Aggregation and dispersion of female New Zealand sea lions at the Sandy Bay breeding colony, Auckland Islands: How unusual is their spatial behaviour?

摘要

We investigated the spatial behaviour adopted by female New Zealand sea lions, Phocarctos hookeri, at the Sandy Bay breeding colony in 2002 and 2003. Each breeding female exhibited a spatio-temporal behaviour based on two phases: breeding and dispersion. The breeding phase, typical of all otariids, led to the formation of the breeding aggregation where all pupping took place. Each female later moved outside the breeding area and entered a dispersion phase. The female population spread inland, and progressively decreased as females took their pups away from Sandy Bay. Pup survival was not affected by this spatial behaviour though the year had an effect. A larger population size during one year may have created a dilution of male aggressiveness and resulted in fewer movements of females. Females that had to move more during the pupping day were found to be more likely to lose their pups. Although a few studies have shown that mother and pup pairs of other species may exhibit dispersal after breeding, the observed terrestrial dispersion phase of the female New Zealand sea lions has never been reported for any other pinniped species and is likely unusual.