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Inter and intraspecific behaviour of Eumetopias Jubatus and Zalophus Californianus on a winter haulout area Brenton, Clayton Mearle


An ethogram of 37 behaviour patterns is used to describe inter and intraspecific interactions of five age-sex classes of Eumetopias jubatus and two age-sex classes of Zalophus californianus on a winter haulout area. Larger-older sea lions are dominant to smaller-younger ones, with male E. jubatus dominant to female E. jubatus and male Z. californianus. The behavioural sequences which are used for establishment and maintenance of dominance, and which are important for energy conservation on the breeding rookery, are learned on the non-breeding haulout areas-Challenging and interacting with dominants affords subordinates the opportunity to "move up" the hierarchy relationship and to expand their behavioural repertoire. Older males predominantly use non-body contact displays during interactions. Younger males use more physical body contact behaviour than display behaviour. The majority of extended Z. californianus interactions are in water a few meters deep, whereas E. jubatus males generally joust on land or in water less than one meter deep. When Z. californianus males mimic E. jubatus males during an interaction, an increase in physical aggression is observed for the Z. californianus partner. A lack of metacommunication between the two species was observed on several occasions. As a result of an energy "trade-off", older E. jubatus males occupy a slightly less environmentally preferred area than do other male classes. Females are forced from the environmentally preferred areas by harassment from young E. jubatus males. Zalophus californianus classes are influenced by weather to a greater extent than are E. jubatus classes and do not haul out in areas exposed to chilling winds. The reduced aggressive level of Z. californianus males, as opposed to E. jubatus males, allows individuals of the former species to crowd together and retain body heat during cold weather. Females appear to induce territorial behaviour in old bulls. Pups appear to induce territorial behaviour in lactating females.

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