Atlantic puffins are birds that live at sea most of their lives. They fly through the air like most birds, but they also "fly" through the water, using their wings as paddles. As they swim, they use their webbed feet to steer, much as a boat uses a rudder. Puffins eat small fish￢ﾀﾔsuch as sand eels and herring￢ﾀﾔwhich they hunt underwater. They generally stay underwater for 30 seconds or less, but are able to stay down for up to a minute and dive 200 feet (61 meters) deep. Well adapted for their home in the water, puffins are also speedy in the air. They flap their wings up to 400 times a minute, speeding along in the air at 55 miles (88 kilometers) an hour. In the spring and summer, thousands of puffins gather in colonies on the coasts and islands of the North Atlantic Ocean. Pairs of puffins often become mates for life, finding each other at their breeding colony year after year. The pair often uses the same burrow they used the year before. Puffin nesting sites are often on steep, rocky cliffs, where the birds and their eggs are safer from predators. The birds nest in burrows in the ground or in a sheltered area among rocks. To dig a burrow, male and female puffins use their beaks to cut into the dirt and then, like dogs, use their feet to move the dirt out behind them. A burrow is about three feet (91 centimetres) long. The birds line their nest, located at the end of the burrow, with grasses, seaweed, and feathers. Both parents take care of the single egg the female lays. It takes about 42 days to hatch. Mom and dad both care for the hatchling, too, feeding their chick with small fish that they carry back to the nest from the sea. When puffins are just feeding themselves, they tend to swallow the fish they catch while still underwater. When they are feeding their young, they generally carry several small fish at a time back to the nest for their youngster. Using their round tongues, the birds push the fish upward into small notches in their upper bill that help hold the food securely. That way, the puffin can keep its mouth open to catch more fish, adding to the collection already in the back part of its mouth. Once a puffin hatches, it takes about 49 days for it to learn to fly and be able to live on its own. The young puffins leave their nest for good at this point, when they fly or swim out to sea.