Ecologists find an avian mystery atop Stratton Mt.
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By Josh O'Gorman Rutland Herald - Published: July 14, 2008
STRATTON — Like a canary in a coal mine, an unusual bird found at the top of Stratton Mountain might be an indicator of climate change.
Since 1997, members of the Vermont Center for Eco Studies, based in Norwich, have come to Stratton to study the Bicknell's thrush — a medium-sized bird with a heavily spotted breast and a brown or olive-brown back. The birds spend most of the year on the Caribbean island of Hispaniola, but in late spring migrate to the mountaintops of the northeastern United States and Canada to breed.
The birds prefer to nest in the limbs of the balsam fir, which are found above 3,000 feet. At 3,936 feet, Stratton Mountain has an abundance of balsam fir trees that have long drawn Bicknell's thrushes and those who wish to study them.
Sarah Frey has spent the past six summers on top of Stratton Mountain studying the birds. This year, she and her colleagues from VCE arrived on May 21 and set up their mist nets — very fine nets that gently capture the birds and allow Frey and others to affix a band to the birds' legs and transmitters to the females. Weighing only a gram, the transmitters allow VCE's ornithologists to track the birds back to their nests, which are usually secluded in the densest parts of the mountaintop forest.
"They're very secretive birds in the field," Frey said.
For the past seven weeks, the VCE crew lived from Sunday to Thursday in the ski patrol hut at the mountain's summit, but Friday morning they took down their nets and began to pack up their gear.
During the course of their studies this year, they found something that has left them puzzled.
Chris Rimmer, VCE's director, said they have found a bird that appears to be a hybrid between the Bicknell's thrush and a veery, a bird usually found in marshlands at much lower elevations.
Rimmer said his colleague, Kent McFarland, was out counting birds — not all of them, but spending 10 minutes at a time at five different spots around the mountain — when he heard the song of a veery. Rimmer said the bird sang two or three veery songs, and then sang a song that began as a veery's but ended as the song of a Bicknell thrush.
Rimmer said they were able to capture the bird, which appears to have the physical characteristics of both a Bicknell's and veery, and drew blood to determine by DNA if it is a hybrid of the two.
"It has some genetic material or at least some behavioral material of a Bicknell's," Rimmer said.
Steve Parren, rare species expert for the state Fish and Wildlife Department, said the two birds are closely related.
"It's possible they have a common ancestor," Parren said. "You sometimes get some odd hybrids. Bobcats and lynxes have crossed, and that's odd because they don't overlap environments."
Like the lynx and the bobcat, the Bicknell's thrush and the veery do not overlap habitats either, and Rimmer said finding birds from low-lying habitats on top of the mountain might be an indication of climate change.
Rimmer said as the planet becomes warmer, trees that thrive at lower elevations will be found higher up the mountain. For every 1-degree change Celsius, forest zones will climb 500 feet, Rimmer said. With a 2-degree change, trees found at 2,000 feet will be found at 3,000 feet. The balsam fir, today found above 3,000 feet, will only be found above 4,000 feet, which will eliminate the Bicknell's habitat for much of the northeast.
"It's an indicator for us," Rimmer said. "The health of the thrush is a measure of the forests and all the other animals that live there."
Since 1994, Rimmer and others have traveled to Hispaniola to meet with environmentalists from Haiti and the Dominican Republic, the two nations that share the island.
"We think of them as our birds, but they spend less than half their time up here," Rimmer said. "A big part of our efforts is to train people down there to be good conservationists."
Rimmer said forests on the island have been decimated — less than 10 percent of the Dominican Republic's forests remain, and in Haiti only 1.5 percent.
Rimmer said ensuring the survival of the Bicknell's means preserving its habitats in the Northeast, where it's threatened by climate change, and in Hispaniola from deforestation.
As for the unusual bird, Rimmer said that DNA analysis is needed before he will be able to determine its significance as a sign of climate change.
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