Social grouping tendencies and separation-induced distress in juvenile sheep and goats.

Social affinities in juvenile sheep and goats were compared by measuring grouping tendencies and separation-induced distress during experimental encounters with a person in either the presence or the absence of juvenile pen-mates. When tested with pen-mates, sheep spent more time near penmates than did goats. When separated from pen-mates, locomotor activity and plasma corticosteroid titers were higher in sheep, whereas vocal rates were higher in goats. Proximity to pen-mate scores were not correlated with either vocal rates, r = 0.20, or locomotion scores, r = 0.21, recorded when juveniles were tested alone. Proximity to pen-mate scores were correlated with posttest corticosteroid titers, r = 0.70; juvenile sheep spent more time near pen-mates and showed greater adrenocortical responses when temporarily separated from juvenile pen-mates. These findings support the possibility that interspecies differences in emotional reactivity contribute to the differences in grouping tendencies these ungulates display in natural or relatively unrestricted social groups.