Wellington - Analysis of ancient penguin guano has revealed that volcanic eruptions, not climate change, almost wiped out an Antarctic sea bird colony three times, researchers have found.There has long been speculation linking fluctuations in penguin populations over recent decades to climate change, but scientists studying a colony of gentoo penguins in Antarctica wanted to look back much further.The team, led by the British Antarctic Survey, hit upon the idea of drilling core samples from ancient guano deposits, giving them a record going back 7 000 years.The results, published in Nature this week, showed the penguins of the Ardley Island colony had been dramatically impacted by a nearby volcano at Deception Island.Lead researcher Steve Roberts said the millennia-old droppings, collected from the bed of a lake on the island, still had an intense smell.But more importantly, the sediment cores also contained clear layers of volcanic ash, while biogeochemical analysis of the droppings provided insights into the colony's population over time."On at least three occasions during the past 7 000 years, the penguin population... was almost completely wiped out locally after each of three large volcanic eruptions," Roberts said."It took, on average, between 400 and 800 years for it to re-establish itself sustainably."The guano analysis found "no consistent relationships" between climate conditions and the penguin population in the Ardley Island colony, which currently has about 5 000 of the birds.British Antarctic Survey penguin ecologist Claire Waluda said the innovative technique could be used to examine how volcanoes had affected other colonies."Changes in penguin populations on the Antarctic peninsula have been linked to climate variability and sea-ice changes, but the potentially devastating long-term impact of volcanic activity has not previously been considered," she said.