The Atlantic puffin is a colorful seabird and is the only puffin native to the Atlantic Ocean. It has a black crown and back, pale grey cheek patches, and white underparts. Its broad boldly marked red and black beak and orange legs contrast with its plumage. It molts while at sea in the winter and some of the bright-colored facial characteristics are lost, with color returning again during the spring. The juvenile has similar plumage, but its cheek patches are dark grey. The juvenile does not have brightly colored head ornamentation, its bill is narrower and is dark-grey with a yellowish-brown tip, and its legs and feet are also dark. Puffins from northern populations are typically larger than in the south and these populations are generally considered a different subspecies.
Atlantic puffins are birds of the colder waters of the North Atlantic Ocean. They breed on the coasts of northwest Europe, the Arctic fringes, and eastern North America. While at sea, puffins range widely across the North Atlantic Ocean, including the North Sea, and may enter the Arctic Circle. In the summer, their southern limit stretches from northern France to Maine and in the winter, the birds may range as far south as the Mediterranean Sea and North Carolina. Atlantic puffins spend autumn and winter out in the open ocean and breed on grassy coastal slopes and rocky cliffs.
Atlantic puffins spend most of the year far from land in the open ocean and only visit coastal areas to breed. They are sociable birds and they usually breed in large colonies. However, when out at sea, they prefer to stay solitary and bob about like a cork, propelling themselves through the water with powerful thrusts of their feet. When fishing, puffins swim underwater using their wings as paddles to "fly" through the water and their feet as a rudder. They swim fast and can reach considerable depths and stay submerged for up to a minute. They fish by sight and can swallow small fish while submerged, but larger specimens are brought to the surface. In the spring, mature birds return to land, usually to the colony where they were hatched. Each large puffin colony is divided into subcolonies by physical boundaries such as stands of bracken or gorse. On the ground, they spend much time preening, spreading oil from their preen gland, and setting each feather in its correct position with beak or claw. They also spend time standing by their burrow entrances and interacting with passing birds. The colony is most active in the evening, with birds standing outside their burrows, resting on the turf, or strolling around. Then, the slopes empty for the night as puffins fly out to sea to roost, often choosing to do so at fishing grounds ready for early-morning fishing.
Atlantic puffins are monogamous and mate for life. The male spends more time guarding and maintaining the nest, while the female is more involved in incubation and feeding the chick. Upon returning to breeding grounds Atlantic puffins soon start to excavate burrows on grassy clifftops or may reuse existing holes, and on occasion may nest in crevices and among rocks and scree. Often, one stands outside the entrance while the other excavates, kicking out quantities of soil and grit. Apart from nest-building, the other way in which the birds restore their bond is by billing; the pair approaches each other, each wagging their heads from side to side, and then rattling their beaks together. Egg-laying starts in April in more southerly colonies but seldom occurs before June in Greenland. The female lays a single white egg and both parents incubate it about 39-45 days. The first evidence that hatching has taken place is the arrival of an adult with a beak-load of fish. The chick is covered in fluffy black down and its eyes are open and it can stand as soon as it is hatched. The chick sleeps much of the time and also moves around the burrow rearranging nesting material, picks up and drops small stones, flaps its immature wings, and pulls at protruding root ends. The chick takes from 34 to 50 days to fledge and usually leaves the nest for the first time at night when the risk of predation is at its lowest. When the moment arrives, it emerges from the burrow and walks, runs, and flaps its way to the sea. When it reaches the water, it paddles out to sea and may be 3 km (2 mi) away from the shore by daybreak. It does not congregate with other puffins and does not return to land for 2-3 years. At the age of 4-5 years, it will become reproductively mature and will be able to breed.
The main causes of the Atlantic puffin population decline are due to increased predation by gulls and skuas, the introduction of rats, cats, dogs, and foxes onto some islands used for nesting, contamination by toxic residues, drowning in fishing nets, declining food supplies, hunting, and climate change. Since puffins spend winters on the open ocean, they are susceptible to human actions and catastrophes such as oil spills. Oiled plumage makes birds more vulnerable to temperature fluctuations and less buoyant in the water. Many birds die, and others, while attempting to remove the oil by preening, ingest and inhale toxins. Puffins have been also hunted by man since time immemorial. They were caught and eaten fresh, salted in brine, or smoked and dried. Their feathers were used in bedding and their eggs were eaten. Even at present, these beautiful birds are still caught and eaten in Iceland and the Faroe Islands. Changes in climate also affect populations of the Atlantic puffin. In Maine, shifting fish populations due to changes in sea temperature causes the lack of availability of the herring, which is the staple diet of the puffins in the area. As a result, some adult birds become emaciated and die and chicks die from starvation.
According to the IUCN Red List, the global population size of the Atlantic puffin is 12-14 million mature individuals. The European population consists of 4,770,000-5,780,000 pairs, which equates to 9,550,000-11,600,000 mature individuals. Currently, this species is classified as Vulnerable (VU) on the IUCN Red List and its numbers today are decreasing.