L’habitat est marin, l’espèce circulant presque exclusivement le long du plateau continental. Elle s’approche du trait de côte uniquement lors des transits vers et depuis les sites de nidification, lors d’événements météorologiques, ou encore lorsqu’elle suit les bancs de poissons. Le Fou s’installe en colonie sur des îlots rocheux, le nid étant si possible situé sur une corniche au-dessus de l’eau. Autour de la principale colonie française, la zone d’alimentation s’étend jusqu’à 180 km.
Le Fou de Bassan se nourrit de poissons qu’il capture en plongeant d’une hauteur atteignant parfois 40 m et qu’il avale lors de la remontée en surface.
L’espèce est fortement grégaire, y compris pendant la pêche sur les bancs de poissons. Les jeunes restent solitaires jusqu’à ce qu’ils sachent décoller de la surface de l’eau ; ils s’associent ensuite aux groupes en recherche alimentaire. Le Fou est monogame et les mêmes couples se reforment chaque année. La formation d’un couple peut débuter à l’âge de 3 ans mais la reproduction n’a pas lieu avant la 5e année. La compétition pour les sites de nid les plus adéquats est intense, les nids étant pratiquement en contact les uns des autres. De bruyants combats ont lieu, qui peuvent se poursuivre dans les airs ou dans l’eau. Les rituels qui unissent le couple sont nombreux et complexes.
L’œuf unique est déposé entre mi-avril et mi-juin dans un nid fait d’algues, d’herbes, de plumes et de terre, le tout cimenté par les excréments. L’incubation dure entre 42 et 46 jours et le jeune s’envole à l’âge de 3 mois. Le Fou de Bassan est en augmentation à l’échelle nationale comme à l’échelle mondiale.
- North-West Atlantic Ocean species (NWARMS)
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 )
- Mowbray, T. 2002. Northern Gannet (Morus bassanus). Pp. 1-10 in A Poole, ed. The Birds of North America Online, Vol. 693. Ithaca: Cornell Lab of Ornithology. Accessed January 28, 2009 at http://bna.birds.cornell.edu/bna/species/693.
Regularity: Regularly occurring
Type of Residency: Year-round
Regularity: Regularly occurring
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
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
Habitat and Ecology
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).
Water temperature and chemistry ranges based on 92678 samples.
Depth range (m): 0 - 750
Temperature range (°C): -0.062 - 27.624
Nitrate (umol/L): 0.184 - 18.043
Salinity (PPS): 19.618 - 37.870
Oxygen (ml/l): 4.607 - 8.415
Phosphate (umol/l): 0.057 - 1.226
Silicate (umol/l): 0.565 - 12.289
Depth range (m): 0 - 750
Temperature range (°C): -0.062 - 27.624
Nitrate (umol/L): 0.184 - 18.043
Salinity (PPS): 19.618 - 37.870
Oxygen (ml/l): 4.607 - 8.415
Phosphate (umol/l): 0.057 - 1.226
Silicate (umol/l): 0.565 - 12.289
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.
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 pallasii pallasii) 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 )
- Camphuysen, C., H. Heessen, C. Winter. 1995. Distant feeding and associations with cetaceans of gannets Morus bassanus from the Bass Rock. Seabird, 17: 36-43.
- Garthe, S., O. Huppop. 1994. Distribution of ship-following seabirds and their utilization of discards in the North Sea in summer. Marine Ecology, 106: 1-9.
- Garthe, S., S. Benvenuti, W. Montevecchi. 2003. Temporal patterns of foraging activities of northern gannets, Morus bassanus, in the northwest Atlantic Ocean. Canadian Journal of Zoology, 81: 453-461.
- Hamer, K., R. Phillips, S. Wanless, M. Harris, A. Wood. 2000. Foraging ranges, diets and feeding locations of gannets Morus bassanus in the North Sea: evidence from satellite telemetry. Marine Ecology, 200: 257-264.
