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Climate Change May Shift Composition of U.S. Bird Species

Some species will prosper under global warming whereas others may see their habitats shrink further
gray vireo



flickr/Seabamirum

The gray vireo isn't a particularly beautiful bird.

Its wings are tinged brown, and its feathers tend to look scruffy. Pinyon jays, on the other hand, are gorgeous specimens. With jet-black beaks and bright blue plumage, these birds are a gem for bird watchers.

But beauty won't save the pinyon jay nor will blandness work against its cousin when climate change raises temperatures and alters bird habitats in the southwestern United States, according to research sponsored by the U.S. Geological Survey.

"We're assuming that the distribution of the species in the future will be constrained by the loss of their habitat," said James Hatten, a biogeographer at USGS and author of the research. "When we see large shrinkages, we also expect that there will be large losses in population."

Of the seven birds studied, the gray vireo is expected to flourish, its habitat increasing anywhere from 58 to 71 percent by the end of the century. The pinyon jay, however, isn't that lucky. Its habitat is already decreasing and will continue to do so, shrinking up to 31 percent in the same time frame.

Other birds such as the pygmy nuthatch and the Williamson's sapsucker are also forecast to lose habitat -- up to 81 percent and 78 percent, respectively. The black-throated sparrow will gain habitat, up to 47 percent more. The Virginia's warbler should stay relatively stable, losing about 1.5 to 7 percent of its preferred environment.

"It's a mixed bag," said Matthew Johnson, an ecologist with Northern Arizona University and author of the research. "Some species are going to do well, and some species are going to do poorly."

Pinyon jay: flight to nowhere
Johnson and his team used climate models to study the relationship between each target species and the vegetation it uses for food resources, which is affected by shifts in temperature and precipitation. Using bird distribution data spanning the breeding seasons between 1990 and 2009, scientists ran the numbers through six A1B climate models, which use middle-of-the-road predictions.

The team tallied the results with an agreement threshold, only accepting conclusions if at least five models predicted similar fluctuations.

The results weren't kind to the pinyon jay.

"Well, it looks like pinyon is dying," said Leland Pierce, a coordinator of terrestrial species recovery at the New Mexico Department of Fish and Game. "There's great concern that these animals are going out."

The pinyon jay relies on the nuts from pinyon trees for its main source of food. When pinyon nuts are plentiful, there is an increase in pinyon jay hatchlings, but when nourishment is scarce, hatchling populations scale way back, Pierce said. His department has already seen a reduction in pinyon pines, and according to the USGS study, which is still undergoing peer review, things are only going to get worse.

"You remove that habitat ... it faces extinction," Hatten said.

Of course, habitat reduction does not automatically mean a species will die. Even habitat growth cannot necessarily be correlated to a population increase.

Gray vireo, an inept opportunist
When overgrazing and wildfires in New Mexico destroyed native grasses, they opened up real estate that was quickly inhabited by juniper trees, the nesting grounds of gray vireos, Pierce said. The USGS research suggests that such an increase would result in a spike in gray vireos, but that hasn't been the case, according to Pierce.

"In theory, we should have zillions of these birds, and we don't," he said.

There is also the possibility that birds will adapt to shifting climate patterns and alterations to their habitat, switching nesting sites or sources of food.

"It's very hard to predict by species exactly how they'd respond," Pierce said. "Each species is going to be unique."

Despite such high levels of uncertainty, all three scientists agree that this vein of research is important. Birds are often used as an indicator of overall ecosystem health in Wyoming, Colorado and Arizona, Hatten said. Significant population changes could have significant, yet unknown, consequences.

In other cases, USGS research can be used to warn environmental stewards before a problem becomes irreversible.

"They see that those species are going to be at risk," Johnson said. "They can try to pre-manage for that.

"In some cases they won't be able to do anything," he added. "In other cases they can do some sort of restoration to save that species."

The severity of the impact on each species, whether comely or homely, will ultimately be up to us, Johnson said. If people can reduce emissions enough to change projected temperature increases, the USGS models could be inconsequential, he added.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500

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