Vocal Recognition of Recorded Lambs Voices By Ewes of Three Breeds of Sheep

Abstract

Vocal recognition of lamb's voices by their dams was investigated in Border Leicester, Jacob and Soay sheep, using recordings of lambs voices which were played to ewes simultaneously with presentation of a moving model lamb when the lambs were 15-20 days and 40-50 days of age. The number of bleats made by the ewes during playback of own and alien lamb voices was recorded and then the number of times a ewe bleated in answer to a lamb's bleats within 2 s of hearing the lamb bleat was counted. At both age groups the ewes bleated more in response to recordings of their own lambs than to alien lambs, and answered their own lamb's bleats more than alien bleats. The frequency of the ewes bleats increased more to their own lamb's bleats than to alien bleats. The Soay ewes bleated less than the other breeds and the Jacob ewes were the most vocal.

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

“…This indicates that in a double-choice test situation ewes and lambs are able to discriminate their kin on the basis of acoustic cues (high-pitched bleats in the present study) earlier than what had previously been reported in the literature (Alexander, 1977;Poindron & Carrick, 1976;Searby & Jouventin, 2003;Shillito & Alexander, 1975;Shillito-Walser et al, 1981). There is little doubt that this discrimination in ewes and lambs relies on acoustic cues.…”

“…One possibility is that ewes and lambs learn to recognize the individual acoustic signature of their kin in 24-48 hr, since the existence of such a signature is well established in sheep and it is used at later stages of lactation (Alexander, 1977;Nowak, 1991;Poindron & Carrick, 1976;Searby & Jouventin, 2003;Shillito & Alexander, 1975;Shillito-Walser et al, 1981). Our results may suggest that this is already the case at 12 hr for mothers and at 24 hr for lambs.…”

“…Also, in a two-choice discrimination test performed at 12 hr of age, lambs that were the most vocal at birth also had the best performance in discriminating their mother (Nowak, 1990b). Playback experiments have shown that lambs can be discriminated on the basis of their vocal signature (Poindron & Carrick, 1976;Shillito-Walser, Hague, & Walters, 1981) and that this is the case already at 1 week of age (Searby & Jouventin, 2003). Whether discrimination on the basis of acoustic cues only is established in ewes and lambs before 1 week postpartum has never been investigated.…”

“…As the vocal behavior of sheep may vary between breeds (Dwyer et al, 1998;Shillito-Walser et al, 1981;Shillito-Walser, Willadsen, & Hague, 1982) and since no detailed description existed in the Ile-de-France breed used here, we first carried out a descriptive analysis of the vocal behavior of ewes and their lambs during the first 15 days of lactation. In a second independent study, we employed a two-choice test in which only acoustic cues were available to investigate the ability of ewes and lambs to discriminate their kin from alien equivalent subjects in the first 2 days after parturition.…”

Mother–young vocal communication and acoustic recognition promote preferential nursing in sheep

“…In addition, if the subject emitted more bleats during the rest of the test (1 min after playback of the third bleat), he was given one additional point. A major weight was given to this variable because, in other studies (Shillito-Walser et al, 1981;Searby and Jouventin, 2003), the bleating rate has been shown to be positively correlated with recognition. (v) Reunion of mother and young during the playback or the following minute of observation, ending with sucking: 1 point.…”