- Montevecchi, W., D. Cairns, R. Myers. 2002. Predation on marine-phase Atlantic salmon (Salmo salar) by gannets (Morus bassanus) in the Northwest Atlantic. Canadian Journal of Fisheries and Aquatic Science, 59: 602-612.
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).
- bluefish (Pomatomus saltatrix)
- white-beaked dolphins (Lagenorhynchus albirostris)
- Atlantic white-sided dolphins (Lagenorhynchus acutus)
- Spalding, M., C. Yowell, D. Lindsay, E. Greiner, J. Dame. 2002. Sarcocystis meningoencephalitis in a northern gannet (Morus bassanus). Journal of Wildlife Diseases, 38: 432-437.
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.
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).
Life History and Behavior
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
Perception Channels: visual ; tactile ; acoustic ; chemical
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%.
Status: wild: 21 (high) years.
Lifespan, longevity, and ageing
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 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: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous
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)
- Huettmann, F., A. Diamond. 2000. Seabird migration in the Canadian northwest Atlantic Ocean: moulting locations and movement patterns of immature birds. Canadian Journal of Zoology, 78: 624-627.
- Mowbray, T. 2002. Northern Gannet (Morus bassanus). Pp. 1-10 in A Poole, ed. The Birds of North America Online, Vol. 693. Ithaca: Cornell Lab of Ornithology. Accessed January 28, 2009 at http://bna.birds.cornell.edu/bna/species/693.
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).
Molecular Biology and Genetics
Barcode data: Morus bassanus
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Morus bassanus
Public Records: 13
Specimens with Barcodes: 13
Species With Barcodes: 1
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
- BirdLife International 2008, 2008. "Morus bassanus" (On-line). IUCN Redlist of Endangered Species. Accessed February 02, 2009 at http://www.iucnredlist.org/details/144611.
IUCN Red List Assessment
Red List Category
Red List Criteria
National NatureServe Conservation Status
Rounded National Status Rank: N4B,N5N : N4B: Apparently Secure - Breeding, N5N: Secure - Nonbreeding
Rounded National Status Rank: NNA - Not Applicable
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Status in Egypt
Regular passage visitor and winter visitor.
Relevance to Humans and Ecosystems
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.
The northern gannet (Morus bassanus) is a seabird and it is the largest member of the gannet family, Sulidae. It has the same colours as the Australasian gannet and is similar in appearance. Nesting in colonies as large as 60,000 pairs on both sides of the north Atlantic this bird undertakes seasonal migrations and is a spectacular high-speed diver.
Old names for the northern gannet include solan and solan goose.
- 1 Description
- 2 Distribution
- 3 Conservation status
- 4 Depredation
- 5 Diet and foraging
- 6 Reproduction
- 7 Migration
- 8 Gallery
- 9 References
- 10 Bibliography
- 11 External links
Adults are 81–110 cm (32–43 in) long, weigh 2.2–3.6 kg (4.9–7.9 lb) and have a 165–180 cm (65–71 in) wingspan. Before fledging, the immature birds (at about 10 weeks of age) can weigh more than 4 kg (8.8 lb). Each wing measures between 47 and 53 cm (19 and 21 in) when outstretched and the beak measures between 9 and 11 cm (3.5 and 4.3 in) (measured from the head). The two sexes are a similar size.
The plumage of the adults is white with dark wing tips, with colours that range from brown to black. The colour of the head, cheeks and side of the neck depends on the season and the individual; during breeding, the head and neck are brushed in a delicate yellow, although this colouring may not be evident in some individuals. 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 their head. The eye is light blue, and it is surrounded by bare, black skin, which gives the birds their characteristic facial expression.
Fledglings are brown with white wing tips. They have white spots on their head and on their back and a v-shaped white area underneath. The plumage of one-year-olds can be almost completely brown. In the second year the birds’ 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. They gradually acquire more white in subsequent seasons until they reach maturity after five years.
