|Emperor penguins. Photo by StormPetrel1.|
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Where they went is a mystery. Lead author Phil Trathan from British Antarctic Survey said, "It is not clear whether the colony died out or relocated. Emperor penguins are thought to return each year to the sites where they hatched, but the colonies must sometimes relocate because of changes in the sea ice."
As to why, it looks like the effects of climate change have struck again. The colony's disappearance has been attributed to a reduction in sea ice, which the emperors need for breeding and foraging.
The colony was found in 1948 when scientists observed 150 breeding pairs gathering on the island. The number of penguins in the colony has been declining steadily since 1970, and in 2009 a high resolution aerial survey showed no trace of the colony. This decline in numbers relates closely to a rise in local air temperature and seasonal changes in ice duration, which are associated with - you guessed it - climate change.
"It is clear that emperor penguins are vulnerable to changes in sea ice and the one site in Antarctica where we have seen really big changes in ice is the West Antarctic Peninsula. For much of the 20th century, this region has warmed at an unprecedented rate, particularly in recent decades," said Dr Trathan.
He added, "Continued climate change is likely to impact on future breeding success."
The paper also looked at alternative reasons behind the colony's disappearance. The authors discounted competition from fisheries and the impacts of tourism, and said there was no data to support the ideas that disease or unusual weather conditions were responsible. However, they stressed the need for similar studies elsewhere in the Antarctic to reduce uncertainty about risks to emperor penguins.
First recorded loss of an emperor penguin colony, 10 March 2011, British Antarctic Survey
PLoS One citation
First recorded loss of an emperor penguin colony in the recent period of Antarctic regional warming: implications for other colonies. Trathan P.N., Fretwell P.T., Stonehouse B. PLoS One 6(2). 28 February 2011.