Abstract
Between the late 1970s and the mid 1980s there were large decreases in numbers of jackass penguins Spheniscus demersus breeding near the centre of the species' distribution, whereas near the periphery of its breeding range numbers either decreased less severely or remained stable. Similar trends had been observed between the mid 1950s and the late 1970s, with the exception that at some peripheral localities numbers had been increasing. The persistence in regional trends reflects an altered distribution of prey organisms. As most colonies occur at the centre of the species' distribution, overall numbers of jackass penguins have continued to decrease rapidly. Some colonies have been reduced to low levels, increasing their susceptibility to site-specific effects and extinction. The conservation status of the jackass penguin, which is now heavily reliant on two island colonies, is expected to continue to deteriorate until prey is again abundant in the central region. Measures that might alleviate the situation are proposed.
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