Sheep recognise familiar and unfamiliar human faces from 2D images

31 Jan 2018

One of the most important human social skills is the ability to recognise faces. Humans recognise familiar faces easily, and can learn to identify unfamiliar faces from repeatedly- presented images. Sheep are social animals that can recognise other sheep as well as familiar humans. Little is known, however, about their holistic face-processing abilities. In this study, we trained each of the eight sheep (Ovis aries) to recognise the faces of four celebrities from photographic portraits displayed on computer screens. After training, the sheep chose all 'learned-familiar' faces rather than the unfamiliar faces significantly above chance. We then tested whether the sheep could recognise the four celebrity faces if they were presented in different perspectives. This ability has previously been shown only in humans. Sheep successfully recognised the four celebrity faces from tilted images. Interestingly, there was a drop in performance with the tilted images (from 79.22±7.5% to 66.5±4.1%) of a magnitude similar to that seen when humans perform this task. Finally, we asked whether sheep could recognise a very familiar handler from photographs. Sheep identified the handler in 71.8±2.3% of the trials without pretraining. Together these data show that sheep have advanced face-recognition abilities, comparable to those of humans and non-human primates.