Demographic characterization and social patterns of the Neotropical pampas deer

The most endangered subspecies of pampas deer Ozotoceros bezoarticus uruguayensis is an endemic cervidae of the Uruguayan temperate grasslands. The aim of our study was to assess the demographic trends, grouping structure and dynamic of this small and isolated population. We surveyed the population during seven years and detected an average of 117 (+ 72.7 SD) individuals (44 censuses). The average population structure observed was 55% adult females, 34% adult males, 10% juveniles, and 1% fawns, with a low recruitment rate of 0.11. The pampas deer is a gregarious cervidae with 62% of individuals being observed within groups of at least three animals. Nevertheless we observed substantial differences on group size and composition based on sex, reproductive status, season and trophic resources availability. The population dynamics showed significant changes around the year in the sexual aggregation-segregation pattern, corresponding with reproductive and physiological status. The mean density on this population (11 deer/ km(2)) is the highest reported for the species. Comparable data, from other populations, showed a significant correlation between density and sex ratio, with a reduction in the proportion of males with higher deer densities. An action plan for this endangered population should include initiatives involving private landowners, and guidelines to improve the deer habitat.