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Seabirds in seasonal environments are often long-distance migrants and, for many species and populations, their ranges throughout the non-breeding period are unknown. As conditions during the non-breeding season often affect subsequent performance, the choice of migration strategy can have major implications for timing of breeding and success and, ultimately, population dynamics. We tracked south polar skuas Catharacta maccormicki from a single breeding population at King George Island in the South Shetland Islands (Antarctica). Overall, 27 birds (69%) migrated to the northern Atlantic (3 regions), 10 birds (26%) to the northern Pacific Ocean (2 regions), and 2 birds wintered in the southern hemisphere. Individuals tracked in consecutive non-breeding seasons chose the same ocean for wintering. Despite migrating to different oceans, birds showed a similar figure-ofeight flight pattern and equivalent residency periods in the main wintering areas. In addition, 87% of the migrants used terminal stop-over sites off South America shortly before returning to the breeding site. High diversity of migration patterns may buffer south polar skuas from climate change and other anthropogenic threats.KEY WORDS: Migratory connectivity · Annual cycle · Seabird · Antarctic · Pacific · Trans-equatorial · Geolocator Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 435: [263][264][265][266][267] 2011 & Larsson 1997). However, in the absence of tracking data, there were no studies of the routes or wintering destinations used by specific breeding populations. The purpose of this study was to determine intrapopulation variability in migration patterns of south polar skuas breeding on King George Island, which might theoretically overwinter in either the Pacific or Atlantic oceans. MATERIALS AND METHODSWe equipped 58 adult south polar skuas (27 females, 29 males, 2 unknown sex) with light recording geolocators (British Antarctic Survey, Cambridge) during 3 breeding seasons (2006)(2007)(2008) at King George Island in the Maritime Antarctic (62°12' S, 58°58' W). The geo locators (MK5 and MK9) weighed 9.4 and 8.2 g including the steel ring, respectively, which corresponded to ca. 0.8% of the mean adult body mass. Thirty-nine individuals (18 females, 20 males, 1 unknown sex; all birds were later genetically sexed, Fridolfs son & Ellegren 1999) were recaptured at the same breeding site during consecutive seasons until 2010, resulting in 52 annual tracks. Re-sighting rate did not differ between equipped birds (83%) and breeding birds without a device (78%, logistic regression, Wald = 7.28, p = 0.393). Two positions per day were calculated from light measurements using TransEdit and BirdTracker software (British Antarctic Survey, Cambridge), based on a standard approach (Phillips et al. 2006). Positions that were derived from interrupted light curves around dawn or dusk, that were close to equinoxes, or were obviously erroneous, were excluded, resulting in an average of 331 ± 25 valid...

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a b s t r a c tWhilst we have now a good understanding how past glaciation influenced species at the northern hemisphere, our knowledge of patterns and modes of speciation is far more limited for the southern hemisphere. We provide mtDNA based data on the phylogeography of a circumpolar distributed southern hemisphere seabird group-the southern skua complex (Catharacta spp.). Diversification of southern skuas dates between 210,000 yBP and 150,000 yBP and coincides with a glacial spanning 230,000-140,000 yBP. Skuas most likely first inhabited the Antarctic continent, in the course of global cooling and increasing glaciation spread to the sub-antarctic islands and Tristan da Cunha and finally colonized Patagonia and the Falkland Islands at the glacial maximum. Despite significant differences between taxa most populations still exchange genes with neighboring populations of other taxa and speciation is incomplete.

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