Population-specific wintering distributions of adult south polar skuas over three oceans

Abstract

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 geolocation 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 δ 15 N 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.

Consistent variation in individual migration strategies of brown skuas

“…2 & 3). Individual consistency in migration strategies was also recorded for 17 south polar skuas Catharacta maccormicki and 3 great skuas C. skua tracked in 2 and 3 consecutive nonbreeding seasons (Kopp et al 2011, Magnúsdóttir et al 2012, Weimerskirch et. al.…”

“…Individuals from the southern and northern end of the range ('SouthPata' and 'SouthBrazil' strategies) used the highly productive but seasonal frontal systems of the southern Patagonian Shelf (Acha et al 2004, Rivas et al 2006, and the South Brazil Shelf (Acha et al 2004), respectively. During this period, the tracked individuals spent only a small proportion of the day flying, a pattern found in brown, great and south polar skuas (Phillips et al 2007, Magnúsdóttir et al 2014, Weimerskirch et al 2015, Carneiro et al 2016. A clear diurnal pattern was apparent, with multiple landings during the day, interspersed by 3 to 4 short flight bouts of approximately 1 h. On average, females made longer flight bouts than males and spend less time foraging (Table 1).…”

“…This suggests that they might have been hybrids between brown skuas and the smaller south polar skua, as hybridisation between these closely-related species occurs frequently (Ritz et al 2006). This might explain their distinctive migration pattern, as south polar skuas are trans-equatorial migrants (Kopp et al 2011, Weimerskirch et al 2015, and hybridisation is known to alter migration behaviour in other species (e.g. Helbig 1991).…”

Combination of At-Sea Activity, Geolocation and Feather Stable Isotopes Documents Where and When Seabirds Molt

“…Variations in the intensity, duration and timing of the transient increase in time spent on water can be expected, especially in relationships with different molt patterns and wing-molt durations (Bridge, 2006). Finally, a general critical assessment of activity level in relation to molt is also needed in other seabird groups, because an increase in time spent on water during the inter-breeding period was already found in sulids (Garthe et al, 2012), skuas (Phillips et al, 2007;Magnusdottir et al, 2014;Weimerskirch et al, 2015b), and alcids (Mosbech et al, 2012), thus suggesting that it is potentially a main characteristic of flying seabird energy budget overall.…”

“…DNA was extracted from blood cells and the chromo helicase DNA-binding (CHD) gene was amplified in a polymerase chain reaction procedure (Weimerskirch et al, 2005). A few body feathers that likely grew simultaneously to the GLS tracking were collected from the lower back of birds at recapture.…”