The most common bird on St Kilda is the puffin, with roughly 270, 000 birds on the islands in summer. They only come ashore to lay their eggs and look after their young.
Puffins don't nest on cliff edges. Instead they lay their eggs in burrows which they dig in the green, grassy slopes at the top of a cliff. The island of Dun is perfect for them. Here they are protected against predators. When the pufflings hatch in the summer and begin to fly, some of them are attracted to the lights on the buildings. So the St Kilda ranger weighs the birds, puts an identity ring on them and releases them back off the end of the pier.
Puffins only have a bright stripy beak in the summer months. The rest of the year it's a dull yellow colour.
Puffins spend most of their life at sea and are excellent swimmers. They use their wings to fly underwater, like penguins do. They are sometimes called 'Tammie Norries' by people on the islands of Scotland.