Lambs identify their mothers’ bleats but not a picture of her face

Ewes and lambs develop a strong and selective bond immediately after birth that is maintained throughout the suckling period. The strength and maintenance of this bond are partially dependent on the different sensory signals. However, there is little information about selectivity and clues involved in this bond related to later periods. The aim of this study was to determine the importance of visual and auditory stimuli on the lambs' preference toward their mother or a familiar ewe at the age of 3 months. Twenty-four Corriedale ewes and their single lambs were used in 3 tests on 3 consecutive days. The lambs remained continuously with their mothers apart from the period of the preference test. The 2-choice tests were performed in a triangular testing pen (6.0 m x 6.0 m x 4.4 m), with one stimulus placed in each of 2 small sheds (2.0 m x 1.35 m). The lambs remained 3 minutes into the test area without any interference. In Test 1, the preference of lambs toward a picture of their mothers' face or toward a familiar ewes' face (visual signal) was evaluated. In Test 2, the preference of the lambs for their mothers' or a familiar ewes' bleats (auditory signal) was evaluated. In Test 3, visual and auditory signals (but no physical contact) were permitted, evaluating the preference for the mother or a familiar ewe. The lambs did not display any preference for their mothers' picture (Test 1). In Tests 2 and 3, lambs entered their mothers' proximity zone earlier, remained for longer, and emitted more bleats than they did in the proximity zone of a familiar ewe. In Test 2, lambs also entered more times to their mothers' proximity zone. We concluded that 3-months old lambs display a strong preference for their mother, if only auditory or visual and auditive communication are allowed. Contrastingly, they held no preference toward pictures of their mothers' faces to that of pictures of the face of a familiar ewe, suggesting perhaps that at that age, lambs are unable to recognize pictures of faces as adult sheep are able to do.