Inter-population segregation in the wintering areas of macaroni penguins

How top avian predators are distributed at sea during the inter-breeding period remains poorly known. Here we focused on the pelagic seabird that is the single greatest avian consumer of marine resources: the macaroni penguin. Our aims were (1) to investigate where these penguins are distributed whilst at sea during winter, and (2) to determine how their distribution and trophic ecology varies in 1 colony between successive years and between 2 colonies from neighbouring localities at the same time. We surveyed a total of 30 penguins from Crozet and Kerguelen Islands (southern Indian Ocean). Penguins from Kerguelen were tracked in 2006 and 2007, and those from Crozet in 2007. Habitat use was investigated using miniaturised light-based geolocators, and trophic ecology by the use of stable isotope analyses. Results showed large-scale patterns of distribution over deep oceanic waters of the Polar Frontal Zone characterised by a temperature of 3.0 to 3.5 degrees C during July. Birds from Kerguelen had a consistent inter-annual winter distribution at the population level. Birds tracked from Crozet were distributed in distinct areas, separate from the birds from Kerguelen. Trophic ecology (blood delta N-15 value) was very similar between years and colonies, and indicated that these penguins preyed upon low trophic level prey, most probably swarming crustaceans, at the end of winter. We conclude that inter-annual fidelity in winter habitat provides evidence of highly favourable and predictable foraging areas, while the distinct inter-colony distributions suggest very heterogeneous distribution of profitable feeding areas for this species in the southern Indian Ocean.