Infant Carrying Behavior in Callitrichid Primates: <Emphasis Type="Italic">Callithrix</Emphasis> and <Emphasis Type="Italic">Leontopithecus</Emphasis>

Care of offspring by individuals other than the mother is ubiquitous in callitrichid primates. In spite of its widespread occurrence, however, there is considerable taxonomic variation in the timing and intensity of parental effort by breeding males and nonbreeding juvenile group members. These differences may be attributable to generic and specifies differences in the costs of reproduction for females or in ecological constraints on travel and foraging. We present data on patterns of infant carrying in social groups of two taxa of callitrichid primates (Callithrix and Leontopithecus) throughout the first 3 months of infant life. We evaluated patterns of care in small groups (two or fewer juvenile or subadult helpers) and in large groups (three or more helpers in addition to the breeding adult male and female). Group size had little effect on levels of maternal carrying effort in either marmosets or lion tamarins, and mothers ceased carrying infants by 3 months of age. Carrying efforts by fathers were significantly reduced in groups with many helpers relative to small groups. Helpers carried at consistent rates during the second and third months of infant life in Leontopithecus while in Callithrix, carrying by helpers peaked during the second month. These results suggest that if helpers reduce energetic demands on lactating females, the mechanism by which helpers reduce these burdens is independent of maternal carrying effort.