SEASONALITY IN SQUIRREL-MONKEYS (SAIMIRI-SCIUREUS), SOCIAL FACILITATION BY FEMALES

The extent to which social living arrangements influenced seasonal cha nges in physiology and behavior was examined in adult squirrel monkeys (Saimiri sciureus). Data were collected over 20 months (encompassing two breeding seasons) from animals that were housed in three mixed-sex social configurations that varied in the number of heterosexual and i sosexual social partners. For both sexes, the presence of multiple fem ales was found to facilitate reproduction. Females housed with other f emales were more likely to exhibit seasonal ovarian cyclicity and tend ed to have higher conception rates. Social facilitation of reproductio n was particularly prominent for subordinate females. The presence of same-sex companions also resulted in reduced adrenocortical output in females during the first nonbreeding season. Tn males, the availabilit y of multiple females increased plasma testosterone levels, except in the presence of more dominant males. Seasonal increases in male weight coincided with increased cortisol levels and were most prominent in s ocial groups containing multiple females. ?The influence of multiple f emales on male seasonality occurred despite the finding that male-fema le interactions were infrequent and, in fact, occurred less frequently when isosexual partners were available. Unexpectedly, affiliative soc ial interactions between same-sex and opposite-sex partners occurred l ess frequently during the breeding season. As expected, behaviors asso ciated with sex tended to increase during the breeding season. Very li ttle agonism was observed during the course of the study and there was no evidence of interanimal competition for mates.