Date: June 9, 2016
Source: University of Exeter
Nesting birds time their escape from an approaching predator depending on how well camouflaged their eggs and their own bodies are, researchers from the University of Exeter and the University of Cambridge have discovered.
This is the first study to show that the camouflage of an animal or that of its offspring can explain the variation in risk-taking behaviour when approached by a predator.
Researchers worked with a team of skilled local assistants in Zambia to find the nests of several species of ground-nesting birds. Once a nest was found they monitored its progress, recording the escape distance of the adult bird each time they approached and, using camera traps, identified key predators such as banded mongooses, vervet monkeys and grey-headed bush shrikes -- and even human children.
In complex environments it is hard for animals to perfectly match their background. When an animal's camouflage is poor it has a higher risk of being detected and eaten by a predator, so it should more readily flee from an approaching threat. The researchers therefore set out to test whether the distances at which birds fled from their nests on the exposed ground was related to the camouflage of their plumage and eggs.
They found that birds that usually flee from predators at long range, such as plovers and coursers, stayed on their nest for longer when the pattern of their eggs was a better match to the background. They also adjusted their behaviour in the heat of the middle of the day, letting a predator approach a little closer before fleeing. This probably allows them to shade their eggs for as long as possible, and so reduce the chance of them cooking in the African sun. By contrast, another group of birds, the nightjars, usually sit tight as predators approach so that their eggs are concealed by their camouflaged bodies until the last minute. Sure enough, nightjars stayed on their nests longer when the colour and pattern of their own plumage, rather than that of their eggs, was a better match to the background.