Seasonal variation of the social organisation and diurnal activity budget of the Greater Rhea, Rhea americana, in the Argentinean Pampas

CARRO, MARIANA E.; FERNANDEZ, GUSTAVO J.

EMU

CSIRO Publishing

Año: 2008 vol. 108 p. 1 - 24

0158-4197

We analysed the seasonal variation of group size, composition, and individual behaviour of a wild population of Greater Rheas (Rhea americana) in the Argentinean Pampas. We performed seasonal censuses during an 8-year period, and made focal observations on 59 individuals from different groups to assess the proportion of time spent in vigilance, feeding, walking, preening or resting, and noted the number of courtship displays, copulations and aggressions. Rheas were solitary or in groups from 2 to 35 individuals. Mean typical group size was 7.61, with significant seasonal variation, decreasing during the breeding season (spring), possibly related to harem formation. Typical group size for males decreased in the spring, but was invariant for females all year. During spring individuals spent more time vigilant and less time feeding, and were involved in a major number of courtship interactions. Most aggression (72%) was among males, mainly during winter and spring, suggesting strong intrasexual competition. Social organisation and group dynamic appear to be profoundly affected by the mating system of the Greater Rhea.