Early environment may be key to determining bird migratio...( How young migratory birds choose the...)

How young migratory birds choose the nesting location of their first breeding season has been something of a mystery in the bird world. But a new University of Maryland/National Zoo study of the American redstart suggests that the environmental conditions the birds face in their first year may help determine where they breed for the rest of their lives, a factor that could significantly affect the population as climate change makes their winter habitats hotter and drier.

We found that where the birds go in their first winter, a process called natal dispersal, may determine the area, within several hundred miles, where they will breed over their lifetime, said Colin Studds, the University of Maryland PhD student who led [C1]the study. An important factor appears to be the availability of water in their winter habitat.

The study appears in the February 18 issue of the Proceedings of the National Academy of Sciences. Co-authors of the paper are Peter Marra, of the Smithsonian Migratory Bird Center, and Kurt Kyser, of Queens University, Ontario.

The Rich Get Richer

The American redstart is a warbler that migrates between breeding grounds in North America and winter spots in the Caribbean and South America. The team studied redstarts that winter over in Jamaica in two very different habitats that are right next to each other.

One is a very lush mangrove with water and lots of insects for the birds to eat, Studds said. Right beside it is a fairly harsh dry habitat, with very little water and not as good a food supply.

By studying the tail feathers of young redstarts between their first and subsequent summer nestings, the researchers found that the difference between wintering over in the lush mangrove or in the drier real estate next door may help set off a lifelong cycle of habitat location.

The mangrove birds leave earlier to breed, dont migrate as far north, and return to the water and food-ric
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