King penguin chicks have been filmed bathing in a \"mud spa\". The birds use streams and thick, cooling mud to keep their large, fluffy bodies from overheating in summer temperatures that can reach 17C. A BBC film crew captured the behaviour in St Andrews Bay, South Georgia, whilst filming for the documentary Frozen Planet. The team set out to capture footage of chicks paddling in rivers and streams; the mud-bathing was \"unexpected\". \"I don\'t think it\'s been filmed before,\" programme producer Miles Barton told BBC Nature. And his colleagues spent a week with the bay\'s penguin colony, documenting the behaviour of the birds. \"These big fluffy chicks are on a 10-month cycle,\" Mr Barton explained. \"They have to be able to survive the winter and the summer.\" Their thick downy coats protect them in winter temperatures on the sub-Antarctic island, which can fall to about -10C. But when the team arrived on the island in early November, they found penguin chicks lined up around the streams, apparently wanting to cool off in the mild summer sunshine. \"The streams run off the glacier, so the water\'s nice and chilly for them,\" said Mr Barton. \"But the problem is that their coats aren\'t designed for swimming. Penguins on South Georgia The king penguin colony on St Andrews Bay - beautiful but very smelly \"So we\'d see one of them suddenly launch itself into the water, then leap up again almost immediately as if it was shocked to find itself in this alien element.\" Occasionally though, a penguin would immerse itself and swim around much like the adult birds do. \"But when the chicks got wet, they looked liked drowned rats,\" Mr Barton recalled. He said that there was a serious and rather risky side to this comic cooling behaviour. If penguin chicks are caught in a strong current, they can be swept out to sea and large predatory seabirds, giant petrels, wait at the mouth of the stream to \"pick off\" any weak, struggling penguins. Foul spa A safer and more comical method of cooling down that a few of the chicks were enticed by, was a dark, muddy pool. They appeared to use this as a spa. \"What you don\'t want to know is what was in that pool,\" said Mr Barton. The island, he explained, is home to 400,000 penguins, so the beaches are covered with penguin waste and the remains - beaks, feathers, scales and bones - of dead birds. \"That pool was the rotted remains of dead penguins and tonnes of penguin poo,\" said Mr Barton. He recalled that the scenery and the penguin colony were beautiful, but that, like all penguin colonies, it \"absolutely stank\". \"It smells like a combination of rotting fish and the sea,\" he explained. \"But you kind of get used to it on the first day.\"