Antarctic petrels 'on the ice rocks': wintering strategy of an Antarctic seabird.

K Delord,A Kato,Y Ropert-Coudert,Y Cherel,C Cotté,S Descamps,A Tarroux,F Orgeret

doi:10.1098/rsos.191429

Abstract

There is a paucity of information on the foraging ecology, especially individual use of sea-ice features and icebergs, over the non-breeding season in many seabird species. Using geolocators and stable isotopes, we defined the movements, distribution and diet of adult Antarctic petrels Thalassoica antarctica from the largest known breeding colony, the inland Svarthamaren, Antarctica. More specifically, we examined how sea-ice concentration and free-drifting icebergs affect the distribution of Antarctic petrels. After breeding, birds moved north to the marginal ice zone (MIZ) in the Weddell sector of the Southern Ocean, following its northward extension during freeze-up in April, and they wintered there in April–August. There, the birds stayed predominantly out of the water (60–80% of the time) suggesting they use icebergs as platforms to stand on and/or to rest. Feather δ15N values encompassed one full trophic level, indicating that birds fed on various proportions of crustaceans and fish/squid, most likely Antarctic krill Euphausia superba and the myctophid fish Electrona antarctica and/or the squid Psychroteuthis glacialis. Birds showed strong affinity for the open waters of the northern boundary of the MIZ, an important iceberg transit area, which offers roosting opportunities and rich prey fields. The strong association of Antarctic petrels with sea-ice cycle and icebergs suggests the species can serve, year-round, as a sentinel of environmental changes for this remote region.

Highlights

Unlike the Arctic and its constantly decreasing sea-ice extent, Antarctica experienced contrasting trends over the last three decades, with record maximum and minimum sea-ice extent within a few years [1,2,3]
Antarctic petrels always preferred ‘openwater’ zones, where SIC is less than 15%, and the probability of presence of the birds was above 0.5 when small icebergs were present and significantly increased with iceberg sizes, especially in June
We show that this tight link with sea ice extends throughout the non-breeding period, with birds tracking the phenology of the sea-ice advance foraging primarily in open waters associated with icebergs

Summary

Introduction

Unlike the Arctic and its constantly decreasing sea-ice extent, Antarctica experienced contrasting trends over the last three decades, with record maximum and minimum sea-ice extent within a few years [1,2,3]. Any change in the icescape may have immediate consequences for petrel demography [21] and probably for their survival rate, as has been shown in other seabird species [22] In this context, the non-breeding season, spanning several months of the austral winter, may constitute a critical period affecting population dynamics through an effect on individual survival [23]. Understanding how changes in the cryosphere during the non-breeding season affect vital rates is important, especially because of a general paucity of biological information during the winter months for Antarctic species. Using 2 years of individual, longitudinal tracking data and stable isotopes, we examined the foraging ecology of Antarctic petrels over the non-breeding season and investigated how physical factors, mainly the sea-ice and icebergs affect birds distribution during this period

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Discussion

Conclusion