Azara's owl monkeys in the Humid Chaco: Primatological long-term studies in Argentina.

Abstract

The Owl Monkey Project started in 1996 as a multi-disciplinary program on the Azara's owl monkey of the Argentinian Chaco. The main goals of the project have been to investigate the evolution of the monogamous mating system and parental care of this species. The project has expanded and, for many years, we have also been exploring the potential relationship between demography, the spatial and temporal distribution of food resources, and the monogamous social organization of the species. Additionally, since 2007, we expanded our studies to include the examination of groups that inhabit two different natural habitat types in the humid Chaco of Formosa Province. In this chapter, we use data from 20 years of study, to elucidate factors underlying the demographic structure of different owl monkey groups inhabiting different types of habitats. The study was conducted in the Estancia Guaycolec (a private 25,000-ha cattle ranch) and in Río Pilcomayo National Park (a 52,000-ha protected area). In each study area, two sub-sets of owl monkey groups could be identified: those within the gallery forests (continuous habitat), and groups in forest patches. Our results confirm that the estimated densities for the private ranch are higher than in the National Park. In contrast, group size, birth rates and age structure were similar between sites. Group sizes, birth rates, and specific densities were larger for gallery forests than for forest patches at both study sites. Our studies contribute to the understanding of the evolution of social monogamy and male care, and also provides information on the demography and habitat use of a species that has been declared a Natural Monument in the Province of Formosa.