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Songbird’s decline fuels climate-change debate

Groups seek endangered-species status for Bicknell’s thrush



Contributing writer

The fate of a little bird that spends its summers in the high elevations of the Green Mountains could soon become a new focal point in a national battle over regulating climate-changing emissions.

Earlier this year, the federal government started the formal process for deciding whether to list Bicknell’s thrush, a rare songbird known for its flutelike call, as an endangered species. The U.S. Fish and Wildlife Service now is reviewing scientific material on the thrush, and an initial public comment period on the bird’s status ended Oct. 31.

The federal agency launched an initial yearlong review of the bird’s status after receiving a petition from the Vermont office of the Center for Biological Diversity, which contends that the Bicknell’s thrush needs protection under the Endangered Species Act. The process of being classified as endangered species could take far longer, however.

The brown, sparrow-sized bird nests at elevations about 3,000 feet in the mountains of northern New England and New York. Conservationists say that even with an endangered species listing, the threats faced by the Bicknell’s thrush could prove difficult to overcome. They warn that the bird faces extinction unless the U.S. government can slow climate change and greatly curb mercury emissions from Midwestern power plants.

Some environmentalists say that a recovery plan for the bird could require changes to the nation’s fossil-fuel-based economy – steps they contend the federal government is obligated to undertake under the provisions of the Endangered Species Act.

Mollie Matteson, a conservation advocate at the Center for Biological Diversity office in Richmond, Vt., said the Bicknell’s thrush has been faring poorly because of the shrinking of its already scarce habitat. The bird generally favors high-elevation nesting grounds on the timberlines of mountain ranges, including the Green Mountains of Bennington and Rutland counties.

Even in these mountainous areas, the bird seeks out a comparative sliver of land with just the right mix of balsam firs, suitable for nesting.

The bird’s habitat choices are shrinking dramatically because of climate change, Matteson said. Even if the climate warms by an average of 2 degrees, her organization estimates, the thrush’s habitat could shrink as much as 66 percent.

As the New England climate warms, environmentalists warn that hardwoods will overtake the firs on the alpine timberline, displacing the Bicknell’s thrush.

“It’s literally going to be pushed right off the mountain,” Matteson said.

Climate change won’t just affect the birds in the summer. The Bicknell’s thrush winters in tropical Caribbean forests, but climate change models predict those forests are going to become drier in the years ahead. That habitat is already facing degradation because of deforestation and development in Haiti and the Dominican Republic, Matteson said.

“Its wintering habitat is even more constrained than its breeding habitat,” she said.

The Bicknell’s thrush population also is likely faring poorly because of power plant emissions from the Midwest, said Jim Shallow, the conservation and policy director for Audubon Vermont. Blood samples collected from the birds in recent years have shown elevated levels of mercury, which could affect the reproductive health of the species, he said.

To save the bird, the federal government will need either to phase out coal power plants or install more scrubbing technology that would curb emissions. Either solution would be an expensive proposition, but Shallow argues they would be worth it because mercury emissions affect all species.

“There would be human benefits as well,” Shallow said.

Slow process expected

Few expect the process to evaluate Bicknell’s thrush to go quickly. Shallow warned it could take decades to determine whether to classify the species as endangered. One hurdle is that so little is really known about the bird.

Although Bicknell’s thrush was first documented in the late 19th century, it was long considered a subspecies of the Gray-cheeked thrush. Genetic testing finally confirmed the bird was a unique species in 1995. Scientists have known for years that the bird was in trouble, but they have needed to learn more about it before they could petition the government to protect it.

“We need to have a better handle on the life cycle dynamics for the bird,” Shallow said.

The government’s process for determining whether to protect the bird also will move slowly because of what is expected to be a monumental legal fight. An endangered species listing most likely would set the stage for environmentalists to sue to compel the U.S. government to tighten regulations on greenhouse gas emissions in general -- and mercury emissions in particular. If recent history is any indication, power plant operators and the federal government both would oppose such an effort because of the overwhelming costs involved, Matteson said.

“What needs to be done to save the species is enormous,” Matteson said.

The federal government so far has resisted arguments that it must regulate greenhouse gas emissions because of the Endangered Species Act. The Obama administration angered environmentalists earlier this year when it refused to incorporate greenhouse gas standards into a proposal to protect the endangered polar bear, and the Center for Biological Diversity previously sued the government for delaying the process of listing two threatened arctic seal species as endangered because the seals’ main threat would be climate change.

Fears that a bird will vanish

Although Matteson said she believes the Bicknell’s thrush is another species that can only be saved if climate change is addressed, not everyone is so sure.

Steve Parren, a zoologist at the Vermont Fish and Wildlife Department who coordinates the agency’s Wildlife Diversity Program, said he believes the argument that the birds will lose their timberline habitat because of climate change is a bit of a stretch.

Wind shear is just as important a factor as temperature in stopping hardwoods from overtaking firs on the ridgeline, he said.

Although Parren said he understands why environmentalists are focusing on the thrush to spark a conversation about climate change, he said the same case could be made for any number of animals. Environmental regulators are going to have a hard time mitigating climate change for all species, he added.

“It’s going to be fascinating in a horrible way,” Parren said.

What frustrates conservationists is that the Bicknell’s thrush was really only identified as a species fairly recently, and what is already known about the bird makes further study intriguing.

The little bird, for example, seems to favor open relationships and complex paternity situations, said Chris Rimmer, executive director of the Vermont Center for Ecostudies. The average Bicknell’s thrush nest of eggs often has two to four male birds caring for it, and both males and females have multiple mating partners. Genetic tests have proven that some males will care for fledglings that aren’t theirs, perhaps because of the confusion that comes with their polyamorous relationships.

This unusual arrangement has been brought about by necessity, Rimmer said. Males greatly outnumber females, and the species wouldn’t survive if monogamy were in fashion. The birds begin with a 50-50 gender ratio, but that number changes by the time they are old enough to mate. Although arrangements are open and cozy in the summer, males are much more territorial in the winter, and they will push the females to more degraded habitat. This means fewer females survive to summer, Rimmer said.

“Maybe they don’t make it north,” he said. “Maybe they arrive here in poor condition. You can get nasty storms in late May on mountaintops here.”

The Bicknell’s thrush has become a favorite among birders. Wayne Petersen, the director of Mass Audubon’s Important Bird Areas project, still fondly remembers when he and other birding enthusiasts would flock to Mount Greylock in the 1960s to catch the bird’s song in the deep dusk or early morning. Even then, birders knew the bird’s presence on the mountain was fragile and fleeting, inadvertently helped by a construction project that knocked the firs on the mountain back to an optimal height for nesting, Peterson said.

“It was really a toehold,” Petersen said. “It was something of an outpost.”

Thrush sightings petered out until they were gone from the mountain by the mid-1970s.

Now Peterson fears the same could happen for the bird in the rest of New England.

“It may come and go before we realize it, if we’re not careful,” he said.



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