The ability to recognise faces is one of the most important human social skills. People recognise familiar faces easily, and can identify unfamiliar faces from repeatedly presented images.
As with some other animals such as dogs and monkeys, sheep are social animals and can recognise other sheep as well as familiar humans. But little is known, however, about their overall ability to process faces.
Researchers from Cambridge's Department of Physiology, Development and Neuroscience trained eight sheep to recognise the faces of four celebrities from photographic portraits displayed on computer screens.
Training involved the sheep making decisions as they moved around a specially-designed pen.
At one end of the pen, they would see two photographs displayed on two computer screens and would receive a reward of food for choosing the photograph of the celebrity, by breaking an infrared beam near the screen. If they chose the wrong photograph, a buzzer would sound and they would receive no reward. Over time, they learn to associate a reward with the celebrity’s photograph.
After training, the sheep were shown two photographs – the celebrity’s face and another face. In this test, sheep correctly chose the learned celebrity face eight times out of ten.
In these initial tests, the sheep were shown the faces from the front, but to test how well they recognised the faces, the researchers next showed them the faces at an angle.
As expected, the sheep’s performance dropped, but only by about 15 per cent - a figure comparable to that seen when humans perform the task.
Finally, the researchers looked at whether sheep were able to recognise a handler from a photograph without pre-training.
The handlers typically spend two hours a day with the sheep and so the sheep are very familiar with them. When a portrait photograph of the handler was interspersed randomly in place of the celebrity, the sheep chose the handler’s photograph over the unfamiliar face seven out of ten times.
So would the ability allow sheep to pick out sheep rustlers in a line up? Researchers think not.
"I don’t think sheep are going to become important police witnesses someho," added Dr Morton. "They might recognise somebody, but how could you test that? I don’t think it would be feasible.
"Future studies might use emotional responses to faces in sheep to study, for example, stress. One could ask, does a stressed sheep respond differently to a human face."
The research was published in the journal Royal Society: Open Science.