Birds fly the coop when climate shifts

UC BERKELEY (US)—Biologists studying birds in California’s Sierra Nevada mountains have found that 48 out of 53 species have adjusted to climate change over the last century by moving to sites with more favorable temperature and precipitation conditions.

“In order to conserve biodiversity in the face of future climate change, we need to know how a species actually responds to a warming climate,” says study lead author Morgan Tingley, a Ph.D. student at the University of California, Berkeley.

“Comparing past and present ranges of species that experienced climate change is one of the best ways to gain this knowledge. Understanding how species will respond to climate change allows us to take steps now to restore key habitats and create movement corridors that will help them respond to the changes we have coming.”

The study, conducted in collaboration with Audubon California, a non-profit state program of the National Audubon Society, includes data from a survey of 82 sites in the Sierra Nevada and details the changes in birds’ geographic range over the course of a century.

On average, those sites have seen a 1.4 degree Fahrenheit increase in temperature and nearly a quarter of an inch more rainfall during the breeding season since the early 1900s.

While individual species responded differently to environmental change—with some birds gravitating toward warmer temperatures and others preferring cooler climes—these idiosyncratic responses were successfully predicted for the majority of species by standard models that scientists employ to forecast the impact of climate change.

The researchers focused on abundant bird species whose range was restricted to the western United States. Based upon information from the species’ entire North American breeding range, the biologists determined the optimal average temperature and precipitation conditions in which the species breed, known as the “Grinnellian niche,” named after UC Berkeley ecologist Joseph Grinnell, who first developed the concept.

Researchers found a few species that did not relocate when the climate changed, but these species, including the Anna’s Hummingbird and Western Scrub-Jay, were generally better able to exploit human-altered habitats, such as urban or suburban areas.

The study builds upon surveys Grinnell conducted between 1911 and 1929.

Since then, global warming has emerged as another threat to Sierra Nevada habitats, presenting an additional impetus for scientists to resurvey those sites, which spanned as far north as Lassen Volcanic National Park, through Yosemite National Park, and south to Mount Whitney.

Craig Moritz, UC Berkeley professor of integrative biology and director of the Museum of Vertebrate Zoology, began the Grinnell Resurvey Project in 2003 with funding from the National Science Foundation, the Yosemite Foundation, and the National Park Service.

In many cases, the biologists were able to hike along the same trails that Grinnell and his colleagues walked some 90 years earlier. When comparing modern data with those earlier records, the researchers used statistical methods that minimized false absences of species when cataloging the occurrence of wildlife.

In 2008, the UC Berkeley-led team published the first study based upon the resurvey. The study reported that in response to global warming, small mammals were moving to higher elevations or reducing their ranges.

“When we did the mammal work in Yosemite, we saw some species moving up in elevation, but some did not, and we didn’t really know why,” says Moritz, who is a coauthor of the new study. “This new paper is giving us a clue about whether or not a species will be forced to shift when climate change alters its niche.”

Some bird species, such as the Dusky Flycatcher and the Green-tailed Towhee, were more sensitive to temperature changes, while precipitation was the motivating factor for the move of species such as the Yellow-rumped Warbler and the Lazuli Bunting. About a quarter of the species tracked were affected by both temperature and rainfall.

Modeling responses to future climate change typically assumes that species will move according to their preferred “Grinnellian” or “climatic” niche, but it has been unknown whether or not those assumptions were valid.

“This study shows the assumptions that underlie existing forecasts of how species will respond to climate change are valid, at least for most bird species in the mountains of California,” explains study coauthor and conservation biologist Steve Beissinger, UC Berkeley professor of environmental science, policy, and management.

“This is alarming because forecasts suggest many species will go extinct with the climate warming that we expect to occur, but it also gives us confidence that costly conservation investments made now based on climate forecasts will have a valuable payoff in the future.”

Tingley says that future studies should determine whether these findings are true for other species.

“Birds are arguably more mobile than many other species, so it remains to be seen whether other animals will be able to keep pace with future climate change, which is anticipated to be far greater in magnitude and faster in rate than what we have experienced thus far,” he says.

The findings were published the week of Sept. 14 in an online early edition of the journal Proceedings of the National Academy of Sciences.

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