The role of familiarity in the development of social recognition by lambs

A series of experiments investigated the role of association and familiarit y in the development of social recognition among lambs. In each experiment, lambs were rested successively with 2 different social partners. When sepa rated from their mothers, lambs that were paired with a partner with which they had been housed for 17 or 5 days emitted fewer distress bleats than th ey did during tests with an unfamiliar lamb. However, this effect was only evident when the test with the unfamiliar partner preceded the test with th e familiar partner. When lambs were first tested with an unfamiliar partner treated with the same artificial odorant that had previously been associat ed with members of their own group. they bleared more than they did during a second test with a partner whose odor was novel. This effect was not obse rved when the familiar- and novel-odor partners were encountered in the rev erse order. Bleating frequencies by lambs paired with their twin did not di ffer reliably from those of lambs paired with a familiar non-twin. Nonethel ess, there was a significant correlation between the number of bleats by tw ins that were tested together. Overall, the results indicate that lambs bec ome familiar with and recognize individuals (twins and non-twins) as a resu lt of direct association. Lambs also discriminate between novel scents and artificial odorants associated with their familiar agemates, but such odors neither mask nor substitute effectively for lambs' individually recognizab le phenotypes. Bleating frequency increases with the novelty of the social partner and of the test situation, and is therefore markedly affected by re peated testing.