Marmosets (Callithrix jacchus) give birth to infants, usually twins, and the mother can become pregnant again almost immediately, so the female is lactating, to feed the newly born infants, while pregnant. These conditions impose extreme physiological demands upon the mother; all the adult and subadult members of the family help to care for the infants, in many instances, from the day of birth. The adult males and adolescents play a very important role in the care of the infants and in their socialisation.
The effects of carrying infants on the behaviour of the mother and the other caregivers were investigated. Identified members of families of marmosets were observed in the first two weeks after the infant's birth, and again in the fifth to sixth weeks of their life. The movements of the caregivers were quantified, as were the duration of the carrying bouts. Carrying one infant and carrying as a pair were scored individually. Carrying infants was found to have a profound effect upon their mobility and activity levels. The adults, and subadult siblings, tended to carry the infants as a pair rather than consecutively. In this way the caregivers, although burdened by the infants, may be maximising the time spent in enforced in activity by carrying the infants together
