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: Dominance-subordinance relationships among a captive group of adule bighorn sheep (Ovis canadensis californiana) were studied from May 1977 to December 1978. Social interactions between females were brief in duration and infrequent. Although a dominance hierarchy was evident among the females, it was not linear. Horn length and body weight were not consistently correlated with social status. The highest ranking females were the most aggressive individuals, initiating more agonistic interactions than subordinates. Females with high social status did not have higher quality diets, lower activity costs, or higher productivity than low ranking females.

Abstract: Opportunities for social learning within a group of animals are likely to be influenced by the social dynamics of that group. Some individuals may be more influential demonstrators than others even when there are no differences in their skill level or performance. In this study of domestic hens,Gallus gallus domesticus, differences in demonstrator salience were examined. From 24 separate flocks we selected as demonstrators a dominant cockerel, a dominant hen, a mid-ranking hen or a subordinate hen. Demonstrators were pretrained to perform an operant discrimination task to obtain food. Six observers from each flock individually watched the demonstrator perform the task for four 5-min sessions held on consecutive days. On the fifth day observers were tested individually in the operant chamber. We analysed data from 19 flocks, where there were no quantitative differences in demonstrator performance. Observer hens of relatively high social status performed more correct operant pecks than observer hens of relatively low social status. Demonstrator category also had a significant effect on subsequent observer behaviour. Hens that had observed cockerels performed very few general pecks or operant pecks. Hens that had observed dominant hens performed more operant pecks, but hens that had observed sub-ordinate hens performed more general pecks in the chamber. The results suggested either that there was an interaction between dominance and gender in demonstrator salience or that dominant hens might have been influential because of some factor imperfectly associated with their dominance status. A possible candidate was the foraging ability of the dominant hens. In a second experiment using the same protocol, we manipulated the prior foraging success of dominant hens from four additional flocks but this had no significant effect on their subsequent influence as demonstrators.

Abstract: Lactating female baboons, Papio cynocephalusoften maintain close associations with particular males. There are at least three proposed benefits of 'friendships' to females: (1) male protection against potentially infanticidal males; (2) male protection against harassment by dominant females; (3) male attachment to an infant that develops into future care of juveniles. These hypotheses were examined in a population of chacma baboons, P. c. ursinusin which male infanticide accounted for at least 38% of infant mortality. Almost all mothers of young infants formed strong bonds with one or two males with whom they had copulated during the cycle in which they conceived their infants. Females were primarily responsible for maintaining friendships during lactation, but they terminated these relationships if their infants died. In playbacks of females' screams, male friends responded more strongly than control males. They also responded more strongly to the screams of female friends than to the screams of control females. Following an infant's death, however, male friends responded less strongly than control males to the same females' screams. Finally, male friends responded more strongly than control males to playback sequences in which female screams were combined with the threat vocalizations of a potentially infanticidal alpha male, but not when female screams were combined with the threat calls of a non-infanticidal male or the alpha female. Both observations and experiments suggest that the benefits of friendships to females derive from the protection of their infants against infanticide.1997The Association for the Study of Animal Behaviour