Behaviour and reproduction of Goeldi's monkey Callimico goeldii were studied over a 5-year period at the Jersey Wildlife Preservation Trust. The investigation comprised a study of female reproductive hormones during pregnancy and the non-pregnant phase; a study of pair bonding in newly-established pairs, long-established pairs and breeding pairs rearing infants; a study of bonding in experimentally established male-female-female trios; and a study of infant rearing.
The major urinary oestrogen metabolite was oestrone-3-glucuronide, and it was a good indicator of ovarian cycles and pregnancy. Ovarian cycle length was 24.1 ± 0.9 days. Gestation length was 145-152 days. Female proceptive behaviour was significantly elevated during ovulatory periods, but no significant change in male sexual behaviour was found across the female cycle, possibly indicating that ovulation was hidden from the male. In two of the three male-female-female trios both females conceived, but infants were reared in only one trio. In the third trio, reproductive suppression of the subordinate female occurred. All three trios were disbanded following serious fights between the females.
Bond-promoting behaviour was primarily performed by the male and was reduced significantly in established pairs compared to new pairs. During the first six weeks of infant rearing bond-promoting behaviours were elevated almost to those of new pairs, although the infant, rather than the female, may have been the focus of the male's attention. There was little evidence for a lasting pair bond. In the male-female-female trios, the male associated with one female more than the other as measured by approaches, time in proximity and grooming. The preferred female was not necessarily the 'winner' of the fight between the two females.
The female was the predominant infant caretaker, undertaking exclusive care for three to seven weeks. Even after extra-maternal care began, the female remained the major caretaker. Use of maternal time-budget modelling suggested that seven weeks may be the maximum time that a female can rear the infant unaided, coinciding with the approximate time of doubling of infant body mass. There was no evidence of competition among carers to carry the infant and most transfers were infant-initiated. The benefits of extra-maternal care were discussed.
Allometric analysis of New World monkeys showed that Callimico may be unique in having a single relatively small infant. The other species considered have either a relatively large single infant, or two relatively small infants. Theories concerning the evolution of twinning among the Platyrrhini were discussed
