Cited research: Proc. Natl Acad. Sci. USA doi:10.1073/pnas.1001763107 (2010)

Many bird species move cohesively in flocks, but what governs the behaviour of individuals and gives rise to this collective movement?

Ryan Lukeman of St. Francis Xavier University in Antigonish, Nova Scotia, Canada and his co-workers collected and analysed photographic data on the positions, movements and interactions of individual surf scoters (Melanitta perspicillata). These birds are found in flocks numbering into the hundreds on the coastal waters of North America.

The authors found that individuals position themselves, on average, 1.45 body lengths from their nearest neighbour, and move with a mean speed of two body lengths per second. They move in line with those in front of them and, if they get too close, will shift sideways. N.G.