Population-specific wintering distributions of adult south polar skuas over three oceans
Résumé
Migratory routes and the areas used during winter have probably been selected to
maximize fitness by providing favorable environmental conditions outside the breeding season. In
polar environments, because of the extreme winter weather, most breeding species migrate to
encounter better conditions in areas that can differ between and also within species. Using geo -
location sensors, we found that south polar skuas Catharacta maccormicki from 2 distant populations
breeding on the Antarctic continent along the Atlantic and Indian Oceans migrate northward
to winter in tropical Indian Ocean and in temperate North Pacific waters, respectively. Most
individuals from each population winter in different environmental conditions, with water temperatures
ranging from 16 to 29°C. Nevertheless, they have very similar activity patterns, spending
more than 80% of their time on the water, and their feather δ15N values suggest that they probably
feed at similar trophic levels during the molt. During overwintering, the overall and constant low
activity level may be partly imposed by molting constraints, but it also suggests that trophic conditions
are good for skuas. The wintering areas of the species correspond to sectors of high concentrations
of breeding or wintering tropical, Northern, and Southern Hemisphere seabird species
that are likely to be kleptoparasitized by skuas. A certain degree of individual variation exists
within each population, which induces a spatial overlap in the wintering grounds of distant breeding
populations. These results have potential important consequences in terms of fitness, genetic
divergence, and susceptibility to climate change and marine pollution.