Gran Chaco Conservation Program

Owl monkeys, giant armadillos, and giant anteaters, three species on which the Zoological Society of San Diego is focusing research in the Argentinean Chaco, were listed among the 19 priority mammal species for the Chaco Region. Identificaiton of conservation priorities for the mammals of the South American Chaco was one of many results from a five-day workshop attended by Conservation Research Fellow Dr. Eduardo Fernandez-Duque and organized by The Nature Conservancy.

Giant armadillos were singled out as one of the highest conservation priorities, given that they probably live in low densities, require vast ares of land that is fast disappearing to agriculture, and are also threated by hunting. In terms of research, progress was made in laying the groundwork for intensive fieldwork on giant armadillos in 2005. Permits were obtained to begin work at Copo National Park in the Province of Santiago del Estero and Pilcomayo National Park in the Province of Formosa. Copo is the only national park protecting the dry Chaco of Argentina and supports the only viable population of giant armadillos in the country, as well as important numbers of giant anteaters. Pilcomayo is the best protected and largest park of the humid Chaco and supports owl monkeys and giant anteaters.

Ongoing owl monkey research during the last several years had confirmed that owl monkeys are one of the few socially monogamous primates in the world. Monogamous species tend to show very little difference in the sizes of males and females. When males are as large as females, it is predicted that there will be little or no competition among individuals for access to mates. Thus, we were surprised to find that although owl monkeys show very little difference in body mass between males and females, there is intense competition and aggression among both sexes while searching for a mate. Fourteen of the 15 regularly observed owl monkey pairs had at least one of the mates replaced during a three-year period. Mate replacement usually occurred as a consequence of an intruding adult expelling the same-sex resident individuals through aggressive interactions. Twelve of the replaced individuals died and five disappeared, suggesting that the costs of this competition are high, in some cases including severe damage to canines and earlobes.

We also continued to examine the unusual activity patterns of owl monkeys in the Chaco. In collaboration with Dr. Hans Erkert (Tubingen University, Germany), collars were placed on eight owll monkeys to record their activity every five minutes during six months. After that time, the animals were recaptured and the date from the collars downloaded to the computer. The data clearly showed that owl monkeys were active during the day as well as during the night and that most nocturnal activity occurred when the moon was full.

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