A volcanic eruption on a small sub Antarctic island is depositing ash over one of the world's largest penguin colonies, prompting concern among scientists and conservationists.

Zavodovski Island, the most northerly of a 290-mile arc of 11 islets near South Georgia called the South Sandwich Islands, has been called the "smelliest place on Earth" because of the sulfuric air emitted by the volcano, Mt. Curry. Its landmarks carry such names as Noxious Bluff and Stench Point. That, however, seems to be of little concern to the island's colony of chinstrap penguins, which numbers more than 1 million strong, the largest colony of that species and one of the largest penguin colonies in the world.

In March, the region was rocked by a 7.2 magnitude earthquake, and satellite imagery subsequently showed that Mt. Curry and a nearby volcano, Mt. Sourabaya on Bristol Island to the south, were erupting. Fishing vessels in the area captured images of the Mt. Zavadovski eruption, which showed that the prevailing wind is depositing most of the smoke and ash on the lower slopes of the volcano. This is where the chinstraps, closely packed in huge numbers, make their home -- as do around 180,000 macaroni penguins.

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Satellite images have confirmed that between one third and one half of the island has so far been covered in ash. At the time photos were taken, the adult chinstraps were molting, shedding their old feathers for new ones and therefore unable to leave the island and enter the water to wash off the ash.

In a press release, British Antarctic Survey geographer Peter Fretwell said that, "We don't know what impact the ash will have on the penguins. If it has been heavy and widespread it may have a serious effect on the population. It's impossible to say but two scientific expeditions are scheduled to visit the region from later this year and will try to assess the impact of the eruption."

Meanwhile, researchers have found that king penguins, another species found on sub Antarctic islands, can distinguish between dangerous and benign sounds, even when asleep.

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According to Tessa Abigail van Walsum of the University of Roehampton in England, playing king penguins "the calls of orcas or skuas caused them to wake up and flee," whereas single tones elicited no response.

Penguins also had strong reactions to some non-predator sounds, such as of approaching elephant seals, which could easily crush any sleeping penguins in their way. Notably, playing them the sound of unfamiliar predators, such as a dog's growl, got little reaction when they awoke.

The ability of these birds to respond differently upon waking up suggests that they might sleep with just one half of their brain, while keeping close watch with the other half, an important adaptation for birds that return exhausted from long diving expeditions.

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