This young whooping crane is on its first fall migration, guided by an Operation Migration ultralight. Brown bars on its wings will fade by the time this bird migrates north in spring. / Joe Duff/copyright Operation Migration USA Inc.

As the warm summer months fade into the fall chill, birds will start their annual southward migration. Many species of birds will follow the exact migratory route they travel every year. This ability to recreate the route year after year has long puzzled researchers.

On Thursday, University of Maryland researchers said they’ve found a clue to this mystery. By studying the migratory patterns of whooping cranes who travel from Wisconsin to Florida each year, they’ve determined that young cranes follow the lead of an older crane. Their research will be published in the Aug. 30 issue of the journal Science.

One-year-old cranes traveling without an older companion veered an average of 60 miles from the usual flight path. When they had a guide, they stayed within 40 miles of the path.

Their ability to stay the course improves each year for the first five years of their lives. After age 5, they’re able to independently follow the route, and the still stays consistent from that point on. Groups that include a 7-year-old crane deviated 38 percent less than groups led by younger cranes.

Lead researcher Thomas Mueller, said the study is unique because most bird species do not live long enough to follow long-term learning processes.

“Here we could look over the course of the individual animals’ lifetimes, and show that learning takes place over many years,” he said in a press release. Whooping cranes live for 30 years or more in the wild.

“This is a globally unique data set in which we can control for genetics and test for the effect of experience,” said co-author William F. Fagan, a biology professor at UMD, “and it gives us an indication of just how important this kind of socially learned behavior is.

“Many biologists would have expected to find a strong effect of group size,” Fagan added, “with input from more birds’ brains leading to improved navigation, but we didn’t see that effect.”