Social and spatial foraging patterns of the jackass penguin<i> Spheniscus demersus</i>

Abstract

The inshore distribution and foraging behaviour of jackass penguins Spheniscus demersus were studied between December 1982 and August 1983 in waters close to breeding islands in Saldanha Bay, South Africa. The use of a sail-boat permitted close observation of foraging penguins with minimal apparent disturbance. Penguin numbers at sea were lowest in December, when most birds were confined to islands during moult, and highest during the winter breeding season. Although most penguin group sizes were small (one or two birds), over 44% of penguins occurred in groups of more than 10 birds. Three typical penguin group formations occurred at sea: ‘facing-search’, ‘line-abreast’, and ‘pointed-ovoid’. Penguins also foraged in association with other seabirds and marine mammals. The importance of large foraging groups suggests that the jackass penguin relies on shoals of similar sizes to those taken by the commercial purse-seine fishery, increasing the potential for competition.