Abstract: Discriminative learning abilities were studied in 12 mature, malnourished horses. All horses initially received a condition score (CS) between 2 and 4 on a scale of 1 (poor) to 9 (extremely fat). Then horses were assigned to one of 3 treatments based on their eventual, rehabilitated CS during discrimination testing: thin, CS 1-3; moderate, CS 4-6; and fat, CS 7-9. The discrimination learning task was performed for 14 days with a maximum of 20 trials per day. Daily criterion was set at eight consecutively correct trails. Total trials to first criteria and total errors during testing were recorded. Analysis of variance showed that treatments did not differ (P>0.05) in total trials to first criterion, however horses on the fat treatment did have higher total error scores (P<0.05) than horses on the thin or moderate treatments. This difference was probably owing to lack of motivation in the fat treatment horses, rather than to true learning ability differences. The sex of the horse did not significantly affect either learning score.

Abstract: Feral pony mares, Equus caballus, at Assateague Island, Maryland, formed linear dominance hierarchies within bands. Generally, older mares dominated younger mares, and larger mares dominated smaller mares. Large mares initiated aggression more often than small mares when age was controlled for but, surprisingly, older mares initiated aggression less often than younger mares when size was controlled for. Thus, mares peak in aggressiveness fairly soon after achieving full size and then, while maintaining or improving their rank in the domainance hierarchy, progressively reduce their involvement in aggression as they grow older, Involvement in aggression per mare increased as number of mares in the group increased; this effect was independent of nearest-mare distances. Frequency of involvement in aggression did not differ between mares that had changed bands within the year and mares whose band association had continued for a year or more. Aggression was directed more frequently than expected at subordinate mares who were nursing, and also occurred more frequently than expected at water holes. The proportion of aggressive encounters during grazing closely matched the total proportion of time spent grazing. Subordinate mares with foals received aggression more often than subordinate mares without foals. The high frequency of aggression associated with foals and nursing suggests that interference with reproduction of subordiantes is an important mode of competition between mares. Such interference may be common in animals that feed on dispersed resources and live in small, cohesive groups.

Abstract: Individuals in a foraging group of brown capuchin monkeys choose different spatial positions relative to the rest of the group. An individual's choice of spatial positiion affects its foraging success and perceived predation risk (as measured by vigilance behaviour). The two most dominant group members preferred to forage where their expected forwaging success was greatest. Juveniles chose to forage where their perceived predation risk was least, not where they would achieve the highest foraging success. The positions used by non-dominant adults neither maximized foraging success nor minimized predation risk. It is likely that subordinate adults accept spatial positions with suboptimal ecological consequences to avoid the costs of frequent confrontations with the dominant members of the group over foraging sites in poreferred positions.