By the turn of the century, global warming will threaten the survival of more than half of all species of birds in the United States and Canada, a new report says.
Warming temperatures will dramatically alter the habitat ranges of birds in nearly every state, including Baltimore orioles and eagles in the Washington, D.C., region, forcing them to migrate to unfamiliar areas where they will have to adapt quickly or possibly perish, the study published by the National Audubon Society says.
Of the 588 species studied, 126 species will experience severe declines as soon as 2050, as half of their range, the sprawling areas they inhabit in summer and winter, becomes unsuitable because of increased dryness caused by warming.
An additional 188 species could greatly decline by 2080 if the pace of greenhouse gas emissions continues unabated. Over 90 per- cent of the world’s climate scientists agree that emissions from human activity are causing the planet to warm at an accelerated pace.
The report, released Monday by the society, a nonprofit group that advocates for birds, was commissioned by the U.S. Fish and Wildlife Service, which provided a portion of its funding.
“Since 1600, only about nine bird species have gone extinct in continental North America, but we’re looking at half of North American bird species at risk by the end of this century,” Gary Langham, the report’s lead author and the Audubon Society’s chief scientist, said in a statement.
The oriole, Maryland’s state bird and the mascot for Baltimore’s baseball team, might abandon the Mid-Atlantic region by 2050, the report said. The birds would likely follow cooler temperatures across the Northeast, Midwest and portions of Canada.
The wood thrush, the District’s official bird, might depart for similar reasons. The range of the bald eagle, the national symbol, could decrease by nearly 75 percent by 2080, and the common loon might not be able to breed in the lower 48 states by then.
As part of the same pattern, the study projects that the iconic brown pelican could leave Louisiana, the mountain bluebird might migrate out of Idaho, and the purple finch might move from New Hampshire.
Warming stands to harm vegetation that birds rely on for nesting and food, as well as insects and other prey, the study said.
“Every plant and animal is finely tuned to where it lives. When you change the fundamentals of that space, it throws it off, shifts things,” Langham said in a telephone interview before the report’s release.
“A grassland bird can’t go to the desert and an ocean bird can’t live in woodlands,” he said. “They are finely, finely tuned to the particular conditions where they thrive.”
When a species moves, it encounters others in its newfound habitat, setting off turf battles. “Competition is too fierce,” Langham said. “It’s likely that they won’t be able to successfully raise their young,” leading to far fewer birds.
But the report has a key blind spot. It cannot reliably say that many of the species it lists as threatened and endangered by climate change will not simply adapt in their current habitat, or thrive elsewhere.
John W. Fitzpatrick, executive director of the Cornell Lab of Ornithology, the nation’s premiere center for the study of bird conservation, called the report “a wake-up call.” But, he said, there are too many variables to definitively forecast a future for birds. “The uncertainty involved in this exercise is prodigious” because so many factors are involved.
“The word ‘tricky’ is an understatement,” he said. “I suspect that all the individuals involved in the modeling would admit this is taking a few variables alone and seeing what they say. This can’t be viewed as the end of the story.”
The report offers three scenarios on how birds might react to higher temperatures: Some might fly to a more suitable climate; others might stay and suffer as their habitats become unsuitable; and some might simply adapt.
“The models don’t describe how heat affects them. . . . It looks at the space they live in,” Langham said. He added that “there absolutely is a chance that some birds will be able to adapt,” and repeated what scientists have long known: Plants and animals do adapt to climate change.
However, that usually “happens over 10,000 to 15,000 generations historically,” he said. “This will unfold over the lifetime of a 5-year-old.”
The report took over seven years to complete. Researchers compiled four decades of data — detailing where birds congregate in summer and winter — from the U.S. Geological Survey and the Audubon Society’s yearly Christmas Bird Count. They used historical climate data to measure seasonal temperatures and monthly precipitation averages where the birds roost.
The report also used a computer algorithm known for its ability to detect the complex relationship between animals and seasons within a habitat. Species were placed in climate sensitivity categories based on how their habitats’ climates were projected to change.
“It was really important to let the birds tell us how it would affect them based on where they are now,” Langham said. “For eagles, there is a combination of wet periods, dry periods and precipitation that could affect them.”