Throughout the year, the diet consists mainly of various species of fish, particularly sand eels. Puffins dive beneath the surface of the water and swim using their wings, in pursuit of prey (3). If they are feeding their young, they fill their bill with fish and carry them back to the burrow (3). For most of the year, puffins are out at sea, they return to land in order to breed. Just before the breeding season, the annual moult occurs; birds are flightless for a time after moulting, but they are still able to swim underwater, and can return to the breeding colonies between February and early April (4). Upon their return, comical displays can ensue, including bill-knocking and ritualised walking around the burrow entrance (3). New burrows may be made, or old ones utilised. A single egg is laid in a chamber at the end of the burrow in May. After an incubation period of up to 43 days, the chick hatches and remains inside the burrow for 6 weeks or so, after which time it becomes fully independent, dispersing out to sea (3).