Terrestrial habitat use of male northern and southern giant petrels breeding at Marion Island

Abstract Coexisting species reduce direct competition by partitioning resource use through mechanisms such as spatial and temporal segregation, as well as dietary specialization. Northern giant petrels (Macronectes halli) and southern giant petrels (M. giganteus) are closely related seabirds that coexist on some Southern Ocean islands. Breeding male giant petrels often scavenge seal and penguin carrion on land, but their predominantly terrestrial movement patterns and habitat use remain understudied. We used tracking data collected at Marion Island to investigate the terrestrial space use of 28 incubating male northern and southern giant petrels. Our results show that both species exhibit highly localized terrestrial movement patterns. Despite their shared predator-scavenger trophic niche, both species concentrated their terrestrial foraging at a single site, where large numbers of king penguin chicks likely provided abundant foraging resources for male giant petrels during the three study years. The prominence of terrestrial foraging among male giant petrels reduces competition with females and other procellariiforms, but our findings do not indicate strong spatial segregation of terrestrial foraging between males of the two giant petrel species.