Northern gannets are found in the cold, temperate waters of the northern Atlantic over the continental shelves. They are found as far north as the arctic and as far south as subtropical east and west Atlantic coasts. They are typically concentrated within 500 km of breeding colonies during the summer and are more widely dispersed in the winter, occurring as far south as the Gulf of Mexico or rarely into the Caribbean in their western range and as far south as northwestern Africa and the Cape Verde Islands in their eastern range. Although some trans-Atlantic movements have been recorded, there seems to be no substantial exchange of individuals between the eastern and western Atlantic.

Biogeographic Regions: nearctic (Native ); palearctic (Native ); atlantic ocean (Native )

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Transient

Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Breeds on islands in eastern North America in Gulf of St. Lawrence, off Quebec, in Newfoundland, in Nova Scotia, and off New Brunswick; and in eastern North Atlantic. Ranges at sea in breeding regions and south to Florida and the northern Gulf of Mexico. In winter in North America, abundance is highly variable from year to year at a particular location; highest densities have been recorded in eastern North Carolina (Root 1988).

Northern gannets are the largest seabirds in the northern Atlantic. Males are slightly larger than females, although they are similar in plumage. Males are from 93 to 110 cm in length, females from 92.5 to 104 cm. Mass is from 2470 to 3610 grams, with females averaging heavier than males (female average: 3067, male average: 2932). Wing length is from 484 to 535 mm. Adults are white with black-tipped wings and a yellowish crown and nape. The bill is pale blue with black nasal grooves and a black, serrated mandible. The feet and legs are gray-black with a greenish line running down the front of the leg and onto the toes. The line is yellow-green in males and bluish-green in females. The feet have well-developed webbing. The skin of the face is blue-gray and the eye has a bright blue orbital ring with a pale blue-gray iris. The bill is stout and straight and the maxilla overhangs the mandible slightly. The tail is long and tapers to a point.

Juveniles are gray, mixed with white feathers. There is a V-shaped white patch on the rump. The bill, legs, and feet are black and they have bluish grey eyes. With each successive molt more white plumage develops, starting with the lower body and belly and moving progressively upwards to include the head, neck, and breast. Molts are erratic and there is no discernible pattern. Young at fledging weigh substantially more than adults, sometimes more than 4 kg. This weight is lost within 7 to 10 days of fledging, at which point they acheive an adult weight. Development of adult plumage takes 3 to 4 years.

In the northern part of their range northern gannets are unlikely to be confused with other seabirds, although they may be mistaken for shearwaters at a distance. In the southern part of their range they may be confused with masked boobies (Sula dactylatra) or other gannets (Morus capensis). There are no described subspecies of Morus bassanus.

Basal metabolic rate of northern gannets at a breeding colony was estimated at 0.231 kJ/g/d ± 0.035 SE. Basal metabolic rates are considered high, relative to those of other seabirds, because of the high cost of flapping flight at sea and the high cost of thermoregulation in their cold water environment.

Range mass: 2470 to 3610 g.

Range length: 92.5 to 110 cm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: sexes alike

Length: 94 cm

Weight: 3067 grams

• Terrestrial
• Marine

Northern gannets are found in coastal, marine waters on the west and eastern coasts of the north Atlantic. They are found on the ocean at all times of the year, except when they come to land to breed in the summer. Breeding colonies are densely populated and found on sea stacks, steep cliffs, or uninhabited islands. Nests on cliffs and ledges are from just above the high water splash zone to over 200 meters. The suitability of breeding areas is determined by their proximity to good foraging, absence of terrestrial (mammalian) predators, and the presence of good updrafts for taking off and landing.

Habitat Regions: temperate ; terrestrial ; saltwater or marine

Aquatic Biomes: coastal

Comments: Coastal waters primarily but sometimes several hundred miles out to sea. Spends first 3 years of life at sea all year. Nests primarily on open ground on flat-topped islands, less frequently on rocky slopes and cliffs along coasts (AOU 1983).

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.

Off the eastern coast of North America migrates southward from early September into December, returns north from March into April and May. First year birds travel farther south than do adults (Palmer 1962).

