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Annual continent-wide bird censuses, such as ���Ϲ���’s Christmas Bird Count and the U.S. Geological Survey’s Breeding Bird Survey, are priceless tools for conservationists, indicating which North American species are doing well and which aren’t.

But conservationists can’t always rely on the CBC or the BBS when it comes to nocturnal birds, secretive marsh dwellers, or species found in remote areas like the boreal forest. Instead, to get a sense of large-scale population trends for these hard-to-see species, they must painstakingly pore over monitoring data from various local counts.

As a team of researchers points out in a new study in , this is no easy task, since local counts often have different goals and protocols. Moreover, the data is often reported only to a small group of conservationists in the area. So, when the study authors wanted to examine the boreal birds of the upper Midwest and Northeast, they had to pull together several local counts—conducted by National Park, National Forest, and State Forest employees, as well as citizen science volunteers—and then control for differences in methods. From there they compiled a novel review of 14 avian species.

Of those species, seven showed significant population declines: the Olive-sided Flycatcher, Yellow-bellied Flycatcher, Gray Jay, Bicknell's Thrush, Magnolia Warbler, Blackpoll Warbler, and Evening Grosbeak. Many of these were previously considered common and stable, says Joel Ralston, an avian ecologist at the University of Massachusetts Amherst and the lead author of the study.

“There have been suggestions here and there that some of these species might be in trouble locally,” Ralston says. “But this is the first time that, on a broader regional scale, we can get a look at what the trends are.”

Though he isn’t yet sure why these seven species are struggling in the Midwest and Northeast, he notes that the boreal forest is under threat from development, logging, pest outbreaks, climate change, and air pollution. “Any of these factors, in addition to those faced during migration and on the wintering grounds, might be contributing,” the study notes.

Five other species, meanwhile, showed population increases. A particular surprise was the Swainson’s Thrush, which was thought to be undergoing a slight long-term decrease, based on BBS data. Ralston believes that Swainson’s Thrushes are moving to higher ground in the Northeast—where fewer people are available to count them—possibly as a result of climate change.

Geoff LeBaron, ���Ϲ���’s Christmas Bird Count director, praised the study as a complement to the BBS and the CBC. “It adds to our understanding of the whole picture,” he says. “It’s impossible to have one survey that covers all species well. You just can’t do it. There are too many competing needs.”

Most boreal habitat in North America lies in Canada and Alaska, but it juts down into the mountains of the Northeast and the boggy, lake-filled upper Midwest. (Ralston and his team looked only at the boreal birds in the latter two regions.) Very few paved roads run through the entire 1.2 billion acres of spruce, firs, and pine that make up North America’s boreal forest. As a result, birders must usually conduct surveys by foot of the roughly that breed there.

Those who want to dive into the backwoods and volunteer can try the northeast, run by the Vermont Center for Ecostudies every June. To find out more about boreal birds and to sign a petition to protect their habitat, visit the website of the campaign. This new initiative is advocating for at least 50 percent of the forest to be made off limits to development.