Mother and sibling discrimination at a distance by three- to seven-day-old lambs.

This study examined some aspects of the developmental phase of social bonding in newborn lambs. In Experiment 1, 3-day-old Merino lambs (singles and twins) were tested in a 2-choice situation for mother discrimination at a distance. In Experiment 2, the ability of twins to discriminate their siblings at a distance was studied 3 and 7 days after birth. When released at 9 m from two postparturient ewes after a latency of 30 s, which allowed the lambs to hear and to see both animals, most lambs chose to run and to stay with their own mothers before the end of the 2-min test (Experiment 1). There was no difference between singles and twins, nor between males and females in their distant discriminative ability. However, twins were initially undecided, slower to reach their mothers, and spent significantly less time with them. When the same testing procedure was used for sibling discrimination, most 3-day-old twins went to a lamb, but the proportion of lambs reaching the sibling first did not differ significantly from random, and the time spent near either lamb was similar (Experiment 2). During these tests, female lambs performed better than males. When tested 7 days after birth, all twins reached a lamb and a high proportion of them chose to go to the sibling first. They also spent most of the time near it. These results demonstrate that mother discrimination from a distance is well established in 3-day-old lambs and sibling discrimination takes longer to develop but has occurred by 7 days of age.