Why Migrating Birds Take Turns Leading the V-Shaped Flock

It turns out that flocks of migrating birds may rotate for the same reason that a cyclist team does. Scientists have found that these birds share the arduous task of leading a v-formation so that they can then take turns saving energy by following in another bird's wake.

The scientists studied 14 juvenile Northern bald ibis that were migrating from Salzburg in Austria to Orbetello in Italy. The birds were human-imprinted, which means that they followed a powered parachute carrying their handlers. Each of the birds wore tiny data loggers that allowed the researchers to examine how individuals within a flying v-formation interacted.

So what did they find? The experiment was designed to replicate the behavior of wild ibis where juveniles from the same location tend to migrate together. In this case, the researchers found the birds' behaviors mimicked that of wild flocks. Individual birds changed position frequently within the flock, flying in formations of two to 12 birds. Overall, individuals spend an average of 32 percent of their time benefiting from flying in the updraft produced by another bird's flapping wings and a proportional amount of time leading a formation.

"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 Bernhard Voelkl, the lead author of the new study, in a news release. "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."

The findings reveal how these birds participate in cooperative behavior. In this case, the researchers believe that the extreme risks involved in long migration journeys may have been the driver of this type of cooperative behavior in evolution.

The findings are published in the journal Proceedings of the National Academy of Sciences.

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