Newborn chicks are featherless and are dark blue or black in colour. In the second week of life they are covered in white down. From the fifth week they are covered in dark brown feathers flecked with white.
Their beak is long, strong and conical with a slight downward curve at the end. The front part has a sharp edge. In adults, the beak is blue-grey with dark grey or black edges. It is brownish in immature birds.
The northern gannet’s eyes are large and point forwards, and they have a light blue to light grey iris surrounded by a thin black ring. The four toes of their feet are joined by a membrane that can vary from dark grey to dark brown. There are yellow lines running along the toes that continue along their legs; these lines probably have a role in mating. The rear toe is strong and faces inwards allowing the birds to firmly grip onto vertical cliff faces.
Distinguishing anatomical features
Northern gannets dive vertically into the sea at velocities of up to 100 km/h (62 mph) and the structure of their bodies is adapted for this practice. They do not have external nostrils and their secondary nostrils can be closed when they are in water. The opening of their auditory canal is very small and is covered with feathers; the openings can also be closed in water using a system that is similar to that used for the nostrils. The sternum is very strong and sufficiently long to provide protection for the internal organs from impacts with water.
The lungs are highly developed and probably also play a role in reducing the effects of hitting water at high speeds and protect the body from these effects. There are subcutaneous air sacks in the lower body and along the sides. Other air sacks are located between the sternum and the pectoral muscles and between the ribs and the intercostal muscles. These sacks are connected to the lungs and are filled with air when the bird breathes in. The air can be expelled by muscle contractions.
Individuals have a subcutaneous fat layer, dense down 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 they swim.
By air, land and sea
The wings of the northern gannet are long and narrow and they are positioned towards the front of the body, allowing efficient use of air currents when flying. Even in calm weather they can attain velocities of between 55 and 65 km/h (34 and 40 mph) even though their flying muscles are not highly developed: in other birds flying muscles make up around 20% of total weight, while in northern gannets the flying muscles are less than 13%. The consequence of this is that northern gannets need to warm up before they begin flying. They also walk with difficulty and this means that they have difficulty taking off from a flat area. They take off from water by facing into the wind and strongly beating their wings. In light winds and high waves they are sometimes unable to take off and they can become beached. They take advantage of the wind produced by the front of a wave in the same way as the albatross does. They are only seen inland when they have been blown off-course by storms.
They alight on water with their feet retracted. They rarely land on water with their feet stretched forward like pelicans or cormorants. When they are on the water their body is rather low in the water with their tail pointing diagonally upwards. They alight with difficulty on land and often alight with a bump as their narrow wings do not allow them to turn easily and they have to use their feet and tail to aid in these manoeuvres. Individuals often suffer damage to their legs or feet when they land on the ground if there is not sufficient wind. Damaged or broken wings are a frequent cause of death in adults. The position of the legs towards the rear of the body means that they walk in a similar way to ducks.
The northern gannet does not have a very characteristic acoustic repertory. Its typical call is rab-rab-rab, which is emitted when fishing and also when on the nest. They have a special call when they approach the colony: this call is often heard because there is usually a lot of toing and froing in a colony. Males and females make similar calls.
According to the ornithologist Bryan Nelson northern gannets can recognize the call of their breeding partner, chicks and birds in neighbouring nests. Individuals from outside this sphere are treated with more aggression.
Their breeding range is the North Atlantic on coasts influenced by the Gulf Stream, the exception being the colonies of the Gulf of Saint Lawrence and the islands off the east coast of Canada. They normally nest in large colonies, on cliffs overlooking the ocean or on small rocky islands. The waters near to these cliffs have a summer temperature at the surface of between 10 and 15 °C (50 and 59 °F). The water temperature determines the distribution of Atlantic mackerel and herring, which are the main food source for the northern gannet. For this reason there is a close relationship between the location of northern gannet breeding colonies and the distribution of these fish. Northern gannet colonies can be found in the far north in regions that are very cold and stormy. The ornithologist Bryan Nelson has suggested that they can survive in these regions due to a number of factors including: the combination of body weight and a strong beak that allows them to capture strong muscly fish and the ability to dive to great depths and capture prey far from the cliffs. In addition they are able to stand long periods without eating owing to their large fat reserves.
