The breeding biologies of the Petrels Pterodroma macroptera, P. brevirostris and P. mollis at Marion Island

Abstract

The Great-winged Petrel Pterodroma macroptera, Kerguelen Petrel P. brevirostris and Soft-plumaged Petrel P. mollis breed in different habitats at different times of the year at Marion Island. P. macroptera breeds in inland slopes during winter, brevirostris breeds in flat marshy areas during early summer and mollis breeds during late summer in coastal slopes. Nesting-burrows of macroptera and rnollis have a similar simple design but burrows of brevirostris have a drainage system to cope with their waterlogged breeding habitat.

Incubation periods are similar (56, 49 and 50 days in macroptera, brevirostris and mollis respectively), but fledging periods are very different (61 days in brevirostris and 91 days in mollis). The species rear chicks at different times, presumably to help reduce interspecific competition for food. In all species, the chicks are fed mostly squid, but meals of brevirostris chicks contain most crustaceans and fish. Differences in quality of meals in part explain the faster growth of brevirostris compared to macroptera or mollis. The timing of breeding influences the vulnerability of each species to predators, which is reflected in differences in breeding success (53%, 7% and 0% in brevirostris, mollis and macroptera respectively).