A substantial body of literature documents foraging behavior in northern gannets. Northern gannets eat mainly schooling fish found at the surface of oceans or seas, up to 15 m deep. Prey fish are from 2.5 to 30.5 cm in length. They also eat surface schools of squid. They often feed in association with predatory fish and cetaceans, such as bluefish (Pomatomus saltatrix), white-beaked dolphins (Lagenorhynchus albirostris), and Atlantic white-sided dolphins (Lagenorhynchus acutus). Northern gannets forage over shallow, continental shelf waters. They typically range 60 to 232 km from colonies to forage, but can range up to 540 km. Foraging expeditions are typically 7 to 14 hours long, but can last several days. Northern gannets do forage on their own, but more commonly they forage in large flocks (up to 1000) over schools of fish. Research indicates that when resources are predictable, northern gannets learn and remember feeding locations, revisiting them over a period of time. This is not observed in areas where resources are less predictable. Northern gannets generally spend about half of foraging trip duration in flight to a foraging area. Northern gannets travel at an average speed of 15 km per hour during foraging trips, although their maximum flight speed is 55 km per hour. Foraging activity is concentrated in mornings and late afternoon, with a mid-day lull and no activity at night.

Northern gannets are generalists and opportunistic in foraging, although their body size and foraging style allows them to take advantage an oil-rich source of fish prey that is abundant in the size class they take. Their size also helps them to withstand the punishing environmental conditions in the areas these fish are found. Northern gannets use mainly "plunge-diving," in which they dive from 10 to 40 meters above the water, entering at over 100 km/hr to depths of 3 to 5 meters. They can then swim to depths up to 15 meters after a dive. They use both wings and feet when they swim and can be submerged up to 30 seconds, although 5 to 7 seconds is more typical. Most dives (90%) are less than 10 meters deep. Northern gannets have also been observed feeding from the water's surface by dipping their heads into the water, diving in from the water to pursue prey, foraging in shallow water on foot, or stealing prey from other seabirds.

The composition of the diet varies substantially with region. The dominant prey species throughout most of their range are mackerel and herring (Clupea harengus) species. In some areas dominant prey are capelin (Mallotus villosus), coalfish (Pollachius virens), cod (Gadus morhua), whiting (Merlangius merlangus), haddock (Melanogrammus aeglefinus), sprat (Sprattus sprattus), pilchard (Sardina pilchardus), and garfish (Belone belone), and short-finned squid (Illex illecebrosus). Other recorded prey species include: sandlance (Ammodytes hexapterus), sandeels (Hyperoplus), smelt (Osmerus mordax), menhaden (Brevoortia), flounder (Pleuronectes), long-finned squid (Loligo pealei), and shrimp (Crangon). Northern gannets also follow commercial fishing ships and consume both fish discarded from catches and fish in nets, including species of fish not normally part of their diet because they are not found at the surface. Northern gannets are most successful at taking larger fish discarded from fishing vessels. They are one of the few species that has been recorded preying on marine-phase salmon, especially Salmo salar, which can make up a significant portion of the diet in some colonies (up to 6.37%).

Animal Foods: fish; mollusks

Primary Diet: carnivore (Piscivore )

Comments: Eats surface schooling fishes; dives into water from air, swims underwater to depth of 50 feet at most (Terres 1980).

Northern gannets have been found with protozoan (Sarcocystis) infections in the brain linked to their definitive hosts, Virginia opossums (Didelphis virginianus). This has been taken to suggest that wastewater discharge into marine environments can result in infection of marine species with terrestrial-based parasites.

Northern gannets do not seem to be highly susceptible to disease epidemics, although some mortality associated with Salmonella typhimurium, Newcastle disease virus, and aspergillosis (Aspergillus fumigatus) has been reported. Northern gannets are parasitized by mites (Neottialges evansi), trematode worms (Cryptocotyle lingua and Diplostomum spathaceum), and diplostomes (Bursatintinnabulus bassanus and Bursacetabulus morus).

Northern gannets feed in association with larger, predatory fish and cetaceans, including bluefish (Pomatomus saltatrix), white-beaked dolphins (Lagenorhynchus albirostris), and Atlantic white-sided dolphins (Lagenorhynchus acutus).

