Factors associated with birth rate and live birth rate in multi-male breeding groups of rhesus monkeys.

Reproductive records of 284 female rhesus monkeys housed in six multimale corrals at the California Primate Research Center were examined for the birth seasons 1977-1982 to determine possible associations between the probability of birth or live birth and female age, parity, origin, parturition in the previous season, infant birth date, and infant birth date in previous season. Multiple logistic regression analysis was used to identify and quantitate the effects of factors on the probability of birth or live birth, while controlling for the possibly confounding effects of other factors in the model. Females who had infants early in the previous season were 2.5 times as likely to give birth as those who had infants late in the previous season. Females with two or three previous births were 2.1 times as likely to give birth, and those with four or five previous births were 6.7 times as likely to give birth as were females with no or one previous birth. Controlling for other factors (age, parity, and timing of birth in the previous season), corralborn females were 3.3 times as likely to give birth as either wild-caught or domestic-born monkeys not native to the corrals. Domestic-born females who were not corral natives were 0.3 times as likely to have live births as wild-caught females. Births late in the season were 1.8 times as likely to result in live infants as births early in the season.

Brief report: Outbreak of severe aggression in captive Macaca mulatta.

An outbreak of severe aggression occurred among females in a rhesus macaque breeding group at the California Primate Research Center four years after the group was established. During the breeding season in which this occurred, the incidence of injured females in other breeding groups at the Primate Center was significantly higher than in the previous year. This breeding season was the first in which a large number of females reached sexual maturity. The group in which the most severe aggression occurred contained the largest number and proportion of maturing females. Evidence suggests that the simultaneous maturation of a large cohort of adolescent females may be associated with increased levels of aggression, and that this aggression may be intensified by certain aspects of captivity.