Avian evidence

Global warming driving birds northward

By SANDY LONG

UPPER DELAWARE REGION — Forty years of dedicated citizen involvement in the form of counting birds across the United States has added up to a revealing and disturbing trend pointing to the impact of global warming on the nation’s 305 bird species.

After analyzing data gathered during the Audubon Society’s annual Christmas Bird Count (CBC), Audubon scientists have discovered that 58 percent of those species that winter on the continent shifted significantly northward, some by hundreds of miles.

Barbara Leo, who coordinates the CBC in the Upper Delaware region, said the count reflects early winter movement of migrant and resident birds. “There was a noticeable increase in bluebirds this year,” said Leo, who speculated that the increase may also be influenced by a dedicated effort to increase the number of bluebird nesting boxes throughout the region.

Among the population shifts observed in Pennsylvania is the American robin, which has increased by 659 percent during the winter months and has moved north more than 200 miles. American black duck populations have moved 182 miles north, dramatically decreasing their population in Pennsylvania. The Carolina wren and Eastern towhee have greatly extended their range northward and have expanded their populations throughout the state.

In New York, Eastern bluebirds have substantially increased, moving 114.5 miles northward over the last 40 years. Northward movement has also been demonstrated by the Carolina wren, red-bellied woodpecker, snow goose and turkey vulture.

All species showed some degree of movement, with 70 percent of forest and feeder birds trending northward, but only 38 percent of grassland species doing so. Depleted habitats may be preventing the shift for these species, which face the combined threats of climate change and habitat loss.

While acknowledging that population shifts are not uncommon, the movement by such high percentages of multiple species is believed to suggest an undeniable link to climate change.

The failure of some species to move at all may portend even greater problems. Likely due to the unavailability of grassland habitat, species such as Eastern meadowlark, vesper sparrow and burrowing owl, were unable to move to areas of more moderate northern temperatures.

Conversion of such habitat for human uses like energy production, agriculture and development, in combination with global warming, is expected to result in continued population declines.

Widespread ecological disruption may become the norm without substantial changes. “Birds are showing us how the heavy hand of humanity is tipping the balance of nature and causing ecological disruption in ways we are just beginning to predict and comprehend,” said report co-author and Audubon Director of Bird Conservation, Greg Butcher, Ph.D.

“Common sense dictates that we act now to curb the causes and impacts of global warming to the extent we can, and shape our policies to better cope with the disruptions we cannot avoid.”

Wes Hochachka, assistant director of the bird population studies program at the Cornell Lab of Ornithology in Ithaca, NY, affirmed the Audubon findings.

“The study is perfectly consistent with what we’ve seen over the past decade in Europe and America,” Hochachka said.

Calling the findings “a harbinger of things to come,” Hochachka noted that ultimate outcomes could vary quite a bit, due to the effects of such climatic changes as episodic or irregular rainfall events, increasingly wider swings in temperature variation and the impact of such events on the vegetation needed by particular bird species.

“Experts predict that global warming will mean dire consequences, even extinction, for many bird species, and this analysis suggests that the process leading down that path is already well underway,” said Audubon President John Flicker. “We’re witnessing an uncontrolled experiment on the birds and the world we share with them.

“The birds are giving us yet another warning that it’s time for urgent action,” added Flicker. “People hear about melting glaciers and changing weather, but now they can witness the impact global warming is having with the birds they see or don’t see right outside their doors. These birds are our ‘canaries in the coal mine’ and they’re telling us that we’d better do something fast to curb global warming and to protect habitat.”

To learn what you can do, visit www.Audubon.org where a national petition demanding aggressive federal policy action can be accessed, along with other steps to take.

The Audubon Society is currently tabulating the results of its Great Backyard Bird Count, which is actively updated at www.Birdcount.org and reflects bird species being observed across the nation during a four-day period in February.