In the first published account of wild animals recognising individuals of another species, the songbirds attacked people who had threatened them in the past

Mockingbirds can remember people who have threatened them and even start dive-bombing them if they see the person again, a study has found.

An urban population of the songbirds ignored most passers-by, but took to the air when they recognised people who had approached their nest days before.

When the birds spotted a previous offender, they started screeching and set off to harass the person with swooping dives, at times grazing the tops of their heads.

The extraordinary behaviour, reported in the US journal Proceedings of the National Academy of Sciences, is thought to be the first published account of wild animals in their natural setting recognising individuals of another species.

Photograph: Lou Guilette/PNAS

"We tend to view all mockingbirds as equal, but the feeling is not mutual. Mockingbirds certainly do not view all humans as equal," said Doug levy, a professor of biology at the University of Florida in Gainesville, who led the study.

The findings offer clues to why some animals are able to thrive in large cities and suburbs while others fare less well.

"The real puzzle in the field of urban ecology is to figure out why certain species thrive around humans," Levy said. One idea is that the more successful creatures have an inborn ability that allows them to adapt better to the environment than other animals.

Mockingbirds are one of the most common birds nesting in the trees and shrubs on and around the university's campus in Gainesville.

In the study, which took place last spring and summer during the birds' nesting season, volunteers walked up to the mockingbirds' nests and gently reached out to touch the nest edges. The same individuals repeated the act for three more days. On the fifth day, different volunteers approached the nests.

By the end of the study, 10 volunteers had visited 24 birds' nests. Each time, the person wore different clothes and walked a different route to the nest.

Video recordings of the birds' reactions showed a dramatic change in the birds' behaviour when they recognised someone who had recently approached the nest.

Within two days, the birds began reacting much more quickly to people they recognised. They started producing alarm calls earlier and left their nests to fend off the intruders with aggressive flying displays.

The airborne attacks seemed to be targeted at individuals the birds recognised from previous days. On the final day of the study, when different people approached the nests, the birds stayed calm until the person was about to touch the nest.

The mockingbirds seemed to recognise individuals after just two bad encounters, a skill that Levy suspects is rare among bird species. Pigeons need extensive training to recognise different people.

"Sixty seconds of exposure was all it took for mockingbirds to learn to identify different individuals and pick them out of all other students on campus," Levy said.

Mockingbirds may thrive in urban environments by having good perceptual powers that allow them to cope with the complexities of living in heavily populated cities. For example, they might be better at differentiating between cats that are aware of their nests and those that are simply passing by.

A mockingbird dive-bombs a student volunteer in an attempt to drive her away from its nest. Photograph: Lou Guilette/PNAS

"We don't believe mockingbrids evolved an ability to distinguish between humans. Mockingbirds and humans haven't been living in close associatioon long enough for that to occur. We think instead that our experiments reveal an underlying ability to be incredibly perceptive of everything around them, and to respond appropriately when the stakes are high," Levy said.

