Italian photographer Stefano Unterthiner travelled to Lake Tysslingen in Sweden to document the whooper swans which rest there en route to their Arctic breeding grounds. He worked in temperatures as low as -17 degrees C to photograph the swans flying in to roost on the frozen lake.
The whooper swan is one of Europe's conservation success stories. In Sweden the breeding population has increased from 30 to 6000 pairs in the last 30 years. The UK is also a major wintering ground for whooper swans, with more than 6000 birds making the long migration from Iceland. At 10 kilograms, the whooper swan is one of the heaviest migrant birds, and is capable of migrating non-stop for more than 1400km across the sea, from Iceland to Ireland.