Flying in a V-formation is toughest for the leader, and migrating birds compensate by taking turns so that no one gets exhausted, international researchers said Monday.
The authors of the study in the Proceedings of the National Academy of Sciences, a US peer-reviewed journal, described the discovery as the "first convincing evidence for 'turn taking' reciprocal cooperative behavior in birds."
The research is based on 14 northern bald ibis (Geronticus eremita), that migrate from Salzburg, Austria to Orbetello, Italy.
Each bird wore a data-logging device that allowed scientists to track how individuals acted within the flying V-formation.
Researchers found that the "birds changed position frequently within the flock."
"Overall, individuals spent an average of 32 percent of their time benefiting by flying in the updraft produced by another bird's flapping wings and a proportional amount of time leading a formation," the study said.
Scientists believe this high level of cooperation evolved as a survival necessity.
Since migration is risky -- some research has found that more than one third of young birds die of exhaustion on their first trip -- those that learn to fly in formation and change positions regularly can save energy, getting a bit of a free ride from flying in the updraft of other birds.
"Our study shows that the building blocks of reciprocal cooperative behavior can be very simple: ibis often travel in pairs, with one bird leading and a 'wingman' benefiting by following in the leader's updraft," said lead author Bernhard Voelkl of Oxford University's Department of Zoology.
"We found that in these pairs individuals take turns, precisely matching the amount of time they spend in the energy-sapping lead position and the energy-saving following position."
Even when in a larger group, the pair philosophy reigned, and freeloaders -- those who might be happy to glide in the back and never take a turn in the front -- were nowhere to be found.
"In fact, surprisingly, we found no evidence of cheating of any kind within these flocks," he added.