London: Pigeons are cleverer than you thought -- they never forget a face, say researchers. A new study by the University of Paris has shown that even feral and untrained pigeons can recognise individuals -- probably by using facial characteristics -- and are not fooled by a change of clothes.

Although pigeons have shown remarkable feats of perception when given training in the lab this is the first study showing similar abilities in untrained feral pigeons, say the researchers.

In a park in Paris city centre, pigeons were fed by two researchers, of similar build and skin colour, wearing different coloured lab coats.

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, a website reported.

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 shun the researcher who had been initially hostile.

"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," said Dr Dalila Bovet, who led the study.

"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," Bovet added.

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.

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.

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, say the researchers.