Alaska's tiny Middleton Island was the subject of a feature story by biologist and nature photographer Brian Guzzetti in our December 2008 issue. It described how the powerful 1964 Alaska earthquake dramatically altered the island's birdlife: It raised the shipwrecked USS Coldbrook from its watery grave and created a vast intertidal zone that attracts migrating shorebirds and is now home to the world's largest known breeding population (700 pairs) of Black Oystercatchers. (Subscribers can read it here.)
Today, we've learned about a fascinating new study of another Middleton resident: the Black-legged Kittiwake. The bird is the world's most abundant gull, numbering approximately 6-7 million pairs. Most breed in huge colonies in the North Atlantic from Canada and Greenland to Great Britain, Iceland, and Norway. Smaller numbers occur in western Canada, Alaska, Russia, and Japan. The population on Middleton Island, according to Guzzetti's article, has fallen from about 160,000 in 1978 to 14,000.
Researchers have been studying the decline for many years, and recently they wanted to know if genetics played a role in the kittiwake's mating patterns. The scientists knew that kittiwakes are monogamous, that divorce is rare, and that both parents contribute to chick rearing.
What they found after analyzing the breeding success and DNA of 348 adults that nested on the ledges of an abandoned U.S. Air Force radar tower is something that can be said about only a few other animals: Black-legged Kittiwakes somehow know how to avoid inbreeding.
All of the other animals known to avoid inbreeding — Ruffs, Kentish Plovers, Western and Common Sandpipers, mice, sand lizards, and humans — are polygamous. The finding that kittiwakes avoid inbreeding is the first for a monogamous species.
"We found that kittiwake breeders were not paired randomly, but with mates that were less genetically similar than expected by chance," the researchers write in a paper published today by the open-access journal BMC Evolutionary Biology. The few closely related pairs in the study produced eggs that were less likely to hatch and chicks that were more likely to die. According to lead author Hervé Mulard of the Ecology Institute in Paris, "inbreeding is devastating in this population."
The natural follow-up question, of course, is: How can kittiwakes tell who their relatives are in a large anonymous population?
The research team, which consists of scientists from Austria, France, Switzerland, and the U.S. Geological Survey's Alaska Science Center, hopes to answer that question by studying whether, similar to humans, birds might be able to detect a mate's genetic profile from their body odor. "This ability could serve strictly monogamous species well," says Mulard, "as they may experience the highest selective pressure to choose genetically distant mates." --M.M.
Photo: A Black-legged Kittiwake perches over its chick on the rim of its nest. (Brian Anderson/U.S. Fish and Wildlife Service)