Few aspects of primate behavior are so intriguing, yet so poorly understood, as the intense care of infants by males. And nowhere among primates is paternal care more extensive than among owl monkeys. Owl monkeys are small, arboreal primates of Central and South America who live in groups with only one reproducing male and one reproducing female. In these monogamous groups, the father is the main provider of infant care, transporting, playing, sharing food and grooming the infant more than the mother. Since 1996, the Owl Monkey Project of Argentina has evaluated hypotheses on the evolution of social monogamy, infant care, and pair bonding in humans and non-human primates. Why do male owl monkeys mate in a monogamous relationship presumably foregoing other reproductive opportunities? Why do they provide so much infant care? The birth of two sets of twins for the first time in 15 years, offers the possibility of further evaluating the hypothesis that males' contribution to infant care reduces the mother's energetic costs. During a 6-month period, this study will characterize the development of the two set of twins and will describe the behavioral interactions between twins and parents, twins and siblings, and parents and older young. Results from this study will be used for comparison with similar data collected over the years in groups with singletons. The study will expand the broad impacts of the Owl Monkey Project. Being the only long-term program on any mammal species in the Argentinean Gran Chaco, the project has multiplying effects on the conservation of this ecosystem and its fauna. It also promotes the development of biological anthropology through the participation over the years of more than 200 students (52% females, 48% males) from the US (100 students), Argentina (120 students) and 14 other countries (30 students).
The Owl Monkey Project of Argentina has provided over the last 16 years crucial information on the behavior, demography and reproductive ecology of owl monkeys, a small neotropical monkey, and one of the few socially monogamous primates in the world. Owl monkeys offer unique opportunities to evaluate hypotheses on the evolution of social monogamy, infant care, and activity patterns among primates. Why do male owl monkeys mate in a monogamous relationship presumably foregoing other reproductive opportunities? Why do male owl monkeys invest so heavily in the care of offspring? Why are owl monkeys the only anthropoids with nocturnal habits? When addressing those questions, the Owl Monkey Project is helping us understand how ecological and social factors regulate social monogamy and infant care in primates, including humans. It is also allowing us to examine some of the environmental factors that may have been key in triggering evolutionary switches between diurnal and nocturnal habits in primates. Field work takes place primarily in Estancia Guaycolec, a 25,000 ha cattle ranch in the Province of Formosa in the Argentinean Chaco. In the last few years, the work has been expanded to Pilcomayo National Park (58,000 ha), the only park in Argentina where owl monkeys are protected. A Field Station in the city of Formosa, owned by the University of Pennsylvania, houses the project offices, labs, and lodging facilities, whereas the local not-for-profit organization Fundación ECO provides logistical and administrative support. The Centro de Ecología Aplicada del Litoral (CONICET, Argentinean National Council of Research), the National Parks Administration and the Department of Anthropology of the University of Pennsylvania all provide institutional support. In late 2011, when the first two sets of twins in 16 years of research were born in the population, a fantastic opportunity arose to investigate questions relating to the care of infants taking advantage of an unusual natural situation. The reproductive effort that parents make at a certain time strongly influences their future reproductive success. Hence, in species habitually bearing singletons, one expects that the occurrence of twins should pose considerable energetic costs on the care-takers. We expected that these increased costs associated with twinning would lead to changes in the care-givers' behavior, and/or to differing developmental rates in twins when compared to singletons. Following the birth of the twins we collected data on food availability and behavioral data on infant care. We used those data to compare them with data collected earlier from groups with singletons. We found that 2011 was a good, but not extraordinarily good year in terms of food. Twins, like singletons, were carried nearly exclusively by the male, and they were carried slightly more than singletons. There were apparent increased costs for the parents as reflected in changed time-budgets and an increased group travel-"speed" when compared to singleton groups and groups with no offspring. Our results suggest a relatively inflexible infant care pattern in owl monkeys that largely depends on the care provided by the father. The broader impacts that the Owl Monkey Project has are numerous. Being the only long-term program on any mammal species in the Argentinean Gran Chaco, it has multiplying effects on the conservation of this ecosystem and its fauna. During this past year, the birth of the twins generated some important media coverage both locally and in the US, and those media opportunities were used as educational opportunities. In the future, the most ambitious conservation plans are those related to the National Program for the Conservation of Owl Monkeys that we launched in 2006 with the National Park Administration and the National Directorate of Wildlife and the purchase of land for the definite establishment of an Owl Monkey Reserve. The project also contributes to Anthropology Training in Latin America. There is a major need of formal training in biological anthropology in Latin America, where the subdiscipline is, for the most part, not even recognized as such at universities. Studies like the one on which this report is based provide opportunities for the training of Argentinean students who participate in the project as assistants. But it is not only Argentinean students who benefit from the project, the Owl Monkey Project has made possible the successful participation in biological anthropology research of over 100 students from the US, with a significant participation of undergraduate students from groups under-represented in the sciences.