The northern limit of their breeding area depends on the presence of waters that are free of sea ice during the breeding season. Therefore, while Greenland and Spitsbergen offer suitable breeding sites, the arctic regions have summers that are too short to allow the northern gannets to lay their eggs and raise a brood, which requires between 26 and 30 weeks. The southern limit of their distribution mainly depends on the presence of sufficient prey.
The species is a rare visitor in the Black Sea region.
Some breeding colonies have been recorded as being located in the same place for hundreds of years. The cliffs containing the colonies appear to be covered in snow when seen from a distance, due to the number of nests present on them. There is a written record of a colony on the island of Lundy from 1274. It noted that the population was declining due to hunting and the theft of eggs. The colony finally disappeared in 1909. 68% of the world population breeds around the coasts of Great Britain and Ireland. The biggest colonies include:
- Bass Rock off the east coast of Scotland, first recorded in 1448. In 2004, it contained more than 48 000 nests. This is where part of the species’ Latin name comes from.
- Saint Kilda and Sula Sgeir, in the Hebrides. Saint Kilda is the largest colony in Europe with more than 60 000 nests.
- Eldey off Iceland, where between 14 000 and 15 000 pairs breed.
Other European colonies are found in the south west of Ireland, and off the west (Runde Island) and north of Norway (Syltefjord, Hovflesa and Storstappen). The most southerly European colony is on the island of Rouzic off the French Atlantic coast. There are breeding colonies along the coast of Newfoundland and on the islands in the Gulf of Saint Lawrence. The largest colony has 32 000 nests and is on Bonaventure Island off the south coast of Quebec.
A 2004 survey counted 45 breeding colonies and some 361 000 nests. The population is apparently growing between 3 and 5% a year, although this growth is concentrated in just a few colonies. Although northern gannet populations are now stable, their numbers were once greatly reduced due to loss of habitat, removal of eggs and killing of adults for their meat and feathers. In 1939, there were 22 colonies and some 83 000 nests, which means that the populations have increased fourfold since that time. This increase in numbers could also be due to northern gannets benefiting from the growing activities of deep sea fishing.
In 1992, the International Union for the Conservation of Nature (IUCN) estimated the bird’s population to be some 526 000. However, taking into account an estimate produced for BirdLife International in 2004 of the European population, the IUCN revised its global population to between 950 000 and 1 200 000 individuals.
The IUCN lists northern gannets as a species of least concern, as they are widely distributed, do not fulfil many of the criteria set for vulnerable species, and as there is a large population that appears to be growing.
In the United Kingdom, gannets are a protected species. However, a legal exception is made for the inhabitants of the district of Ness (also known as Nis) of the Isle of Lewis in Scotland's Outer Hebrides, who are allowed to cull up to 2,000 gannets (locally known as guga) annually to serve as a traditional local delicacy—the taste is described as fishy. Many of these gannets are taken from Sula Sgeir, which is itself named after them.
Predators of eggs and nestlings include the great black-backed gull and American herring gull, common ravens, ermine, and red fox. Predation at sea is insignificant though large sharks and seals may rarely snatch a gannet out at sea.
Diet and foraging
Northern gannets forage for food during the day, generally by diving into the sea. They search for food both near to their nesting sites but also further out to sea. Birds that are feeding young have been recorded searching for food up to 320 km (200 mi) from their nest. It has been found that 2% of birds nesting in the colony on Bass Rock search for fish at Dogger Bank, between 280 and 320 km (170 and 200 mi) away. It is likely that they fly greater distances than this while searching for food, possibly up to double this distance; however, they normally fly less than 150 km (93 mi).
