The Heat Is Online

Warming Drives Birds North


May 21, 1999

LONDON - (Reuters) British birds are spreading their wings and extending their range northwards to beat global warming, scientists said.

In the past 20 years many birds have pushed their northern boundaries by an average of 19 km (12 miles) but their southern limits have remained the same, they said.

"This general northward shift took place during a period of climatic warming, which we propose might be casually involved," Chris Thomas and Jack Lennon said in a letter to the science journal Nature.

The researchers used breeding atlases to map the northern migration of 101 bird species.

"If similar changes take place in response to the much larger climate warming that is predicted for the next 50-100 years, we could expect to see much more serious shifts in species distribution," Thomas added.

In a separate report in Nature, scientists from the University of Tennessee in Knoxville, predicted that continental birds with a breeding range of less than 100,000 sq km (38,610 sq miles) would become more vulnerable to extinction.

Since 1600, 97 of the 108 species that have become extinct have been on islands but 452 of the total 1,111 species that are considered to be threatened are continental, said scientist Lisa Manne.

"Historically it has been the case that more extinctions have been on islands and that was the striking part of our findings. History leads us to believe one thing but what we're really finding is something different," said Manne.

(C) Reuters Limited 1999.

Climate warming could be pushing birds farther north to breed, a new study suggests

By Marina Chicurel, Discovery

Ecologists Chris D. Thomas and Jack J. Lennon of the University of Leeds in England analyzed the distributions of nesting birds in Britain over 20 years, roughly between 1970 and 1990. The northern boundaries of the ranges of many species appear to have moved northward, on average by 11.7 miles, the scientists report in this week's journal Nature. Previous studies have suggested that changes in climate are spurring many organisms -- including butterflies, birds, amphibians, and plants -- to head to cooler regions either by moving northward, or climbing mountains.

But many of these studies were unable to prove that the shifts were caused by true migrations rather than by changes in total area occupied, as occurs when populations grow or shrink.

Using data from two atlases of breeding birds in Great Britain, Thomas and Lennon measured changes in the boundaries of breeding areas of more than 100 bird species and compared them to changes in breeding ground area.

"This sort of creativity in analyzing what little data we have is extremely important," says ecologist Camille Parmesan of the University of Texas in Austin.

Thomas and Lennon estimate that, on average, the northern edges of species that breed in southern Britain have moved almost 12.4 miles north in 20 years. Surprisingly, they did not observe a corresponding shift in the southern borders of northerly species. For now, nobody is exactly sure why.

The researchers blame climate warming for the northward shift because the shift coincided with a period of warming, because other studies indicate that changes in temperature affect bird reproduction, and because the distribution of bird species in Britain is correlated with temperature.

"I'm surprised the (northward) changes were so slight," says ornithologist Jeff Price of the American Bird Conservancy in Colorado, who is conducting similar studies in North America.

"On its own, it isn't really strong evidence for climate warming shift," Price says." He says he's measured a 45.3-mile northward shift in a warbler population over 24 years, for example.

"It's when you put all the studies together that you start building a picture of what's happening," says Parmesan. "And that picture is increasingly saying that very small changes in climate make quite large changes in natural systems."