Relative energetic cost of infant care in small-bodied neotropical primates and its relation to infant-care patterns

Small neotropical primates display an array of infant-care patterns, including maternal care, paternal care, and care by non-mothers, both male and female. The high energetic cost of infant care has frequently been proposed as the primary determinant of the need for caregivers other than the mother in these species. This report examines the evidence regarding cost associated with infant care in Aotus, Callicebus, Saimiri, Callimico, Saguinus and Callithrix genera with adult weights of less than 2 kg. The energetic costs of lactation (estimated from infant growth data) and transport (estimated from relative infant weight and travel patterns of each species) are lowest for Aotus and Callicebus, highest for Saguinus and Callithrix (when they rear twins), and intermediate for Saimiri and Callimico. When these costs are compared to the extent that mothers relinquish care to others, there is no clear relation; that is, the energetic cost of infant care is a relatively poor predictor of the apparent "need" for additional caregivers. Additional factors are proposed which better explain the infant-care patterns displayed by these species; these factors include (1) differences in the relative cost that infant care places on foraging efficiency. These differences are proposed to relate to differences in need for concealment as an anti-predator strategy; (2) differences in availability of suitable helpers; (3) differences in nursing frequency, such that the smallest, fastest growing species are more limited in the extent to which mothers may relinquish infant carrying to others. © 1994 Wiley-Liss, Inc.