When feeding, these birds are spectacular high-speed divers. They can locate their prey from heights of up to 45 m (148 ft), but they normally search from a height of between 10 and 20 m (33 and 66 ft). When they see a fish they will dive into the water. They dive with their bodies straight and rigid, wings tucked close to the body but reaching back, extending beyond the tail, before piercing the water like an arrow. They control the direction of the dive using their wings. Just as it is going to hit the water a bird will fold its wings against its body. A bird’s head and neck are stretched out in front of the body and the beak is shut. Birds can hit the water at speeds of up to 100 km/h (62 mph). This allows them to penetrate 3–5 m (10–16 ft) below the surface, and occasionally they will swim down to 12–15 m (40–50 ft).
They usually push their prey deeper into the water and capture it as they return to the surface. When a dive is successful, gannets swallow the fish underwater before surfacing, and never fly with the fish in their bill. Larger fish are swallowed headfirst, smaller fish are swallowed sideways or tail first. The bird’s subcutaneous air bags aid their rapid return to the surface.
Their white colour helps other gannets to identify one of their kind and they can deduce the presence of a shoal of fish by this diving behaviour; this in turn facilitates group foraging, which makes capturing their prey easier. Northern gannets also forage for fish while swimming with their head under water.
Some studies have found that the duration and direction of flights made while foraging for food are similar for both sexes. However, there are significant differences in the search behaviour of males and females. Female northern gannets are not only more selective than males in choosing a search area: they also make longer and deeper dives and spend more time floating on the surface than males.
They eat mainly fish 2.5–30.5 cm (0.98–12.01 in) in length which shoal near the surface. Virtually any small fish (roughly 80–90% of their diet) or other small pelagic species (largely squid) will be taken opportunistically. Sardines, anchovies, haddock, smelt, Atlantic cod and other shoal-forming species are eaten. In the case of the larger fish species northern gannets will only eat the young fish.
They will also follow fishing boats with the hope of finding food in the same was as gulls do. They fly around the boats to take fish from the fishing nets or pick up the remains thrown into the sea.
The oldest birds are the first to return to the breeding colonies. The exact duration of the breeding season depends on the colony’s geographic location: the breeding season on Bass Rock starts in the middle of January, that of Iceland at the end of March or in April. The birds that are not of breeding age arrive a few weeks later. In general, birds first return to a colony (not necessarily the one they were born in) when they are two or three years old. It is not unusual for birds to change colony before they reach breeding age, but once an individual has successfully bred in a colony it will not change to another.
Immature birds stay on the edges of the colony. They may even make a nest but they will not breed until they are four or five years old. Some birds of this age will occupy empty nests that they will aggressively defend if they have sat on them for two or three days. If an apparently empty nest has an owner the immature bird will abandon it without putting up a struggle when the owner arrives to claim the nest.
The preferred nesting sites are on coastal hillsides or cliffs. If these sites are not available northern gannets will nest in groups on islands or flat surfaces. As they find it more difficult to take off from these locations they will often cross the area occupied by an adjacent nest causing an aggressive reaction from the pair occupying that nest; this means that the stress levels are higher in this type of colony than in those on more vertical surfaces. Notwithstanding this, nests are always built close together and ideal nesting sites will not be used if they are some distance from a colony. On average there are 2.3 nests per square metre.
Nests are made from seaweed, plants, earth and all types of object that float on the sea. The males usually collect the materials. Nests measure between 50 and 70 cm (20 and 28 in) in diameter and are some 30 cm (12 in) in height; during the course of a breeding season they will sustain damage from the wind and other causes and they require frequent maintenance. The area which a nest occupies grows throughout the breeding season as the breeding pairs throw their excrement outside the nest.
