Infant Carrying in Wild Black-Fronted Saddleback Tamarin Groups With Single and Two Breeding Females

In the cooperatively breeding tamarins and marmosets, helpers aid in the transport of heavy twins (15%-20% of maternal body mass at birth). In the few tamarin species studied so far in the wild, the principal infant carriers are breeding adult males, nonbreeding adults and subadults with considerable variation among individuals in their contributions. While tamarin groups usually include only a single breeding female, but groups occasionally include two breeding females. It is not known if and how the number of breeding females affects individual contributions to infant carrying. We studied the mating system of five groups of black-fronted saddleback tamarins, Leontocebus nigrifrons, in northeastern Peru. Two of the five groups included two breeding females, providing the opportunity to compare patterns of infant carrying in groups with a single breeding female and with two breeding females. Overall, adult males and mothers were the principal carriers. In one group with two breeding females, all adult and subadult group members contributed substantially to infant carrying. In the other group the mother received little help and carried her offspring for > 80% of time. In the former group, both females had copulated with both adult males, while in the latter group the female not receiving help had not copulated with the single adult male of the group. These contrasting patterns of infant carrying highlight the high variability within the cooperative breeding system of tamarins.