Mutualist Species:

• bluefish (Pomatomus saltatrix)
• white-beaked dolphins (Lagenorhynchus albirostris)
• Atlantic white-sided dolphins (Lagenorhynchus acutus)

Commensal/Parasitic Species:

• Sarcocystis
• mites (Neottialges evansi)
• trematode worms (Cryptocotyle lingua)
• trematode worms (Diplostomum spathaceum)
• diplostomes (Bursatintinnabulus bassanus)
• diplostomes (Bursacetabulus morus)
• Salmonella typhimurium
• aspergillosis (Aspergillus fumigatus)

Northern gannets suffer relatively small amounts of predation. Eggs are occasionally taken by great black-backed gulls (Larus marinus), herring gulls (Larus argentatus), common ravens (Corvus corax), red foxes (Vulpes vulpes), or short-tailed weasels (Mustela erminea). Nestlings may be taken by the same predators as well as bald eagles (Haliaeetus leucocephalus). Adult northern gannets are generally safe from predation, although fledglings and occasional adults that are on the water may be taken by a large fish, shark, or seal. Northern gannets are large and will aggressively encounter a predator that approaches the breeding area.

Known Predators:

• great black-backed gulls (Larus marinus)
• herring gulls (Larus argentatus)
• common ravens (Corvus corax)
• red foxes (Vulpes vulpes)
• short-tailed weasels (Mustela erminea)
• bald eagles (Haliaeetus leucocephalus)

100,000 - 1,000,000 individuals

Comments: In 1960s, world breeding population about 426,000 (Tufts 1961). In Canada, total population was 44,200 pairs in the late 1980s (Nettleship, in Hyslop and Kennedy 1992).

Post-fledging mortality in first year may be high (see Montevecchi et al. 1984).

Northern gannets communicate with a wide variety of calls and visual displays. Many displays seem to be associated with maintaining territorial control in their densely packed breeding colonies. Displays include several threat displays that involve stereotyped jabbing and gaping. Threats are also communicated with a bowing display that involves thrusting the head and body forward several times and then tucking the bill against the breast. Appeasement is communicated with tucking the bill against the breast or otherwise hiding the bill in both adults and nestlings.

Northern gannets are noisy birds, especially when in large groups. They use a wide array of vocalizations. Young give cheeping calls when hatching, yap in response to trespassers in their nesting area, and beg for food from parents. Adult vocalizations have been grouped into 3 types: 1) landing calls are harsh calls used when landing and in bowing, mutual fencing, and threat displays - they are described as loud, metallic, repeated "urrah"s, "rah rah" calls are alarm versions of the "urrah," which are staccato and loud, 2) hollow groans are used when taking off or after short hops or runs, 3) soft "krok krok" sounds are given when gannets are swimming at sea or in low flight over the water.

Communication Channels: visual ; acoustic

The oldest wild northern gannet was estimated to be 21 years old. Mortality is highest in the first year after hatching, with very high mortality rates during the period just after fledging when immature individuals cannot fly. About 65% of immature northern gannets do not survive to adulthood. Little mortality is associated with the pre-fledging period because breeding colonies are found in areas with few predators and because gannet parents incubate and brood their young continuously in their cold-weather habitats. Yearly mortality rates of adults are estimated to be less than 6%.

Range lifespan

Status: wild: 21 (high) years.

Northern gannets form monogamous bonds for life. At maturity, males attempt to secure a breeding territory and then attract a mate. Males initially compete for breeding spots, but after mating both males and females aggressively defend and fight for breeding sites. Fighting for good breeding spots - ones that are near or in a breeding colony - can be fierce and sometime result in death. Physical interactions are accompanied by calling and displays, fights generally involve locking bills and pushing. Gannets can even push themselves off of cliffs, where fights continue in the air. Jabbing with the bill is used to keep neighbors away from a nest site once it is established. Males attract females with a "headshake-and-reach," in which they shake their head and dip their bill towards the nest. The first few weeks of a new pair bond are tenuous and females may desert the male for another. After forming a longer term pair bond, however, mates are paired for life. The pair bond is reinforced with headshakes, nape biting, allopreening, and "mutual fencing," in which they stand facing each other and knock their bills together by shaking their hides side to side. Once mated, pairs return to the same breeding site every year; in one study 94% of males and 88% of females returned to the same nest site the next year.