Aggressive behaviour on the nest
Northern gannets exhibit many types of aggressive behaviour while they are nesting. Confrontations normally only take place between birds of the same sex. Females will lower their heads before an aggressive male that is defending its nest: this will expose the back of the female’s neck and the male will take it in its beak and expel the female from the nest. A female will not react if a male approaches a nest but it will react fiercely if another female approaches. The fights between males that occupy nests for the first time are particularly intense. Such fights can lead to serious injuries. The fights are preceded by threatening gestures, which are also seen outside the breeding season. Males will demonstrate ownership of a nest by gesturing towards their neighbours with their head with the beak pointing down and the wings slightly outstretched.
Once males have found a place to breed they try to attract an available female. The females will fly over the colony a number of times before landing. Their posture, with the neck stretched out, tells the male that they are available for courtship. The male will then shake their heads in a similar way to when they are guarding their nest but with their wings closed.
Gannet pairs are monogamous and may remain together over several seasons, if not for all their lives. The pairs separate when their chicks leave the nest but they pair up again the following year. Should one of the pair die the other bird will leave the breeding ground and pair up with another single bird.
They fiercely defend the area around their nest. Where space allows, the distance between nests is double the reach of an individual.
Eggs and chicks
Northern gannets only lay one egg that on average weighs 104,5 grams. This is lighter than for other seabirds. Where two eggs are found in a nest this is the result of two females laying an egg in the same nest or one of the eggs has been stolen from another nest. Northern gannets will lay another egg if the first one is lost. Incubation takes 42 to 46 days. During incubation the egg is surrounded by the brooding bird’s webbed feet that are flooded with warming blood. The process of breaking the eggshell can take up to 36 hours. When this is about to take place the brooding bird will release the egg from its webbed feet to prevent the egg from breaking under the adult's weight as the chick breaks it open. This is a frequent cause of death for chicks of birds that are breeding for the first time. The webbed feet are also used to cover the chicks, which are only rarely left alone by their parents. Chicks that are left unattended are often attacked and killed by other northern gannets.
Young chicks are fed regurgitated semi-digested fish by their parents. Older chicks receive whole fish. Unlike the chicks of other species, northern gannet chicks do not move about the nest or flap their wings to ask for food: this reduces the likelihood that they will fall from the nest.
The adults feed their offspring for 11 or 12 weeks, until they are strong enough to leave the nest for good. A chick will glide from the nest down to the sea after 75 days, which will mark the point at which it separates permanently from its parents. Young birds that weigh 4 kg (8.8 lb) at this point will not be able to fly so they are unable to return to the cliff. Their fat reserves allow them to pass two or three weeks without eating. If the young birds leave the nest in bad weather they can be mortally wounded as they can be blown against the rocks.
The young birds are attacked by adults if they enter the breeding ground, so they stay at sea learning to fish and fly. A high proportion of the young birds can die if storms occur at this time.
The young birds migrate southwards for great distances and have even been recorded as far south as Ecuador. In their second year a number of birds return to the colony they were born in, where they arrive after the mature birds, they will then migrate south again at the end of the breeding season. They travel shorter distances in this second migration.
After the breeding season the adults spread out over a wide area although they travel no more than 800 to 1,600 km (500 to 990 mi) from the breeding colony. It is not known if all birds from one colony migrate to the same over-wintering area. Many adults migrate to the west of the Mediterranean, passing over the Strait of Gibraltar and flying over land as little as possible. Other birds follow Africa's Atlantic coastline to arrive in the Gulf of Guinea. Immature northern gannets from colonies in Canada fly to the Gulf of Mexico while the adults do not fly that far.
Northern gannets usually nest close together on cliff ledges.
«Sky pointing», gesture made to signal that a bird is about to fly away from the nest.
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Most plunge-dives are relatively shallow, but the Northern Gannet can dive as deep as 22 meters (72 feet). It uses its wings and feet to swim deeper in pursuit of fish.
In North America, the Northern Gannet breeds in only six well established colonies: three in the Gulf of St. Lawrence, Quebec, and three in the North Atlantic off the coast of Newfoundland. In the eastern North Atlantic, it is distributed in 32 colonies from the coast of Brittany in France northward to Norway.
Names and Taxonomy
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).