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Study Maps And Estimates Population Of Rare Songbird

Bicknell's Thrush incubating a nest on Stratton Mountain,Vermont
K.P. McFarland
Vermont Center for Ecostudies
Bicknell's Thrush incubating a nest on Stratton Mountain,Vermont

The Bicknell’s Thrush summers on the highest peaks of the Adirondacks and Green Mountains.  A new study released by the Vermont Center for Ecostudies has found their population is one of the smallest of any migratory songbird in the U.S. and Canada.
The abundance map and study of the Bicknell’s Thrush estimates there are about 71,000 of the birds breeding in the high mountain evergreen forests of the Northeast.  The study uses data collected by citizen scientists since 2011.  Conservation biologist and study lead author Dr. Jason Hill says because they are limited geographically, finding the birds is manageable. But, since they are uncommon, detecting and counting them is difficult.   “In the study we used data from almost 750 different sampling  locations across New England and those sampling stations are visited by citizen scientist volunteers who are experienced birders and counting birds in a very specific statistical framework to allow us to be able to calculate these kinds of population estimates.  And often they hike up the night before and they get up at 3:30 the next morning and at specific locations that are the same from year to year on these hiking trails they count the birds. Probably close to 95 percent of the observations are heard only. And they have a distinct song that make them very instantly recognizable.”

The study found that about 85 percent of the Bicknell’s Thrush population is on conserved land.  Of that, more than half is in New Hampshire’s White Mountain National Forest, Maine’s Baxter State Park and the Adirondack High Peaks Wilderness area.  Again Dr. Hill:  “At the moment we don’t have an idea exactly of does survivorship or reproductive output for this species does it differ between protected areas and unprotected areas?  We just don’t know that. This study we just identified the high proportion of Bicknell’s Thrush that occur on protected lands. In New England you often find Bicknell’s Thrush at the high elevations nesting right along the ski runs.  I mean just meters off the ski runs sometimes. On the wintering grounds that’s a very different story.  We think the species almost entirely over-winters in the Dominican Republic. And there human encroachment on the wintering habitat is probably the biggest threat to Bicknell’s Thrush.”

The Bicknell’s Thrush is known to nest on Whiteface Mountain. The Army’s 10th Mountain Division out of Ft. Drum trains on the mountain. The Adirondack Council spokesman John Sheehan says the group has challenged proposed development plans and worked with the military regarding exercises near the bird’s habitat.    “We know that there are Bicknell’s Thrushes nesting on Whiteface Mountain and that’s been a habitat for quite some time now.  But these maps help to confirm that there is habitat spread out throughout a great deal of the Adirondack Park and that this habitat continues to be threatened even though it is the best protected of the bird’s habitat anywhere in North America.”

Sheehan adds that while much of the Bicknell’s Thrush habitat in the Adirondacks is on the Forest Preserve and therefore won’t be developed, the bird still faces threats like acid rain and climate change.   “Forever Wild is one very good layer of protection for this bird here in New York and it’s even better than the land use controls that are in place in other locations.  But we also have to worry about what’s coming out of the sky both in terms of acid rain and climate change.  Over time climate change can shrink the Krummholz Zone that these birds live in, the area of the stunted trees that are the last place the trees can live up on mountain summits. This is essentially a forest that can’t take an awful lot more abuse that it already has to handle on a regular basis. So climate change and acid rain will have a real impact on living things and this is one of the ones that is in most danger.”

Study Link: "The potential winter distribution and the U.S. breeding range, population estimate and abundance for Bicknell’s Thrush"

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