Gordon D. Jensen

Sexual behavior in a captive group of pigtailed monkeys (Macaca nemestrina)

Sixteen pigtailed monkeys (Macaca nemestrina) were studied to determine patterns of estrous cycles and sexual behavior. The average estrous cycle lasted 42 days, the average tumescent period 21 days, and the average quiescent period 17 days. Results are consistent with those obtained from studies of individually caged monkeys. The mean length of gestation for five live births was 174.6 days with a range of 167 to 179 days. Patterns of heterosexual, homosexual, and self-oriented sexual behavior are described and quantified.Mating behaviors of Japanese and pigtailed monkeys were compared. Although individual elements of sexual patterns were similar, there were quantitative differences and differences in the temporal patterning of the behavior.

The leader's role in controlling aggressive behavior in a monkey group

An established group of pigtailed monkeys (Macaca nemestrina) was evaluated for aggressive behavior. The four highest ranking members of the group were removed one-by-one. Aggression was higher during all periods when the leader was absent and it decreased when he was returned. The leader male of aM. nemestrina group plays the major role in the control of aggression within the group.

Mother monkeys' (Macaca nemestrina) responses to infant vocalizations.

2 mother monkeys (Macaca nemestrina) separated from their infants, 2 adult females without young and 2 adult males were studied to determine activity (pacing) and vocalization in response to taped monkey calls. Stimulus tapes were prepared from two different calls of each of the two infant monkeys and a call of an adult female monkey. Mother monkeys separated from their infants were always more active and vocal than either non-mother female monkeys or males, and their activity and response vocalizations increased during presentations of infant calls. There was no evidence that mothers responded differentially to the calls of their own infants.

Determinants of dominance hierarchy in a captive group of pigtailed monkeys (Macaca nemestrina)

Eighteen pigtailed monkeys, all strangers to each other, were placed together in a laboratory compound. Two infants were eliminated from the study shortly after group formation. To determine dominance hierarchy aggressive-submissive interactions were observed among the remaining 16 monkeys during 4 periods covering 5 months of group development.Results suggested that 3 factors were basic determinants of dominance hierarchy: body weight for males, estrus for females, and maturity for both sexes.Aggressive-submissive interactions were far more frequent during Period I, the first hour of group formation, but decreased with stabilization of hierarchical order in subsequent periods.Aggressive-submissive interactions were not evenly distributed among all possible pairs in the group, but tended to involve mostly the high-ranking animals. Also, high-ranking animals concentrated their aggression towards more submissive monkeys of their own rank. Because low ranking animals were involved in fewer aggressive-submissive interactions, their rank determination was difficult.

Reaction of monkey mothers to long-term separation from their infants

Five pigtailed monkey mothers (Macaca nemestrina) were separated from their six-month-old infants. Mothers reacted initially with agitation. Eighteen days after separation several behavioral measures suggested depression. Two months after separation all measures returned to preseparation levels and showed no change after infants were reunited with their mothers.