Unusual behaviour in grey woolly monkeys (Lagothrix cana): Females breastfeeding adult males

Weaning varies between primate species, usually occurring long before adulthood. Here we report adult female woolly monkeys, Lagothrix cana, breastfeeding adult males. From March to June 2013, a study was conducted on a group of 18 grey woolly monkeys, L. cana, living in an ex situ conservation area. During the observation period, five breastfeeding events between adults were observed. The events involved two adult females and two adult males. Although our findings generally correlate with current literature on allonursing, the nursee far exceeded the expected age. Thus, we propose three hypotheses that may explain the occurrence of this adult nursing behaviour: (1) extended maternal care, (2) opportunistic foraging and (3) forming of alliances. The most likely explanation for our observations is that the female woolly monkeys use breastfeeding to move up or maintain the hierarchy, through alliances with top-ranking males. This study adds to our understanding of a little-studied, endangered primate, as well as the costs and benefits of breastfeeding behaviour.