Abstract # 2553 Event # 200:

Scheduled for Monday, September 21, 2009 10:30 AM-10:40 AM: Session 20 (Del Mar Room) Oral Presentation


THE EFFECT OF GROUND SUBSTRATE, SEASON, AND RANK ON AGGRESSION AMONG FEMALES IN OUTDOOR CAPTIVE GROUPS OF RHESUS MACAQUES (MACACA MULATTA)

B. A. Beisner and L. A. Isbell
University of California Davis, Anthropology Department, 1 Shields Avenue, Davis, CA 95616, USA
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Captive groups of primates often exhibit higher rates of aggression than wild, free-ranging groups. It is important to determine which factors influence aggression in captivity because aggression can be harmful to animal health and well-being. In this study, we investigated the effect of ground substrate, season, rank, and group size on rates of aggression per female in seven captive groups of rhesus macaques [n=70 females, 1723 focal samples] over 14 months at the California National Primate Research Center. Females living in enclosures with grass substrate were 1.7 times less likely to be involved in intense aggression (e.g., chases and physical contact) than females living with gravel [Poisson regression model: p<=0.001]. High-ranking females were 1.3 times more likely to be involved in mild (e.g., threats and lunges) aggression than lower-ranking females [low rank: p=0.02; mid rank: p=0.002]. Females of all ranks were 1.5-1.9 times more likely to be involved in both intense and mild aggression during the breeding season than other seasons [all p-values<=0.01]. Group size did not affect rates of mild [p=0.67] or intense [p=0.88] aggression. Grass substrate may reduce aggression by encouraging foraging behavior, which may increase inter-individual distances. Although some aggression appears to be natural and unavoidable, i.e., aggression during the breeding season, the well-being of captive macaques can nonetheless be improved by developing grass substrate in outdoor enclosures.