Feral, untrained pigeons can recognise individuals and are not fooled by a change of clothes, according to a study.
Scientists have shown that urban pigeons that have never been caught or handled can recognise individual people, probably by using facial characteristics.
Although pigeons have shown remarkable feats of perception when given training in the lab, the new study is the first research showing similar abilities in untrained feral pigeons.
One individual simply ignored the pigeons, allowing them to feed while the other was hostile, and chased them away.
This was followed by a second session when neither chased away the pigeons.
The experiment, which was repeated several times, showed that pigeons were able to recognise the individuals and continued to avoid the researcher who had chased them away even when they no longer did so.
Swapping lab coats during the experiments did not confuse the pigeons and they continued to shun the researcher who had been initially hostile.
Dr Dalila Bovet a co-author of the study from the University of Paris Ouest Nanterre La Défense, said: 'It is very likely that the pigeons recognised the researchers by their faces, since the individuals were both female and of a similar age, build and skin colour.
'Interestingly, the pigeons, without training, spontaneously used the most relevant characteristics of the individuals - probably facial traits - instead of the lab coats that covered 90 per cent of the body.'
She said the fact that the pigeons appeared to know that clothing colour was not a good way of telling humans apart suggests that the birds have developed abilities to discriminate between humans in particular.
Dr Bovet added: 'This specialised ability may have come about over the long period of association with humans, from early domestication to many years of living in cities.'
She said future work will focus on identifying whether pigeons learn that humans often change clothes and so use more stable characteristics for recognition, or if there is a genetic basis for this ability, linked to domestication or to having evolved in an urban environment.
The findings were presented at the Society for Experimental Biology Annual Conference in Glasgow.
Crows also have an excellent memory for human faces - and can tell the difference between a friendly face and a dangerous one.
The birds - which are said to be as intelligent as chimpanzees - will remember the face of someone who poses a threat to them for at least five years.
Dr John Marzluff, of the University of Washington, said: 'Our findings add to the evolving view of large-brained, social and long-lived birds like crows being on a cognitive par with our closest relatives.'
A team of scientists from the university exposed crows in Seattle to a 'dangerous face' by wearing a mask while trapping, banding and releasing birds at five sites.
Over a five-year period after the trapping had stopped, they found that the mask received an increasingly hostile response from birds in the area – suggesting that the captured birds had been able to warn others.
