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Warming Forces Longer Migrations For Many Birds

April 15, 2009

A study released on Wednesday showed that climate change will force bone-weary birds migrating to Europe from Africa to log extra mileage, with possibly devastating consequences.

The research found that the annual voyage of some species, which fly north in search of food and suitable climes, could increase by as much as 250 miles.

Stephen Willis, a professor at Durham University in Britain and the main architect of the study, said marathon migrations for some birds are set to become even longer.

He said the added distance is a considerable threat to many birds, especially those like the Whitethroat, a common farmland bird.

Willis said in a statement: “As temperatures rise and habitats change, birds will face their biggest challenge since the Pleistocene era, which ended 11,000 years ago.”

The study, published in the Journal of Biogeography, noted that each year around 500 million birds migrate from Africa, some weighing as little as three-tenths of an ounce.

Birds have to fatten themselves up to twice their normal weight to complete a voyage that can be thousands of miles long. Some even shrink their internal organs to become more fuel efficient, making long distance travel easier on their bodies.

Co-author Rhys Green of Cambridge University said these tiny birds make amazing journeys, pushing themselves to the limits of endurance.

“Anything that makes those journeys longer … could mean the difference between life and death,” he added.

The researchers analyzed the current migration patterns of European Sylvia warblers, a group of birds common in Europe, and using simulation models, the scientists predict that breeding ranges will shift further northward over the 21st century, while wintering ranges will remain constant for most species.

The study found that 9 out of 17 species examined are projected to face longer migrations from 2071 to 2100, particularly birds that cross the Sahara desert.

During these long migrations, many birds traverse the Sahara and the Mediterranean Sea in one flight, while others make a pit-stop in northern Africa before crossing. Many fly at night, when temperatures are cooler.

The study said some species, like the Blackcap, have already begun to adapt by spending winters in Britain, but such behavior remains exceptional.

Nathalie Doswald, a Durham graduate student who worked on the study, said the projected distances for migration would require long- and short-distance fliers to increase their fuel loads by nine percent and five percent of lean body mass respectively.

The migration distance of the Orphean Warbler is forecast to jump from 1,700 miles to between 1,900 and 2100 miles, with even longer increases for the Subalpine and Barred Warblers.

However, migratory birds had proved adaptable before””surviving Ice Ages and the drying out of the once greener Sahara region about 6,000 years ago.

Willis said the study focused on warblers because of their widely differing strategies.

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