The Effects of Social Factors and Kinship on Co-sleeping of Black-and-Gold Howler Monkeys (Alouatta caraya)

Abstract

Group cohesion at sleeping sites may have multiple functions in nonhuman primates, such as facilitating behavioral thermoregulation, social interactions, and reducing the risk of predation. Social, genetic, and ecological factors influence association patterns during sleeping. We explored the effects of sex, age class, association during diurnal activities (feeding, moving, resting, and social interactions including play, grooming and howling), and kinship on sleeping cluster associations in a wild population of black-and-gold howler monkeys (Alouatta caraya). We collected behavioral data (mean = 471 ± SD 34 observation hours/study group) and 29 fecal samples for genetic analysis from four groups inhabiting San Cayetano (27°30′S–58°41′W), Corrientes, Argentina, for 1 yr (June 2012–May 2013). Our results showed that black-and-gold howlers preferred to sleep in clusters, and that the composition of these clusters was affected by age class, diurnal social interactions, and kinship. The probability of sleeping in clusters decreased with increasing age of the individual. Association during daytime activities (feeding, moving, and resting) was a significant predictor of nocturnal grouping. Dyads composed of mother–offspring, siblings, and individuals that were not closely related to one another showed a high frequency of association for nocturnal sleep. Father–offspring dyads did not show statistically significant values of nocturnal associations. This study highlights the social function of sleeping in clusters and suggests that primates develop a set of strategies that favor social affiliative relationships between individuals in a nocturnal context.