Eider ducks live on the sea. They float on cold waves all day, diving underwater to find mussels, crabs and small shellfish. They are excellent divers and can hold their breath for over a minute. They swallow mussels whole and their strong stomachs crush the shells inside.
The reason eiders can sit on freezing cold sea water without getting cold is their amazing chest feathers - 'eiderdown'. Eiderdown is so warm and light that for hundreds of years it has been used by people to make duvets and warm jackets for explorers going to the Arctic. One pillow's worth of eiderdown can keep a grown-up warm in deep snow.
When the mother eider makes her nest on the ground, she plucks the down from her own chest to line it - keeping her eggs and babies warm. After the babies leave the nest, people in some Arctic countries carefully gather the leftover down. The mother is not harmed - it is like collecting wool from a sheep.
Baby eider ducklings have a special trick. Once they hatch, many mothers' babies group together into one giant playgroup called a 'cr猫che', with a few aunties watching the lot. Sometimes 50 fluffy chicks paddle behind just two grown-ups. Safety in numbers.