Morus bassanus (Linnaeus, 1758)

Taxonomy and Basic Classification

The northern gannet, with the scientific name Morus bassanus (Linnaeus, 1758), is the largest gannet species and the largest seabird native to the western Palearctic.

Adult Size Measurements

Adult northern gannets measure 87–100 cm (34+1⁄2–39+1⁄2 in) in length, have a 170–180 cm (67–71 in) wingspan, and weigh 2.3–3.6 kg (5–8 lb). Males and females are generally similar in size and appearance.

Adult Plumage and Coloration

Their plumage is white with dark brown to black wing tips; the primary flight feathers, primary coverts, and alulae are all dark. The head and neck have a buff-yellow tint that grows much more prominent during the breeding season, and males have deeper colouring than females.

Facial and Eye Features

A ring of black bare skin surrounds the eyes, which also feature a cobalt blue orbital ring. The iris is light blue-grey with a fine dark outer ring, though irises turn black in birds that survive avian influenza.

Beak Structure and Coloration

The beak is long, strong, and conical, with a slight downward curve at the tip and a sharp cutting edge. Adult beaks are blue-grey with dark grey or black edges.

Mandible and Facial Markings

A black groove runs the full length of the mandible, and merges into the skin around the eyes. A black band of bare skin separates the pale feathers of the forehead and throat from the bill, forming the species' distinctive face marking.

Foot Structure and Coloration

All four toes on the feet are connected by webbing, which ranges in colour from dark grey to dark brown. Coloured lines run along the toes and continue up the legs: these lines are typically greenish-yellow in males and bluish in females, and are thought to play a role in mating.

Fledgling Plumage

Fledgling northern gannets are dark grey to slate-grey, with fine white speckling on their upperparts and wings. They have a prominent V-shaped white area under the rump, dark brown-black wing tips and tail with partial white tipping, and dark brown bills and irises.

Fledgling Development

Fledglings can weigh more than 4 kg (9 lb) when they leave the nest at around 10 weeks old. In their second year, their appearance changes based on different moulting phases, and they may have adult-style plumage on the front of their body while remaining brown on the rear.

Maturation Timeline

Gannets gradually grow more white plumage each season after that, and do not reach full maturity until they are five years old.

Comparison with Related Gannet Species

Compared to Cape gannets and Australian gannets, northern gannets are slightly larger, have thicker bills, have more white plumage on their wings, and have an all-white tail, while the other two species have black-tipped tail feathers.

Similarity to Masked Boobies

Northern gannets found along the west coast of Africa could be mistaken for vagrant masked boobies, but masked boobies are smaller overall, have no buff tint on the head, and have a black tail.

Similarity to Albatrosses

From a distance or in poor visibility, albatrosses can be confused with northern gannets, especially immature northern gannets that have more black colouring on the wings.

Breeding Range

The breeding range of the northern gannet spans both sides of the North Atlantic, on coasts influenced by the Gulf Stream. Colonies exist in the Gulf of Saint Lawrence and on islands off the east coast of Canada.

Nesting Habitat

They normally nest in large colonies, on cliffs that overlook the ocean or on small rocky islands.

Habitat Prey Requirements

The water in their habitat must be cool enough to support Atlantic mackerel and herring, the northern gannet's main food source, and these habitats lie over the continental shelf.

Cold Region Survival Adaptations

Northern gannet colonies can exist in the far north in very cold, stormy regions. Researcher Nelson has suggested multiple reasons the species can survive in these regions: their combination of body weight and a powerful beak allows them to catch strong muscular fish, they can dive to great depths to capture prey far from nesting cliffs, their fat reserves act as added weight during diving and serve as energy stores during extended periods without food.

Northern Breeding Range Limit

The northern limit of their breeding range depends on the presence of sea ice-free water during the breeding season. Even though Greenland and Svalbard have otherwise suitable breeding sites, Arctic regions there have summers too short to support the full 26 to 30 week period northern gannets need to lay eggs and raise their young.

Southern Distribution Limit

The southern limit of their distribution depends mainly on the presence of enough prey.

Fossil Evidence

Fossil evidence shows that northern gannets bred on Crete during the Pleistocene.