Migrations are inherently risky for birds. Previous studies have suggested that up to 35 percent of juvenile birds can die of exhaustion on their first migration.
Flying in V-shaped or echelon formation can help to save vital energy: it is estimated geese can make energy savings of 10-14 percent by gaining lift from flying in the updraft of other birds.
To understand how birds interact in flight, Dr Voelkl and his colleagues studied 14 juvenile Northern bald ibises migrating from Austria to Italy.
They investigated why supposedly selfish individuals would altruistically use up more of their energy leading a formation and how flocks guard against free-loaders benefiting from traveling in the wake of other birds without ever leading themselves.
The scientists found that individual birds changed position frequently within the flock, flying in formations of 2 to 12 birds.
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.
“Our study shows that the ‘building blocks’ of reciprocal cooperative behavior can be very simple: ibises often travel in pairs, with one bird leading and a ‘wingman’ benefiting by following in the leader’s updraft,” said Dr Voelkl, who is the first author of a paper published in the Proceedings of the National Academy of Sciences.
“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 by traveling in a pair the energy costs for both individuals are reduced, whilst larger formations bring even greater energy savings.
“We found that larger formations of ibises were still made up of these turn-taking pairs,” Dr Voelkl said.
“The checking that went on within these pairs was sufficient on its own to prevent any freeloaders hitching a free ride within a v-formation without leading. In fact, surprisingly, we found no evidence of cheating of any kind within these flocks with the level of cooperation, with individuals benefiting from following 32 percent of the time, significantly higher than expected.”
Bernhard Voelkl et al. Matching times of leading and following suggest cooperation through direct reciprocity during V-formation flight in ibis. PNAS, published online February 2, 2015; doi: 10.1073/pnas.1413589112
This article was first published by Sci-News on 03 Feb 2015. Lead Image: Northern bald ibises (Geronticus eremita) take turns saving energy by following in another bird’s wake. Image credit: M Unsöld.