The Center for Biological Diversity filed a formal notice of intent on Tuesday to sue the U.S. Fish and Wildlife Service for failing to make a decision on the Center’s 2010 petition to protect the Bicknell’s thrush as an endangered species. The thrush breeds only high in the mountains of the Northeast and eastern Canada, including Maine, New Hampshire, Vermont and New York. As with many mountaintop species, climate change threatens to push the thrush’s habitat right off the top of the mountain.

“Scientists predict that 98 percent or more of Bicknell’s thrush habitat in the United States could disappear with climate change,” said Mollie Matteson, a conservation advocate at the Center’s Northeast office. “Without swift government action, this icon of our wild Northeast mountains is on track to disappear in our lifetimes.”

Bicknell’s thrushes are olive-brown, migratory birds that nest in dense, coniferous forests near timberline in the Northeast and also breed in Quebec and Canada’s Maritime provinces. Scientists identified them as a distinct species in 1993.

Last summer the Fish and Wildlife Service acknowledged in a “90-day finding” that the Bicknell’s thrush may warrant protection as an endangered species. By law the Service must produce a final “12-month” decision a year after a petition is filed. That decision is now more than a year overdue, and the thrush was not included in the Service’s multiyear species-recovery work plan released this fall, meaning review of the species’ status has essentially stopped.

The overriding threat to the Bicknell’s thrush is climate change. Widely accepted climate models show the species’ breeding habitat shrinking dramatically in the Northeast. If the climate of the Northeast warms by approximately 6 degrees Fahrenheit, the bird’s habitat in the United States will virtually disappear. Scientists have already documented annual population declines of up  to 19 percent in parts of the bird’s range.

“Last year was the warmest year on record in the United States, with record storms, drought and fires. The disappearance of a plucky brown bird nesting at the tops of mountains may not be as dramatic, but all these events point to a world increasingly hostile to life as we know it,” said Ms. Matteson. “Our fate is not separate from that of the thrush or of other species at risk from climate change, and we need to start acting like we know that.”