Saturday, March 3, 2012

Penguins' food goes south

Posted on: 03 Mar 2012

Climate change warming the sea surface is separating breeding King Penguins from their main food sources, a new study shows.

King Penguins are the top avian fish consumers in the southern oceans, and their feeding ranges, habits and behaviour have been widely studied in this context for decades. However, overall seabird populations in the Antarctic's catchment have been changing for at least the last three decades and demographic modelling suggests that there will be radical changes over the next 100 years. The polar regions have been warming at a  faster rate than more temperate and tropical areas, and most scientific predictions are that this will continue over the rest of the century.

The Crozet Islands' King Penguins number well over one million individuals, far and away the largest population in the world and not currently viewed as being under any conservation threat. The population has been studied fairly comprehensively since the early 1960s and, though the population increased up to the 1990s, since 1994 there has been a notable decline. A particular long-term breeding dataset from Possession Islands in the archipelago was used to understand and model the habitat the penguins use during incubation and brooding, and to predict how the warming of the southern oceans would affect the distribution of this habitat, so important for the penguins continued survival.

The study's data confirmed that sea surface temperature controls the areas that are productive for King Penguin foraging during incubation and brooding, and that the penguins mostly use the colder pelagic waters of the polar air mass front, tracking these as they fluctuate between 300-500 km south of their colony. Models derived from the long-term data predict that the optimum feeding zones will shift south by about 400 km by 2100, and that therefore feeding during the early stages of the breeding cycle will become a significant challenge in the near future.

Clearly, the penguins reliance on the fish species that congregate around the polar front will mean that birds already under pressure from breeding will have to expend more energy swimming further  to collect more food over a shorter time period, a handicap compounded as the front moves gradually southwards over the course of the summer, anyway.

Demographic studies already indicate that breeding success declines during warmer summers in the Crozet Islands, but this may not necessarily be the case at other on Kerguelen and Heard islands, which are not as affected by the warming surface temperatures due to the shallower seas around them reducing the amount of annual temperature variation. Also, not enough is known about the responses of the major fish prey species involved to the changing surface temperatures to fully predict their movements, though fish have certainly changed their distribution in other parts of the world because of this.

However, the 21st century is not looking good for the Crozet Island populations unless they are able to evolve new foraging strategies or move to alternative breeding sites over time.

Péron, C, Weimerskirch, H and Bost, C-A. 2012. Projected poleward shift of king penguins (Aptenodytes patagonicus) foraging range at the Crozet Islands, southern Indian Ocean. Proceedings of the Royal Society B: doi: 10.1098/rspb.2011.2705.

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