Parental efforts of an Arctic seabird, the little auk Alle alle, under variable foraging conditions

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.