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"The trigger for the decline was a particularly warm spell in the 1970s"
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Thursday, 10 May, 2001, 05:37 GMT 06:37 UK
'Heatwave' stresses penguins
Penguin BBC Wild
Emperor penguin numbers have now stabilised
French scientists have warned that penguins in the Antarctic could be very susceptible to changes in climate and could be threatened by any long-term temperature shifts.

The researchers made their remarks after observing a dramatic decline in the population of one bird colony, which coincided with an abnormal warm period in the Southern Ocean in the 1970s.

The penguin numbers at Dumont d'Urville Station in Terre Adelie were found to have dropped abruptly by 50% when the average winter temperatures in the area rose from minus 17.3C to minus 14.7C.

However, British researchers cautioned against jumping to conclusions about any global warming and insisted that overall penguin numbers in the Antarctic were healthy.

Egg hatching

The temperature increase at Terre Adelie, which lasted into the early 1980s, raised sea-surface temperatures and reduced the extent of local sea ice.

Reduced sea ice is associated with a lower abundance of krill, the small shrimps that are a key element of a penguin's diet along with fish and squid.

Christophe Barbraud and Henri Wirmerskirch, from the Centre d'Etudes Biologiques de Chize, in Villiers en Bois, wrote of their findings in the journal Nature: "In years with high SSTs (sea surface temperatures) emperor penguins probably have difficulties in finding food, which could increase mortality."

Paradoxically, extensive winter pack ice reduced egg-hatching success by increasing the distance between the hatching areas and the hunting grounds, the scientists found. This meant, the researchers said, the penguin population faced a trade-off between finding enough food to survive and laying enough eggs to sustain the colony.

Computer models

The researchers report that penguin numbers at Terre Adelie have now stabilised. However, they write in Nature: "Our results...indicate that emperor penguins may be very susceptible to environmental variability."

Commenting on the work, British researchers said the Terre Adelie experience might not have wider implications - particularly with respect to any global warming process that could be taking place.

"The climate models give no clear indication of whether a global warming would mean more or less sea ice in future and how this might affect penguins," Keith Reid, of the BioSciences Division at the British Antarctic Survey, told the BBC "At the moment, there are no indications that the penguin is in trouble."

He added: "It looks like this could be a very localised effect just in this colony. A glacier in that area used to give protection to the colony but the front of it fell off in the 1970s and there were predictions then that the penguin population might go into decline. It's what you'd expected if it's less sheltered there."

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