Characterization of the oestrous cycle and mating season of squirrel monkeys from copulatory behaviour

Abstract

Observations of the behavior of squirrel monkeys [Saimiri sciureus], including 8 opposite-sex pairs during daily 30 min social encounters and 2 mixed-sex permanent groups during daily 30 min observations sessions, over a 14 mo. period were used to determine the periodicity of the estrous cycle and annual mating season. The median and modal length of the estrous cycle was 8 days, within which copulations were limited to a 1-2 day period. In a cyclic female, plasma progesterone levels over a 24 day period dropped from 85-151 ng/ml to 25 ng/ml 2 days before estrus. In non-cyclic females plasma progesterone values were < 15.4 ng/ml. Males exhibited a 6.8-19.7 wk season of copulation and ejaculation. The onset of this mating season in Aug. coincided with the annual peak in male body weight (the ''fatted male'' phenomenon).