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Abstract
Observed large-scale changes in climate and oceanography, which are especially pronounced in the Arctic, represent profound challenges for upper trophic predators. Knowledge about the extent to which marine predators are able to adjust to environmental variability is essential in order to assess the impact of changing oceanic conditions on the Arctic ecosystem. The main goal of this study was to investigate the impact of oceanographic conditions that varied on an inter-annual and inter-colony basis on the foraging and breeding strategy of a zooplanktivorous alcid, the little auk Alle alle. The study was conducted in two little auk breeding colonies in Spitsbergen (Hornsund and Magdalenefjord) located in different hydrographical regimes in two contrasting seasons (2009 and 2010). This article provides a comprehensive study linking a number of variables describing foraging ground quality, measured directly at sea, with the birds' foraging strategy, parental efforts, body condition and survival of nestlings. The analyses revealed that under conditions of high water temperature and a low proportion of the preferred food item, Calanus glacialis, in relation to less energetically profitable Calanus finmarchicus in the little auks' foraging grounds, birds increased the overall duration of their foraging trips and decreased the frequency of chick feeding. The resulting lower calorific value of food delivered daily to the chicks entailed reduced chick survival. We might expect that further ocean warming would impair the time and energy budget of parent birds and, in consequence, the breeding success of the little auks.
Acknowledgements
We would like to thank Mateusz Barcikowski, Lech Iliszko, Adam Nawrot, Jan Samolyk, Gosia Jakimiak and Wojtek Iliszko for their help with the fieldwork. Thanks to Mateusz Barcikowski for his advice in the statistical analyses. We appreciate the improvements in English usage made by Phil Whitford through the Association of Field Ornithologists' programme of editorial assistance. The study was conducted with the permission of the Governor of Svalbard and the Norwegian Animal Research Authority. We thank the captain and crew of the R/V Oceania of the Institute of Oceanology, Polish Academy of Sciences and the Polish Polar Station of the Institute of Geophysics, Polish Academy of Science for their support with logistics.
Editorial responsibility: Leandro Bugoni
