains, but also occurs in low-elevation spruce fir in the north where it can be found with the occasional Veery as well.

Like all these thrushes, Swainson’s is usually heard before it is seen, and its song possesses many of the same flutelike and ethereal qualities. It is best distinguished by the fact that it is the only one of the four whose song rises in pitch and does so in a manner typically described as “spiraling.” Another distinctive vocalization is its nocturnal flight call, which is a single note reminiscent of a spring peeper. If you hear a “spring peeper” overhead at night in May or September, it’s actually a Swainson’s Thrush passing by on its migration to or from South America. If seen, the most reliable field mark for this species is its bold buffy eye ring.

Available data on Swainson’s Thrush population trends in the Northeast are highly variable, and the New Hampshire graph shown here is a good example of the larger regional uncertainty. Trends to our north often show long-term or recent declines, sometimes followed by a leveling off, while the species seems to be increasing in Pennsylvania. The latter is unusual because the typical pattern is for northern species to respond to climate change by shifting northward or upslope, and the latter has been noted in some local studies of montane bird communities. If such a shift becomes more pervasive there is concern that Swainson’s Thrush may displace the rarer Bicknell’s.