Older Cranes Keep Younger Birds on Track During Seasonal Migration: A Study

When it comes to learning migratory routes, nurture appears to play as big a role -- if not bigger -- than nature for the whooping crane, a new study shows.

Researchers found that, when left to their own devices, 1-year-old birds veered an average of 60 miles from the course. This decreased to less than 40 miles in the presence of older birds. Meanwhile, groups that included a seven-year-old adult deviated an average of 38 percent less from a migratory straight-line path than those without.

All told, the study suggested that individual cranes' ability to stick to a route increased every year until about the age of 5, at which point it remained roughly constant.

Published in the journal Science, the study is based on data taken from an intensive effort designed to restore the endangered bird to its native range after numbers dropped to just 25 in the 1940s.

Since 2001, the Whooping Crane Eastern Partnership has worked to establish a group of cranes in the Eastern United States, each summer training a group of captive-raised chicks to follow an ultralight aircraft on a 1,300-mile journey to their Florida wintering grounds. After this first human-assisted migration, however, the young birds are left to make the journey on their own, usually with the help of other whooping cranes, while researchers track them via satellite transmitters, radio telemetry and on-the-ground observations.

Based on data collected between 2002 to 2009, the researchers found that genetic relatedness, gender and the size of the group had little effect on the cranes' ability to stay the course.

"Many biologists would have expected to find a strong effect of group size, with input from more birds' brains leading to improved navigation, but we didn't see that effect," co-author William Fagan, a biology professor at the University of Maryland, said in a statement.

Ultimately, only one experienced bird was needed to keep an entire group on track, leading the researchers to hypothesize that older birds are better at recognizing landmarks and coping with inclimate weather.