Birds move in response to climate change


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Ecologist Joseph Grinnell could not have known that in 1911, or even in 1929, but the work he did in those years has provided a baseline for studies today.

Grinnell and his team methodically catalogued birds, reptiles and amphibians on hikes through California's Sierra Nevada. Generations later, new teams have visited the same locations, and documented changes.

Monday, in the journal Proceedings of the National Academy of Sciences, they made headlines.

Recent studies confirm that birds move in response to changes in climate. Of 53 species, 48 in the Sierra Nevada Mountains have adjusted to climate change over the last century by moving to sites with the temperature and precipitation conditions they favored.

The few species that did not move, 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 researchers said.

The study, conducted in collaboration with Audubon California, includes data from 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 temperature increases of 1.4 degrees Fahrenheit and about a quarter of an inch more rainfall since the early 1900s.

While individual species responded differently to environmental change -- some birds gravitated towards warmer temperatures while others preferred 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. These conditions are known as the "Grinnellian niche," named after Grinnell, who first developed the concept.

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.

Modeling responses to future climate change typically assumes that species will move according to their preferred "Grinnellian" or "climatic" niche, but few studies have directly examined whether 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," said study co-author and conservation biologist Steve Beissinger. Beissinger is a 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."

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