Establishment of vocal communication and discrimination between ewes and their lamb in the first two days after parturition.

In sheep, the mother-young relationship is characterized by an exclusive bond that relies on the rapid establishment of mutual recognition. However, the role of acoustic cues has been underestimated and neglected in this early discrimination. Therefore, the aim of the present study was (1) to characterize the vocal behavior of ewes and their lambs during the first 15 days postpartum and (2) to investigate the ability of newborn lambs and their mothers to discriminate each other from alien subjects within the first 48 hr postpartum on the basis of acoustic cues only. Ewes started to vocalize in the last 3 hr preceding parturition, emitting mainly high-pitched bleats. However, the bleating activity was highest during the first 3 hr following birth, consisting mainly of low-pitched bleats. Thereafter it decreased sharply until 24 hr postpartum, with most of the activity coming from the mother. In a two-choice test, ewes discriminated their own from an alien lamb on the basis of acoustic cues only at 24 hr postpartum, while lambs did so for their mother at 48 hr, which in both cases was much earlier than reported so far. We conclude that early vocal recognition between the ewe and her lamb may play an important role for the maintenance of mother-young contact.