In birding as in life, the most satisfying accomplishments often require the most effort. Adding Bicknell’s Thrust to your life list is one of those high effort – high reward milestones.

Seven members of the thrush family nest in Maine. These species are Eastern Bluebird, American Robin and five species of thrushes with various amounts of spotting on their breast. These spot-breasted thrushes are among the finest of avian songsters. Their flute-like songs are ethereal, in part owing to the fact that these thrushes can control the left and right side of their syrinx, the organ that produces sound in birds. Thrushes can harmonize with themselves!

The Wood Thrush is more common to our south, but can reliably be found throughout the state. Veeries occur throughout the state. The Veery sings a song that spirals downward in pitch. The common name of this thrush comes from its characteristic call note, Veer. Swainson’s Thrush, whose song spirals upward rather than downward like the Veery’s song, is a bird of spruce-fir forests. This species is therefore scarce in the southern third of Maine. Hermit Thrushes are widely distributed in the state, nesting in bogs as well as conifer forests. The final species, Bicknell’s Thrush, is the least known of our thrushes and is restricted to high elevations.

Bicknell’s Thrush has only been recognized as a full species for the past two decades. It was formerly considered a subspecies of the widely distributed Gray-cheeked Thrush, which occurs from Alaska to Newfoundland in boreal habitats. Owing in large part to the work of the late Henri Ouellet, formerly of the Canadian Museum of Nature in Ottawa, the American Ornithologists Union elevated Bicknell’s Thrush to a new species.

Ouellet demonstrated that Bicknell’s Thrush is a valid species with several lines of evidence. He began by showing that Bicknell’s Thrushes differ subtly in the color of the upperparts, the tail feathers, the throat and the undersides from Gray-cheeked Thrushes. Bicknell’s are lightly smaller than Gray-cheeked’s.

To really make his case, Ouellet needed to demonstrate that the two forms are reproductively separate. He analyzed the songs of Gray-cheeked and Bicknell’s Thrushes, finding distinct differences. Furthermore, Bicknell’s Thrushes on their breeding grounds did not respond to playbacks of Gray-cheeked Thrushes. We see a similar situation with Alder Flycatcher and Willow Flycatcher. The two species are virtually dead ringers for each other but give distinctive songs. Females of one species do not respond to the songs of the other.

Ouellet’s final piece of evidence was a comparison of the DNA of the two forms. The analysis showed that the DNA differed by an amount similar to differences between other closely related species. The analysis suggested that the ancestral group split into Gray-cheeked Thrush and Bicknell’s Thrush about a million years ago.

The nesting range of Bicknell’s Thrush includes the Adirondack region of New York, and portions of Vermont, New Hampshire, Maine, Nova Scotia, New Brunswick and Quebec.

In northern New England, Bicknell’s Thrushes are generally found above 3000 feet in elevation. Bicknell’s Thrushes like stunted spruce-fir forest, particularly areas that have been disturbed by fir waves or rime ice accumulation during the winter. They may nest along the edge of ski trails. The thick re-growth of these disturbed areas is often nearly impenetrable, necessitating patience if you want to see one of these birds.

Male Bicknell’s Thrushes sing until the middle of June and then singing stops abruptly. Early morning is the peak singing time so camping out in proper habitat or hiking up before dawn is wise. You see what I mean by high effort! In short, if you want to see a Bicknell’s Thrush on its breeding habitat in Maine this year, you better plan a trip soon.

[First published on May 31, 2015]