When sea‐ice clock is ahead of Adélie penguins’ clock

Abstract

Abstract1. In Polar Regions, the extent and dynamics of sea-ice are changing. This affects the ocean productivity which consecutively impacts plankton communities and polar top predators like penguins. Yet, the underlying behavioural and physiological mechanisms remain poorly understood. 2.Here we monitored the ecophysiological responses of Ade´lie penguin (Pygoscelis adeliae) pairs during two seasons of contrasting timing of sea-ice retreat. Beside classical breeding parameters like foraging trip duration, body mass and reproductive success, we also investigated food-related stress (via plasma corticosterone concentration), nutritional state (via metabolite levels) and the use of penguins' habitat (via blood isotopic values). 3. Body mass and reproductive success remained unchanged but foraging trips were shorter when sea-ice retreated earlier. Constant plasma corticosterone concentrations indicated that none of the feeding conditions resulted in a food-related stress. However metabolite levels were lower when sea-ice retreated early, suggesting that the foraging performance and the quality ⁄ quantity of food differed. Indeed isotopic ratios indicated that coastal prey like fish contributed more to the penguins' diet when sea-ice retreated prematurely. 4. The early sea-ice retreat was related to higher chlorophyll concentrations, known to favour krill recruitment. Paradoxically, this was not associated to a higher krill contribution in the penguins' diet. We propose that a shift in the phytoplankton quality (rather than quantity), affecting krill recruitment, forced penguins to switch to more available prey like coastal fish. 5. In some Antarctic regions, sea-ice is retreating earlier and earlier. In the present study, even though the timing of sea-ice retreat and the consecutive ocean productivity differed drastically between the 2 years, Ade´lie penguins were not severely affected because they were able to adjust their at-sea behaviour and thus maintained their body condition and reproductive success unchanged. 6. This suggests that the timing of sea-ice retreat does not represent an important threat to populations of Ade´lie penguins at least as long as alternative resources are still available and other environmental parameters like winter sea-ice extent are not dramatically altered.

Reproductive consequences of environment-driven variation in Adélie penguin breeding phenology

“…There is concern that phenological changes could lead to a mismatch between periods when penguins must provision their chicks and when they have access to prey (Visser & Both 2005, Forcada & Trathan 2009, Beaulieu et al 2010. At Béchervaise Island, prey is more accessible when the ice breaks out (Clarke et al 2006), usually during the chickrearing period (Fig.…”

Determining Seabird Body Condition Using Nonlethal Measures

“…However, birds may be able to buffer the effects of variable food supplies by altering their foraging effort (Burger and Piatt 1990); such extra energy expenditure should be reflected physiologically. Hence, using an index of energy reserves coupled with an understanding of how lipids are mobilized can provide a sensitive early-detection tool for monitoring the health of marine ecosystems Montevecchi 2007;Beaulieu et al 2009;Burke and Montevecchi 2009;Ropert-Coudert et al 2009). …”

Foraging strategies of Adélie penguins: adjusting body condition to cope with environmental variability

“…Given the choice, Adélie penguins feed in close proximity to sea ice, presumably because their preferred prey is found there, but potentially also because it offers a resting platform and easy source of drinking water (Ainley 2002). When sea ice is far from breeding colonies the penguins' foraging efficiency decreases, foraging effort increases, or both; parents undergo a severe loss in mass, less food is returned to chicks (Ainley et al 1998), and prey type may shift (Ainley et al 2003, Beaulieu et al 2010). Alternatively, if there is insufficient open-water between floes, the presence of too much sea ice can present a physical barrier (Massom et al 2006, Emmerson & Southwell 2008.…”

“…As a major habitat variable affecting penguin foraging and reproductive effort, sea ice coverage and prox-imity is important (Ainley 2002, Clarke et al 2006, Cockrem et al 2006, Emmerson & Southwell 2008, Beaulieu et al 2010. Given the choice, Adélie penguins feed in close proximity to sea ice, presumably because their preferred prey is found there, but potentially also because it offers a resting platform and easy source of drinking water (Ainley 2002).…”