For long flights, birds need to be energy efficient. To study this, biologists have been looking into one type of bird, the endangered northern bald ibis (Geronticus eremita). The study has found that the ibis frequently swaps out the leading bird in its migratory V formation, giving each leader a rest and evenly distributing the aerodynamic advantages of the flying arrangement among the flock.
With the research project, a team of scientists from the U.K., Germany, and Austria trained 14 captive birds to migrate from Austria to Italy. Each bird was fitted with high precision Global Positioning System (GPS) data loggers to record their relative position in the flock during the trip. The scientists found that the birds formed temporary pairs that took turns at the tip of the V, for over 60 percent of the total trip time. Each bird spent roughly the same amount of time leading as it did following. As a result of the constantly shifting flying formations, each bird spent only about a third of its flight time providing lift for other members of the flock.
The ibis group flight strategy appears to be a rare example of what the scientists are terming “reciprocal altruism.” The lead bird switched with the bird behind it sometimes as frequently as on the order of seconds, which might, the researchers speculate, aid in evenly distributing the positions of leader and follower. “The immediacy of reciprocation reduces opportunity for cheating,” study lead Bernhard Voelkl of the University of Oxford told New Scientist magazine.
Thirty percent of young ibises do not survive their first migration. However, as Voelkl told the BBC: “by reducing the amount of energy they use, they can really increase their chance of survival”.
Next, the science group wish to see if other birds are using similar strategies. The findings have been reported to the science journal PNAS. The paper is headed “Matching times of leading and following suggest cooperation through direct reciprocity during V-formation flight in ibis.”
