Abstract: Used duration of social-investigatory behavior by 36 mature male Long-Evans rats as a measure of individual recognition in 5 experiments to assess social memory. In Exp I, the duration of social investigation during a 2nd exposure to the same juvenile (n[en space]=[en space]12) was directly related to the length of the interexposure interval. In Exp II, Ss were exposed to the same or different juvenile 10 min after an initial 5-min exposure to a novel juvenile; reexposure to the same juvenile elicited significantly less social investigation than an exposure to a different juvenile. Exps III and IV demonstrated that following a 5-min introductory exposure, social memory of the juvenile was relatively brief in comparison with that of mature Ss. Exp V revealed a retroactive interference effect on recently acquired memory for an individual: 12 mature Ss exposed to interpolated social experience engaged in significantly longer investigation of a juvenile than those with no interpolated social experience. The combined results suggest that (1) the rat normally engages in spontaneous learning of individual identity and (2) social memory may be a significant aspect of complex social interactions. (16 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved)

Abstract: Social interactions between individual horses were observed in two herds each comprising a stallion and a number of mares. In one herd, the animals were observed whilst grazing and resting; in the other, nearest neighbours were recorded when the animals were grazing, and social interactions were noted when the animals were feeding on hay.
In both herds, the horses showed marked preferences for the company of specific individuals when they were grazing. In one herd, the associations were mainly between individuals that had been associated prior to being put in the herd. In the other herd, this was not the case. A new statistic was produced for testing for specific company preference. In both herds, the stallion was dominant over all mares and never received any aggression.
The complete social hierarchy could not be determined for the herd which was observed only when grazing because social contact was restricted to that within groups or pairs that associated together. In the herd to which hay was fed, a non-linear hierarchy existed. Statistics were produced to quantify both the general level of dominance of a horse and its specific dominance or subordination to every other horse. It is suggested that these statistics, and one for quantifying the general aggressiveness of a horse, could be widely used.
A principal component analysis allowed the horses to be characterised socially according to aggressiveness, their attitude to other horses and their attractiveness to other horses.