TWIN NON-TWIN DISCRIMINATION BY LAMBS - AN INVESTIGATION OF SALIENT STIMULUS CHARACTERISTICS/

A series of experiments was conducted to elucidate the stimuli that me diate twin/non-twin discrimination among 2-3 week old lambs. After bei ng separated from their mother, lambs emitted more distress bleats whe n tested in isolation than when penned with their familiar twin, but s eparated from that lamb by a barrier of evenly spaced wood bars. A sim ilar, albeit weaker effect was found for paired vs isolated non-twins. Twins separated by the barrier bleated less than did the non-twins in this condition. In contrast, bleat rates did not differ when subject lambs were tested in the presence of their twin vs a non-twin on the o pposite side of a solid opaque barrier. Intact lambs in a final experi ment bleated less when tested with their tranquillized twin vs a tranq uillized non-twin agemate. The tranquillized stimulus lambs displayed atypical behavior patterns, including suppression of bleats and reduce d activity levels. These data indicate that full bodily contact, vocal izations or normal behavioral patterns are not necessary for lambs to be recognized by their twin. Rather, twin/non-twin discrimination (and the effect of a twin on the rate of distress bleating) appears to dep end upon visual, and possibly olfactory cues.