Aspects of the behavioural ecology and sociobiology of the pronghorn (Antilocapra Americana)
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AbstractThis is a comprehensive analysis of the behavioural ecology and sociobiology of the pronghorn. It is hypothesized that climate, availability of food, predation and the open structure of the plains habitat are the major ecological selection forces. The general form of adaptations used during the birth process, over the growing season and over the lifetime is predicted by the interaction of the basic biological requirements of a medium-sized ruminant with the ecological forces. The predictions are tested by analysis of behavioural, morphological and reproductive characteristics. Behavioural data on the birth process and social organization were gathered at Wind cave National Park, South Dakota. Data on social organization were analyzed by a computer mapping system. The hypothesis accurately predicted the prominent life history features. The behavioural ecology of birth can be explained by predation and weather. Does and fawns completed the necessary physiological and behavioural processes rapidly and used variations in habitat structure for concealment. Hypothermia was counteracted by maternal drying and ruffling of neonatal pelage. Social behaviour patterns rely heavily on vision for communication, as was expected from the open iii habitat structure. The territorial social organization of one population was explained by competition for food and different strategies of male and female ruminants in a polygynous mating system. Territories were economically defendable. Availability of food was considered a primary ecological force, with habitat structure and predation secondary forces. The change from a territorial social organization to herds of mixed sexes at the beginning of winter may be due to the halting of plant productivity and an increase in predation pressure. Formation of mixed herds may be facilitated by male and female mimicry. Males lose their horn sheaths in early winter. Females have small horns and varying amounts of black hair on their rostrums. Sexual dimorphism in body size is conservative when compared with territorial African gazelles. The relatively long gestation period enables the female to give birth in the spring and to insure insemination by territorial males to obtain the best genes for her eggs and avoid harassing courtship from non-territorial males. Since territories are economically defendable only during the growing season, females come into estrous at that time. Climatic variability may explain why females give birth to two young.
Bibliography: p. 345-363.