Dads do not pay for sex but do buy the milk: food sharing and reproduction in owl monkeys (Aotus spp.)

Sharing food is costly, and animals rarely share food with unrelated individuals. Males may share food with females when females are fertile or when female nutrition will affect offspring. Such benefits are known for insects and birds, but not for mammals. This study examined the effect of female reproductive state (ovarian cycling, pregnancy, lactation) on food sharing between mates in monogamous owl monkeys, Aotus spp. Male–female pairs of captive owl monkeys at the DuMond Conservancy (Miami, FL, U.S.A.) were regularly observed feeding from October 2003 to November 2004. To determine the onset and duration of pregnancy, urine was collected from females and analysed for the progesterone metabolite pregnanediol-3α glucuronide using enzyme immunoassay. Food transfers from females to males did not vary across reproductive state, and males did not transfer food most often to females when females could potentially become pregnant. Conversely, females most often begged for food when they were lactating, and males most often transferred food to females when their mates were lactating. Compared to males of polygamous species, male owl monkeys are relatively certain of paternity. In addition to providing infant care directly, male owl monkeys would benefit from ensuring that their mates receive adequate nutrition because it indirectly provides nutrition for offspring by enhancing the quantity and/or quality of the mates' milk.