Migrating Birds Affected By Global Warming: Newer Generations Are Nesting and Hatching Earlier

By Gabrielle Jonas on November 13, 2013 10:27 AM EST

Bar-tailed Godwit in breeding plummage
This wading bird is changing its migratory patterns in response to global warming and other environmental stressors. (Photo: Andreas Trepte, www.photo-natu)

Birds who migrate over short distances are nesting and hatching earlier, most likely in a response to global warming, a new study suggests.

Ornithologists have long suspected that individual migrating birds are arriving earlier at their winter breeding and nesting destinations in response to global warming. But that's not the case, the authors of the new study contend. Individual short-term migrating birds are still arriving at their breeding and nesting sites like clockwork, they noted. But, their youngsters are leaving earlier on their spring migration. And parents are equipping them to do this by nesting earlier after they arrive at their winter destinations, according to a study published Wednesday in the ornithology journal, Proceedings of the Royal Society B.

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Helping the ornithologists arrive at this conclusion were more than two-thousand birdwatchers who reported sightings of colour-ringed black-tailed godwits over a 20-year period along the birds' entire flyway, which reaches from Iceland to Spain and Portugal. The godwit is  a large, striking bird and easy to spot: It's a wader or shorebird with a long straight bill, a white bar on its wings, and a large dark bar on the tip of its tail feathers. It breeds in meadows, marshes and bogs, where it forages for worms, insects and mollusks. In Asia, godwits are often foraging for rice seeds in cultivated rice fields.

During the 20-year observation period, a flock of Icelandic black-tailed godwits advanced its spring arrival date in Spain and Portugal by two weeks. Godwits hatched in the late 1990's arrived in May, but those hatched in the late 2000's arrived in April. "The arrival dates are advancing because the new youngsters are migrating earlier," said the study's lead author, Dr. Jennifer A Gill from the University of East Anglia's school of Biological Sciences.

Global warming is a factor in the altered migration pattern because godwits tend to nest earlier in warmer years. Birds that hatch earlier have extra time to put on the extra ounces of body fat for migration, Dr. Gill said.  "It's a particularly important question because the species which are not migrating earlier are declining in numbers," she said.

Black-tailed godwits was listed as "Near threatened" on the 2006 red-list compiled by The World Conservation Union. In addition to global warming, agricultural intensification and wetland drainage of breeding grounds are considered culprits in their declining numbers.

"This study is important because it provides a glimpse into the mechanism behind the advances in arrival dates that we've observed over the past decades," Dr. Chris McClure of the Department of Biological Sciences, Boise State University told International Science Times.

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