Northern gannet

The northern gannet (Morus bassanus) is a seabird, the largest species of the gannet family, Sulidae. It is native to the coasts of the Atlantic Ocean, breeding in Western Europe and Northeastern North America. It is the largest seabird in the northern Atlantic. The sexes are similar in appearance. The adult northern gannet has a mainly white streamlined body with a long neck, and long and slender wings. It is 87–100 cm (34+1⁄2–39+1⁄2 in) long with a 170–180 cm (67–71 in) wingspan. The head and nape have a buff tinge that is more prominent in breeding season, and the wings are edged with dark brown-black feathers. The long, pointed bill is blue-grey, contrasting with black, bare skin around the mouth and eyes. Juveniles are mostly grey-brown, becoming increasingly white in the five years it takes them to reach maturity.

Nesting takes place in colonies on both sides of the North Atlantic, the largest of which are at Bass Rock (75,000 pairs as of 2014), St. Kilda (60,000 pairs as of 2013) and Ailsa Craig (33,000 pairs as of 2014) in Scotland, in Ireland (Sceilg Bheag; little Skellig, 35,000 pairs in 2011), Grassholm in Wales, and Bonaventure Island (60,000 pairs in 2009) off the coast of Quebec. Its breeding range has extended northward and eastward, with colonies being established on Russia's Kola Peninsula in 1995 and Bear Island (the southernmost island of Svalbard), in 2011. Colonies are mostly located on offshore islands with cliffs, from which the birds can more easily launch into the air. The northern gannet undertakes seasonal migrations and catches fish (which are the mainstay of its diet) by making high-speed dives into the sea.

The northern gannet was previously hunted for food in certain parts of its range, and although that practice still continues in the Outer Hebrides of Scotland and the Faroe Islands, the bird faces few other natural or man-made threats. Since its population is growing, the International Union for Conservation of Nature considers it a least-concern species. Because it is both a conspicuous and a common bird, it is referred to in several ancient myths and legends.

An adult northern gannet has a 170–180 cm (67–71 in) wingspan, and is 87–100 cm (34+1⁄2–39+1⁄2 in) long and weighs 2.3–3.6 kg (5–8 lb), making it the largest gannet and the largest seabird native to the western Palearctic. The two sexes are generally of a similar size and appearance. The plumage is white with dark brown to black wing tips; the primary flight feathers, primary coverts and alulae are dark. The head and neck are tinged buff-yellow, becoming much more prominent in the breeding season. Males are more deeply coloured than females. The eyes are surrounded by black bare skin and have a cobalt blue orbital ring, the iris is light blue-grey with a fine dark outer ring. In birds that survive avian influenza, the irises become black.

The beak is long, strong and conical with a slight downcurve at the end and a sharp cutting edge. In adults, the beak is blue-grey with dark grey or black edges. There is a black groove running the length of the mandible that merges into the skin around the eyes. A black band of bare skin also separates the pale feathers of the forehead and throat from the bill, which gives the gannet its distinctive face markings. The four-toed feet are joined by a membrane that can vary in colour from dark grey to dark brown. There are coloured lines running along the toes that continue along up the legs. These are typically greenish-yellow in males and bluish in females and probably have a role in mating.

Fledglings are dark grey to slate-grey with upperparts and wings finely speckled with white. There is a prominent V-shaped white area under the rump. The wing tips and tail are dark brown-black, partly tipped with white. The bill and iris are dark brown. They can weigh more than 4 kg (9 lb) by the time they leave the nest at about 10 weeks of age. In the second year, the bird's appearance changes depending on the different phases of moulting: they can have adult plumage at the front and continue to be brown at the rear. Gannets gradually acquire more white in subsequent seasons until they reach maturity after five years.

Northern gannets are slightly larger and thicker-billed than Cape or Australian gannets. The northern gannet has more white in the wings and an all-white tail, the other species having black tips to their tail feathers. Individuals on the west coast of Africa could be confused with vagrant masked boobies, though the latter is smaller overall, lacks the buff tinge to the head, and has a black tail. From a distance, or in poor visibility, albatrosses can be confused with northern gannets, particularly those with immature plumage that have more black on the wings.

Northern gannets have streamlined bodies adapted for plunge-diving at high speed, including powerful neck muscles, and a spongy bone plate at the base of the bill. The nostrils are inside the bill and can be closed to prevent water entry; the eyes are protected by strong nictitating membranes. There are subcutaneous air sacs in the lower body and along the sides. Other air sacs are located between the sternum and the pectoral muscles and between the ribs and the intercostal muscles. These sacs are connected to the lungs and are filled with air when the bird breathes in. The air can be returned to the lungs by muscle contractions.

The feathers are waterproof, which allows the birds to spend long periods in water. A water-impermeable secretion produced by a sebaceous gland covers the feathers and the birds spread it across their body using their beak or head. Individuals have a subcutaneous fat layer, dense down feathers and tightly overlapping feathers that help them withstand low temperatures. A reduced blood flow in the webbing on their feet outside of the breeding season also helps to maintain body temperature when the birds swim.

The northern gannet is a loud and vocal bird, particularly in the colony. Its typical call is a harsh arrah-arrah or urrah-urrah, which is emitted upon arriving or when challenging other gannets at the colony. The call is shortened to a rah rah when fishing or collecting nesting material, and lengthened to a ooo-ah when taking off. The calls of the sexes are similar. According to Nelson northern gannets can recognize the call of their breeding partner, their chicks and birds in neighbouring nests. Individuals from outside this sphere are treated with more aggression.