Birth synchrony in squirrel monkeys (Saimiri oerstedi)

Summary The vigilance behaviors and association patterns of adult female squirrel monkeys (Saimiri oerstedi) in Parque Nacional Corcovado, Costa Rica were studied over the annual reproductive cycle to identify a possible adaptive function associated with the unusually close within-group birth synchrony prevalent in Saimiri populations. Raptor association with the troops, predation attempts, and monthly changes in food abundance were also documented. Seasonal fluctuations in food abundance probably constrained the timing of births among three contiguous troops to a two month period. The close within-troop birth synchrony (majority of births occurring within a week) is suggested to be advantageous because of intense predation pressure on neonate squirrel monkeys. Adult females with neonates cooperate in anti-predator vigilance and defense of neonates. Participation in these maternal associations may increase the probability of neonate survivorship. Variable gestation length in squirrel monkeys may reflect a lability in the duration of gestation to allow coordination of the timing of births among females in a troop.