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Study says global warming shrinks birds

Scientists found that eight species had become between 2 to 4 percent smaller over the past century.

By Rod McGuirkAssociated Press Writer / August 21, 2009



CANBERRA, Australia

Some species of Australian birds are shrinking, and the trend will likely continue because of global warming, a scientist said Sunday.

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Janet Gardner, an Australian National University biologist, led a team of scientists who measured museum specimens to plot the decline in size of eight species of Australian birds over the past century.

The research, published last week in the British journal Proceedings of the Royal Society B: Biological Sciences, found that the birds in Australia's southeast had become between 2 percent to 4 percent smaller.

Over the same century, Australia's average daily temperature rose 1.3 degrees F. (0.7 degrees C), with the sharpest increase since the 1950s.

The research concluded that the birds were likely downsizing because smaller bodies shed heat faster than larger ones.

"It's the broad-scale, consistent pattern that we're seeing that makes us conclude that global warming is likely to be causing the changes," Dr. Gardner told The Associated Press.

She said she suspected that other Australian birds beyond the species studied were also shrinking and the trend will accelerate in the future as a result of global climate change.

"Simply because the predictions are that the warming is going to increase over the coming decades, so you might expect this (shrinking) response to increase as well," Gardner said.

Michael Kearney, a Melbourne University zoologist who is independent of the research, described its findings as both alarming and providing some hope for the future.

"This study strongly suggests that rising air temperatures in recent history have been stressful enough to prevent the larger individuals of a species from surviving and breeding," Kearney said.

"That we are seeing a potential evolutionary shift to smaller, and thus more heat-tolerant individuals is an alarming reminder of the consequences of global warming," he added. "But it also gives us some hope that evolutionary change will provide a temporary buffer in some cases."

Other studies have found similar trends of shrinking birds and mammals in Britain, Denmark, Israel, and New Zealand. Gardner's bird research is the first in Australia.

Birds and other animals around the world tend to be larger closer to the poles than those nearer to the equator. Scientists believe this phenomenon is an adaptation to heat stress. Gardner's team of researchers, from her university and the government's Commonwealth Scientific and Industrial Research Organization, have ruled out the Australian birds' changing insect diet over the past century as a cause for changing body size.

They found the growth rate of the birds' feathers remained unchanged. They would have expected feather growth to have slowed if poor nutrition had stunted the birds' growth.

The birds studied included four endangered species — jacky winter, brown treecreeper, gray-crowned babbler, and the hooded robin.

More common species studied were the speckled warbler, yellowrumped thornbill, white-browed scrubwren, and the variegated fairy-wren.