Social networking teaches birds to fend off cuckoos

Scientists have discovered that birds have more than just evolution to thank for their ability to ward off unwanted approaches from cuckoos - they also have the avian equivalent of neigbourhood watch to show them how to defend themselves!

Writing in this week's Science, Cambridge University zoologists Nick Davies and Justin Welbergen explain how they set up fake cuckoos next to the nests of reed warblers in the Cambridgeshire Fenland. They found that younger birds tended to be frightened off by the cuckoos, which have evolved to resemble hawks, but older birds were more audacious and would noisily mob the models.

The research duo thought that the younger birds might be learning to recognise and react to the cuckoo by watching the reactions of their more experienced neighbours. To test this hypothesis they set up the experiment a second time and also played sounds made by reed warblers mobbing cuckoos to attract neighbouring animals, which perched nearby watching how the birds warded off the cuckoo threat. After a short period they then subjected birds in neighbouring nests to the cuckoo treatment.

These animals, which had previously been spectators, reacted far more vigorously to the cuckoo this time, suggesting that they had taken a leaf out of their neighbour's nest and learned to recognise a threat and how to respond to it! "This explains," says Nick Davies, "why there are examples of birds becoming less susceptible to cuckoo parasitism much more quickly than evolution alone would allow. It's achieved through social learning like this."