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Birds
On the Move

“There is something dreadfully wrong,” says duck hunter and Arkansas Wildlife Federation board member David Carruth, noting that many mallards stopped migrating south along the Mississippi Flyway several years ago. In a New York City suburb, Huntington Audubon Society president Stella Miller was surprised to see robins huddled in a crabapple tree during a snowstorm. What’s happening to the birds?

Two new Audubon reports provide some answers. Examining the distribution of 305 North American species since 1966, a national report, “Birds and Climate Change,” found that nearly 60 percent of species’ ranges have shifted north significantly, and that there is “an undeniable link” to climate change. “Our study shows climate change has affected the vast majority of birds in North America,” says Greg Butcher, Audubon’s director of bird conservation and report coauthor. A second study, from Audubon California, paints an equally bleak picture.

The national report used data from the Christmas Bird Count (CBC), a nationwide tally conducted by volunteers, which allowed researchers to map shifts in ranges during the past 40 years. Over that same period, average January temperatures have risen more than 4.5 degrees Fahrenheit in the continental United States. The report found that the purple finch has moved north 433 miles, and the red-breasted merganser, 317 miles—a trend repeated for many woodland and wetland species. As inland areas warm, these birds are moving away from the coasts. Birds migrate to escape cold winters, says Butcher. In mild winters, they stay put.

Climate is just one factor that affects bird movement. Food supply is another. People are planting ornamental fruit trees farther north, now that the trees can survive warmer winters. Feeders also keep birds such as the Carolina wren from leaving higher latitudes. Grassland species like meadowlarks, which have suffered in recent decades due to nationwide declines in the pastures and hay fields they prefer, are not wintering as far north because there simply isn’t available habitat, says Butcher. The lesson is chilling: Some birds can adapt to warming; others can’t.

“The power of [these studies] is just spectacular,” says Terry Root, a Stanford University ecologist and expert on climate change’s impact on birds, who wasn’t involved with the reports. “They looked for a pattern, and not only did they see one, they saw a big one, across the entire United States.”

Like the national report, Audubon California’s study used CBC data, but it also employed climate models to project how birds’ ranges might change as temperatures increase. Its prediction: Populations of one-quarter of the 312 California species studied will shrink significantly by this century’s end.

The report maps out future scenarios for each of California’s 48 Audubon WatchList species. For the threatened northern spotted owl, for instance, considerable tracts of the Sierra Nevada foothills might become uninhabitable, but its range could extend into northeastern California, where it’s now too cool for the bird. Other factors the models didn’t take into account, like nesting habitat and food availability, also determine a bird’s resilience in a new area. But basing the projections on climate change undoubtedly helps conservationists and land managers prepare, enabling them to determine crucial habitats to conserve as the planet heats up, says Gary Langham, Audubon California’s director of bird conservation and report coauthor. “Assuming nothing is going to change is the riskiest assumption of all.”

And as Carruth and Miller have seen, birds are already moving. “People tend to think climate change is something that will happen in the future,” says Butcher. “It’s happening now.” To learn how you can help birds, click here.

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