Northern Gannet (Morus bassanus)

The term ‘gannet’ has become synonymous with greed, a reference to this bird’s gluttony. It dives into the water after fish, swallowing its catch whole even before it reaches the surface.

Description

The northern gannet is a big seabird, measuring 95 cm in length- the size of a large goose. It is all white except for its primary feathers, which are black, giving the impression that its wings have been dipped to the elbow in black ink. Its long, robust bill is pale blue-grey, with a base that starts behind the eye. Adult gannets in the breeding season have a yellowish tinge to their heads and the back of their necks. Juveniles are initially all brown, gradually acquiring their white adult plumage over the course of 4-5 years. Gannets have a distinctive, ‘pointed at both ends’ body shape, and their long, broad wings, long neck and bill, and long, pointed tail form a large cross-shape in flight. Their call is a low, barking ‘arrah!’

Distribution

Gannets occur on both sides of the North Atlantic, in Europe as well as in Canada. There are 6 breeding colonies, or gannetries, in Newfoundland and the Gulf of St. Lawrence, the largest of which is located at Bonaventure Island, Quebec, and is home to at least 48,000 birds. In the winter, Canadian gannets move south along the Atlantic coast as far as Texas.

Ecology

Northern gannets breed in huge colonies on high cliffs overlooking the ocean, where the thousands of white birds swooping around the rock face resemble a whirling snowstorm. It is an excellent, powerful flyer, with a 2 m wingspan that allows it to fly over long distances or to soar effortlessly over the surface of the water, catching the updraft off the peak of each wave. In spite of this airborne mastery, however, gannets are ungainly on land, stepping clumsily between closely-spaced nests and warding off attacks by jealous neighbours as they make their way to their own territories.

This bird has a unique feeding strategy. While many seabirds swim on the surface of the water and then dive under to pursue their prey, the northern gannet flies high in the air, carefully searching for fish underwater, and then dives straight down from heights of up to 30 metres- three times the height of a high diving platform! The impact of hitting the water sends jets of spray as high as 3 metres. Its speed propels it well below the surface, where it may actually come up below its prey- that it pursues by swimming with its large, webbed feet. It usually swallows its catch whole before resurfacing. The gannet is particularly well adapted for this high-diving lifestyle. Just before diving, it inflates special air cells under its skin, which cushion it from the impact of hitting the water. It has no external nostril openings, and the two halves of its bill fit together tightly, so that no water gets into its nose or mouth. The base of its bill is reinforced with thick plates that also protect its head from the impact with the water. In order to judge how far beneath the surface its prey are swimming, this bird has binocular vision- like the terrestrial birds of prey, its eyes are located on the front of its head, giving it 3-D vision and enabling it to pinpoint its target accurately.

Northern gannets are monogamous. A young male gannet selects a nest site and performs head-shaking displays to attract a mate. In their first season, birds generally do not raise young, but develop a long-term pair bond and build a nest, which they use for many successive years. The nest is built of seaweed, moss and sticks, and grows larger over time as bones, feathers and droppings accumulate around it. Nests are placed 60-90 cm apart- the hexagonal shape of each territory permits the maximum possible number of nests to be squeezed the small breeding area for the colony. Because they nest on cliffs or islands, gannets are relatively safe from terrestrial predators, but they often desert their nests after any disturbance.

In late spring, the female lays one bluish-white egg, which she and her mate take turns incubating. Gannets lack the ‘brood patch’ found in other birds- a special area on the bird’s belly that is adapted to transfer heat to the egg as efficiently as possible. Instead, an incubating gannet crouches on top of its egg, covering it with both of its large, webbed feet. The chick has a long, slow development: incubation takes 44 days, and the parents feed the chick- born naked and helpless, for a further 12-14 weeks. Chicks often leave the nest before they can fly properly, fluttering to the water below, where they subsist on body fat until they have become adept at fishing for themselves.

Northern gannets are vulnerable to human interference. Several colonies are thought to have died out in the 19th century, following the construction of lighthouses nearby. Canadian colonies once held as many as 200,000 individuals, but were decimated in the 19th century by hunting for food and fishing-bait, egg-collecting, the construction of lighthouses, which caused nesting pairs to abandon their nests, and habitat destruction due to erosion. By 1900, only about 8,000 birds were left and strict laws were enacted to outlaw gannet hunting. In the 1960s and 70s, populations declined again after large areas of forest in the Gaspé region were sprayed with the pesticide DDT, which contaminated the gannets’ food supply and caused them to lay thin-shelled eggs that broke during incubation. Fortunately, populations of gannets are now recovering and there are about 90,000 birds in the Maritimes, although they are still menaced by oil spills and other forms of water pollution.