Changes in body mass of expectant male cotton-top tamarins (Saguinus oedipus).

It has been noted that expectant cotton-top tamarin males in captivity experience a body mass increase during the last months of their mates' pregnancies, and this has been explained as being a male physiological response. We studied the body mass of 4 inexperienced and 4 experienced expectant males, and we expected to observe a larger body mass increase among the experienced ones since they undergo multiple hormonal changes in comparison to inexperienced expectant males. However, while inexperienced expectant males gained body mass during months 4-6 of the pregnancy period by a mean +/-SD of 5.4 +/- 3.1% (i.e. 29 +/- 17 g), the experienced ones did not (mean +/- SD of months 4-6, 0.5 +/- 1.7%, i.e. 5 +/- 12 g). The results suggest that other factors, such as behavioural communication between pairs and feeding and resting behaviour, should be studied in order to clarify the basis of this body mass increase.