When some birds open their wings, conspicuous white patches of plumage are revealed. Now new research has uncovered the reason for these ‘flashmarks’.
Michael Brooke of Cambridge University studied the habitat, feeding, migration and flocking behaviour of 210 species of waders - such as plovers, oystercatchers and lapwings - and compared these factors with the birds’ plumage. He found one important trend: birds that flock have the boldest flashmarks. But why?
The answer comes from established theories concerned with predator avoidance. One reason why we regularly see animals in groups is that there is safety in numbers - the ‘dilution effect’. Any one individual is a hundred times less likely to be killed if it stays close to ninety-nine others.
And birds have another trick - flight. But if one bird spots a predator and makes a dash for it, it will be an easy target unless the others in the group get the message and follow. The flashmark is thought to act as a signal for ‘take-off’ to the other flock members, explaining why it is most prominent in flocking species.
Once the flock is airborne, the marks may serve two more important functions: a signal to facilitate co-ordinated flight within the flock and a confusion tactic against predators. A dense and constantly changing mass of flapping and flashing makes it even harder for a predator to target any individual and allows the flockers to live to wade another day.
(Functional Ecology, vol 12, p339-46).