Transfer between views of conspecific faces at different ages or in different orientations by sheep

Sheep are able to discriminate photographs of conspecific faces. The present study investigates adult ewe's recognition of faces of the same animal between different ages or between different orientations. Twelve adult sheep were first trained to discriminate between faces of two unfamiliar animals, one of which was associated with a food reward. Transfer of discrimination from this pair to the same pair but at a different age, or in a different orientation, was then evaluated (transfer test), and compared with a new pair of the same condition (control test). Learned discrimination of a frontal view of unfamiliar 3-month-old lambs' faces improved subsequent discrimination of the same pair when they were 1-month-old in comparison to discrimination of new 1-month-old faces. Moreover, sheep that were trained to discriminate frontal views of unfamiliar adult individuals discriminated profile views of the same animals more accurately than that of novels. However, learned discrimination of the profile view of unfamiliar adult faces had no effect on subsequent discrimination of the frontal view of that same pair. These results suggest that to some extent sheep recognise faces of unfamiliar animals at different ages and in different orientations.