Here’s a lesson on road trips from whooping cranes: For efficient migration, what matters is the age of the oldest crane in the group. These more experienced fliers nudge youngsters away from going off course on long flights.
“The older birds get, the closer they stick to the straight line,” says ecologist Thomas Mueller of the University of Maryland in College Park, who crunched data from 73 Grus americana migrating between Wisconsin and Florida.
One-year-olds traveling with other birds of the same age, the analysis says, tend to deviate about 76 kilometers from a direct route. But if they fly in a group with an 8-year-old crane, they stray 38 percent less, or about 47 kilometers, Mueller and his colleagues report in the August 30 Science.
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Eight years of data on these endangered cranes summering in Wisconsin’s Necedah National Wildlife Refuge offered a rare chance to parse how birds find their way. Conservationists have been rebuilding this eastern migratory population of the once widespread birds. Researchers release captive-bred cranes in Wisconsin and lead each class of newbies, just once, with an ultralight aircraft to Florida’s Chassahowitzka National Wildlife Refuge for the winter. Cranes navigate back to Wisconsin on their own.
Age and presumably experience mattered more than genetics for efficient migration, Mueller says. Each bird’s pedigree is known, and closely related birds didn’t navigate in noticeably similar ways.
Whether this is a true case of social learning, with young birds picking up migration savvy from flying with older ones, is a question that intrigues behavioral biologist Dora Biro of the University of Oxford in England. Youngsters might not be learning from their flight mates so much as benefiting short-term from the older birds’ expertise. The difference is not just semantics, she says, but is important for understanding how generations might be transmitting information about migration.
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For his part, Mueller suspects that the younger birds do learn from the older ones, he says, which poses a concern for those trying to re-create crane populations with captive-bred birds. “They may have a culture that has been lost,” he says. “To rebuild it — that won’t happen overnight.”