Climate change threatens more than half the bird species in the United States – with a significant fraction at risk of losing habitat with nowhere else to go, according to a new study.
Conservation efforts have made important strides in stemming or reversing the decline of a variety of birds across the United States, but the regional effects of global warming could seriously erode those gains, researchers say.
The study is one of two unveiled this week that also show the effectiveness the effectiveness of well-run conservation programs, as well as introduce a set of tools for crafting future projects in a changing climate. Each in its own way also identifies the fragmentation and destruction of habitat as the single largest threat to America's birds.
"The most immediate threats are habitat loss," says Ken Rosenberg, a researcher in the conservation science department of Cornell University's Lab of Ornithology in Ithaca, N.Y. "That's ongoing. Climate change might make it worse, but we can't let it take our eye off the ball of protecting habitat" now.
On Tuesday, a 23-member consortium of US and Canadian wildlife agencies, environmental groups, and universities, including Cornell, released its 2014 State of the Birds Report, a report card on the status of birds across ecosystems ranging from shorelines to deserts and forests.
The report card, the fifth issued since 2009, is based on surveys conducted largely by citizen scientists through projects such as the National Audubon Society's Christmas Bird Count and the US-Canadian-Mexican North American Breeding Bird Survey, as well as others.
Wetland birds are making a comeback in places where conservation efforts – under legislation such as the North American Wetlands Conservation Act, the Clean Water Act, and farm-bill conservation provisions – have been most intense, Dr. Rosenberg notes. The population of mallard ducks, for instance, is now 42 percent above its long-term average. Still, wetland losses continue to fuel declines in marsh species native to the US Southeast.
In America's grasslands, populations of many species have stabilized after years of losses, although Eastern meadowlarks and bobolinks continue to decline sharply as changing dairy practices and spreading suburbs have reduced available grasslands.
Hawaii remains a hotspot of concern, with 23 of its 33 native species on the Endangered Species List.
The consortium, formally known as the U.S. Committee of the North American Bird Conservation Initiative, has set up a watch list of about 230 species, out of 800 overall, that are the most vulnerable, Rosenberg says.
"We don't have data on a lot of these species in terms of long-term trends," he says. "But we do know what a lot of the threats are."
These species will be the focus of monitoring efforts.
Monitoring becomes especially important when projections of the regional effects of global warming are factored into the habitat equation, suggests Gary Langham, vice president and chief scientist of the National Audubon Society.
The Society released a report on Monday that used more than 30 years of data collected on birds, combined that with climate data from the period to establish the birds' preferred climate conditions, then used an ensemble of the latest climate models to how those conditions shift in location with climate warming.
The team producing the report looked at changes to climatic range in 2020, 2050, and 2080 under low, medium, and high emissions scenarios.
Out of 588 species studied, 274 are considered climate-stable, the report says.
But 314 species could lose more than half their current range in all three modeled scenarios. For 126 of the 314 species, the range loss comes with no compensating expansion elsewhere. They have nowhere else to go, so the team labeled them climate-endangered. For 188 of the 314 species, the birds could shift to new areas and so are merely climate-threatened.
In analyzing the results, Langham says he was struck by the large number of climate-endangered species and the unexpected habitats they occupy. Typically, mountain species have been seen as among the most vulnerable. They have nowhere to go but up, until there's no more up.
Instead, "the majority of those 126 species are lowland birds," he says. The fact that the range shrank, instead of shifted, "was very shocking and the fact that it was true for so many species was really disconcerting as well."
In addition, the effect of climate change "cut across all the categories we looked at," whether common, every day birds or those already on a threatened or endangered list.
The results have been submitted to the journal Conservation Biology for publication.
In the process, however, Langham and colleagues have set up what they hope will be powerful tools not only for conducting focused monitoring efforts, as the State of the Birds report does. The tools used to project the rise in unfavorable climate regimes also suggests the future locations for favorable regimes, which can inform habitat-conservation efforts.
Yet Langham cautions that climate alone doesn't ensure the success of birds that can shift with their preferred climate regime. They can migrate faster than the plants or animals on which they rely for food, and so might try to occupy a new range before it could support them.
In other cases, the newcomers might become invasive species in their own right.
For instance, the Mississippi kite is a raptor that breeds in colonies along the Gulf of Mexico. Its climate regime is projected to march north into the US heartland.
"If it is able to occupy that, it could expand its range dramatically, almost 2,000 percent" compared with today's range, Langham says. The bird feeds on small vertebrates – lizards, for instance, or other small birds. Will it satisfy its appetite at the expense of other species that are native to the heartland but struggling to exist?
Beyond their attempts to inform conservation decisions, the pair of studies have political value, says David Mizejewski, a naturalist with the National Wildlife Federation in Reston, Va.
Birding and an appreciation for these descendants of dinosaurs cut across political divides, he says. They are more immediate for more people than polar bears or penguins.
With the threat of species losses, either as direct fatalities or through shifts in ranges, looming with the destruction, fragmentation of shifts in habitat ranges, Dr. Mizejewski says, "Reports and studies like this are really important ... in trying to get people to focus on the issue of climate change and the impacts it's having."
[Editor's note: The original version identified Ken Rosenberg incorrectly.]