Study Shows Breeding Ranges of North American Birds have Shifted Due to Climate Change

A new study led by an Auburn University researcher shows that the breeding ranges of North American birds have shifted northward coinciding with a period of increasing global temperatures.

Alan Hitch, a doctoral student with AU’s School of Forestry and Wildlife Sciences, along with his master’s degree advisor, Paul Leberg, studied the breeding ranges of 56 bird species using data collected by the North American Breeding Bird Survey, a long-term, large-scale, international avian monitoring program initiated in 1966 to track the status and trends of North American bird populations.

“Our results add to an increasing body of scientific research documenting the effects of global climate change,” Hitch said. “It also raises questions about whether northward shifting ranges could be detrimental to some species.”

Hitch and Leberg concentrated their study, which was published in the April issue of Conservation Biology, on arboreal and semiarboreal birds – types of birds that primarily live in backyards or forests and eat seeds or insects – living east of the Rocky Mountains such as the Common Ground-dove, Bachman’s Sparrow, Northern Mockingbird, Bewick’s Wren and the Golden-winged Warbler among others. The analysis was designed to help account for factors other than climate that might explain the range shift, including population expansions and land-use changes.

“To demonstrate a causal link between climate change and shifting ranges is difficult,” he said. Hitch and Leberg chose to study a variety of species on a large geographic scale to determine if there was a causal link between climate change and shifting breeding ranges. “If breeding ranges were moving because of climate change, then the effect should be seen among multiple species over large scales,” he said.

Hitch looked at the breeding ranges throughout a 26-year period. If the ranges were expanding northward and southward, Hitch said then the data would suggest that the birds were simply expanding their ranges. However, Hitch found that the birds’ ranges were only expanding northward leading to the conclusion that climate change might be responsible for the shift in range.

According to Hitch, identifying the forces behind the shifts is the first step to understanding whether these shifts may lead to the extinctions of local populations. “It was important to determine whether climate change was the likely cause of the range shift,” he said. “The fact that the northward shift in North America was similar to that seen in an earlier study conducted in Great Britain, gives us some support for that conclusion.”

“It is difficult to predict when or if the forces behind the distributional shifts of birds we report here may lead to extinctions of local populations,” Hitch said. “Birds are extremely mobile which allows them to move in response to climate change; however, prey or habitats that birds rely on for survival may not be able to adapt so easily.”

Hitch conducted the research for the study while he was a master’s degree student at the University Louisiana Lafayette. He is currently a doctoral student in the AU School of Forestry and Wildlife Sciences researching avian habitat relationships.

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