Mating System: monogamous

Northern gannets breed in 32 colonies in the eastern Atlantic and only 6 colonies in North America. Breeding colonies are large and densely populated, found on rocky cliffs, islands, and stacks. Nests are re-occupied by pairs each year. They add nest materials to the nest after arriving at the breeding colony. Females lay a single egg from the end of April through mid June. Females may lay up to 3 replacement eggs if they are lost, even after up to 26 days of incubation. Eggs are about 105 grams and are pale blue-green that becomes thick with a chalky outer layer as incubation progresses. Hatching occurs from early June to early July, with a peak in mid-June. Young are then brooded for about 13 weeks until fledging, in September. Hatchling growth is rapid, going from about 79.3 grams at hatching to over 4 kg at 10 weeks old, at which point they weigh more than adults.

Breeding interval: Northern gannets breed once yearly.

Breeding season: Northern gannets breed in the summer, from April through mid-June.

Range eggs per season: 1 (high) .

Average eggs per season: 1.

Range time to hatching: 42 to 46 days.

Average birth mass: 79.3 g.

Average fledging age: 90 days.

Average time to independence: 90 days.

Average age at sexual or reproductive maturity (female): 3 years.

Average age at sexual or reproductive maturity (male): 3 years.

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate)

Young are altricial at hatching and eggs and young are continuously incubated or brooded on the vascularized webbing of their parent's feet. Adults do not develop a brood patch. Young are naked with a thin layer of creamy down. All downy plumage is lost by 11 to 12 weeks old. Both males and females incubate, brood, feed, and protect the young. Females spend more time (74%) incubating than males. Eggs and young are continually attended by a parent. When a mate comes to take over incubation, an elaborate display ensues. Similar to breeding, males and females engage in mutual fencing and nape biting as they prepare to exchange places. The parent that has been relieved from the nest then does a "skypointing" display in which they stand with the bill held vertically, spreads the wings upwards, and alternates lifting the feet, accompanied by an "ooh-ah" vocalization. Hatchlings are fed by regurgitation by their parents. Once young gannets have fledged, they disperse from the breeding colony. Fledglings glide off a cliff ledge into the sea and begin to swim south towards their wintering range. Because of their inexperience and large body mass, they are unable to fly for their first week after fledging. Once they can fly, they continue their migration to wintering grounds.

Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female)

Single egg is laid in April-May. Incubation, by both sexes, lasts 42-44 days. Young are tended by both parents at nest for about 84-87 days. Begins breeding at 5-7 years. Breeds in large colonies (1000s of pairs in most cases).

Northern gannet populations appear to be stable and the IUCN lists them as least concern. Population estimates are approximately 530,000 individuals globally and a range extent of from 50,000 to 100,000 square kilometers. In portions of their range, northern gannet populations seem to have grown substantially - with increases by a factor of 2.4 between 1977 and 1999. Overall, colonies seem to be increasing by 3 to 3.5% yearly. Increases in North American populations may be partially the result of bans on DDT use. The Migratory Birds Convention Act of 1917 in Canada and Migratory Bird Treaty Act of 1918 in the U.S. protected breeding colonies. Previously, gannet colonies were exploited by fishermen for bait and were persecuted as competition for fish. Their habit of feeding on fish in nets leads to a fair amount of mortality through entanglement with nets and gear or through direct killing by fishermen. Northern gannets are not substantially affected by oil spills, but toxic chemicals and heavy metals, such as PCB's, mercury, and cadmium, accumulate in their tissues because of their trophic status. Populations may be limited by the availability of suitable breeding colony sites.

US Migratory Bird Act: protected

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

Regular passage visitor and winter visitor.

Canada

Rounded National Status Rank: N4B,N5N : N4B: Apparently Secure - Breeding, N5N: Secure - Nonbreeding

United States

Rounded National Status Rank: NNA - Not Applicable

Rounded Global Status Rank: G5 - Secure

Because of their large population sizes and concentration near breeding colonies, northern gannet foraging can impact fish availability. Estimates in Newfoundland suggest that the annual intake of mackerel and squid by northern gannets is greater than the total commercial take.

Monitoring northern gannet diet has been used as a way of estimating prey species abundance and distribution, such as populations of Atlantic salmon in eastern Canada (Salmo salar).

Comments: Formerly included in genus Sula, but transferred to Morus by AOU (1989). S. capensis and S. serrator may be subspecies of M. bassanus (Sibley and Monroe 1990).