Knocking birds

Students on a Florida campus who strayed too close to a mockingbird nest found themselves under personal attack, according to a new study. A species of songbird has been shown to identify individual people in a crowd in order to target them aggressively if they pose a threat to their nests. In the new study, by Douglas Levey and colleagues at the University of Florida, Gainsville, in the Proceedings of the National Academy of Sciences (published online), North American mockingbirds distinguish between individual men and women out of many thousands based on whether they have a history of getting too near to their nests. It is the first time anyone has shown that wild birds are able to tell people apart and is one of the rare examples of one species being able to distinguish between individual members of another species, the researchers said. The mockingbirds in the study quickly learnt to identify people who regularly came too close to their nests on a busy university campus populated by thousands of passing students. The birds responded to further encroachments by screeching, dive bombing and sometimes grazing the heads of the intruders. However, this extreme aggression was limited to those people who had already come too close to the birds’ nests on two previous occasions. First-time human intruders were treated with far less aggression, the researchers found. “Previous studies of interspecific recognition of different individuals are anecdotal and/or restricted to laboratory settings that lack ecological relevance,” the authors write. “Likewise, honey bees can learn to forage preferentially under photographs of particular human faces that are associated with rewards, demonstrating the ability of bees to distinguish between two-dimensional, stationary images of faces, but not resolving whether they can learn to distinguish between actual humans.” “The primary strengths of our study are that it was done on wild birds and used an experimental approach to measure a behaviour directly linked to fitness,” they believe. “Assuming that mockingbirds’ ability to quickly recognise individual humans in a complex and novel environment somehow reflects cognition, it is surprising to find such an ability in a small passerine; it would more likely predicted in parrots and corvids because of their ‘cognitive superiority’ over other birds.”