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Old birds help teach younger birds to migrate

Whooping crane in flight.
[Image © Operation Migration USA Inc.; Photographer: Joe Duff]

Many birds migrate thousands of miles each year to reach their breeding grounds. But how do they know where to go? For years, scientists have wondered how much of a bird's migration route is learned from experience—and how much is passed on genetically. Now, researchers studying North American whooping cranes find that old birds help younger to stay on track and keep flying in a straight line to their destinations. So, social learning among whooping cranes is important, they say.

An intensive conservation effort to save North American whooping cranes from extinction gave Thomas Mueller and his colleagues a chance to analyze 8 years of data on the birds. The researchers studied a group of cranes from Necedah National Wildlife Refuge in the U.S. state of Wisconsin that were bred completely in captivity. During the birds' first fall at the refuge, the cranes were guided by an ultra-light aircraft with a human pilot all the way to their breeding grounds in Florida. After that first migration, however, the cranes flew freely in groups without any aircraft to guide them.

The researchers discovered that the presence of older, experienced birds in a migratory group helped the group fly in a straight line to their destination. When the oldest cranes in the group were just 1 year old, the birds veered off-course by about 47.3 miles, but when the oldest cranes in the group were 8 years old, the birds only went off-course by about 29.1 miles, they say.

Their findings don't reveal anything about the potential genetic aspect of migrating—or the information that's passed on through their genes—but they do show that whooping cranes learn their migration routes over many years, with older birds helping younger birds to find the way. The results may be important for future conservation efforts, since migratory performance is often linked to breeding success.