Climate change kills emperor penguins in the Antarctic
over the past 50 years the population of Antarctic emperor penguins has declined by 50 per cent. And, global warming could be to blame. Christophe Barbraud and Henri Weimerskirch, researchers at the French National Centre for Scientific Research in Villers en Bois, France, have shown that an abnormally long warm spell in the southern oceans during the late 1970s could have caused the decline in the population of emperor penguins at the their colony located near Dumont d'Urville Station (66.7 South and 140.0 East) in Terre Adelie, Antarctica. They used the longest series of climate data available, collected between 1952 and 2000, to study the relation between climate change, the survival rates and breeding success of emperor penguins.
The warm spell of the late 1970s was caused by the Antarctic circumpolar wave -- huge masses of warm and cold water that encircle Antarctica once every eight years. As a result of the cycle, Terre Adelie experiences a warming period every four or five years, lasting about one year. In the late 1970s, however, the warming continued for several years. Data from the meteorological station, positioned 500 metres from the penguin colony shows that, after a period of stability in the 1960s (when the decadal average temperatures was -17.3 C ), winter temperatures began to vary extensively and were high throughout the 1970s (decadal average temperature being -14.7 C ). Temperatures again decreased on an average but remained variable.
Weimerskirch thinks the unusually warm spell was probably the result of global warming. Warmer air and rising sea surface temperatures in the Antarctic reduce the amount of ice in the sea. This, in turn reduces the populations of krill, a shrimp-like crustacean, which is the staple diet of the penguins. With less food to eat, emperor penguins die. This has been the cause behind the sharp decline in the penguin population at Terre Adelie. Weimerskirch is reported as saying: "The population decreased because of the low rates of survival over four to five successive years." The survival rate was particularly low in 1972, in 1976-1980 and in 1985. The prolonged period of low survival during the late 1970s corresponds to the period of rapid decline of the breeding population. Changes in the annual breeding population size were related to annual survival and explained 64 per cent of the variation in survival rates. The decline in population during the second half of the 1970s was, the two researchers concluded, caused by this unusually long period of low adult survival. The growth rate of populations of long-lived species is mainly sensitive to changes in survival rates of the adults. High emigration from the colony was ruled out as a cause for the disappearance of penguins as the nearest colony is about 1,000 km away and penguins, like other seabirds, like to stick to one breeding site once they have started to reproduce.
An increase in the sea ice level increases the food available for penguins but the size of the penguins' broods get reduced when sea ice is more extensive. After laying eggs, a female penguin travels, across the ice, out to the waters to feed on krill, fish and squid, which she regurgitates to feed her young. The male keeps the eggs warm until her return. If the sea ice is extensive, the female may be gone for months in search of food. In such a condition the male eventually gives in to his hunger and abandons the egg or chick.
The researchers noted the paradoxical role the extent of ice sea plays in the penguin ecosystem. An increased sea ice-spread provides nutritional advantage. It provides more food for the emperor penguins. Consequently, it increases the survival rates of the animals. But an increase reduces fecundity. But the researchers warn not to jump the gun and generalise about the impacts of climate change on wildlife. For example, a reduction in the amount of sea ice is favorable to Adelie penguins.
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