Huemul (Hippocamelus bisulcus) sociality at a periglacial site: sexual aggregation and habitat effects on group size

I studied social organisation of the huemul (Hippocamelus bisulcus), an And ean deer, during spring in coastal Chile. Analyses are based on individuall y recognised adults without young of the year. Deer that were not alone gen erally joined groups containing both sexes, and the proportion of time indi viduals spent in mixed-sex groups increased with the individual's mean grou p size. The absence of sexual segregation during spring is unusual among se xually dimorphic ungulates, and possibly reflected little variability in fo od distribution and (or) sex-specific predation pressure. Group sizes of in dividuals observed on multiple days increased strongly with distance from r ocky slopes, and this relationship appeared to be unaffected by food distri bution. These results suggest that the risk of predation, probably from cou gars (Felis concolor) and (or) human hunters with dogs (Canis familiaris), is lower on rocky slopes than in valley-bottom habitats. Group sizes of ind ividuals seen only once, however, were independent of distance from rocky s lopes, possibly because these individuals were transients that did not inte grate into the social structure of resident deer. The effect of rocky slope s on group sizes of individuals observed on multiple days is more character istic of mountain Caprinae than of deer. The huemul is endangered, and its extinction could represent a substantial loss in the behavioural diversity of the Cervidae.