Cape Gannet
Encyclopedia
The Cape Gannet, Morus capensis, originally Sula capensis, is a large seabird
of the gannet
family, Sulidae
.
They are easily identified by their large size, black and white plumage
and distinctive yellow crown and hindneck. The pale blue bill
is pointed with fine serrations near the tip; perhaps because of the depth and speed of the gannet's dive when fishing (depending on altitude, gannets hit the water at speeds of between 40 and 120 kilometers per hourhttp://www.asknature.org/strategy/7055e70a501901f433cf8a3896d93fe4), its beak has no external nostrils into which the water might be forced.
at first glance. Adults are about 84–94 cm (33–37 in) long and have a 171–185 cm (68–73 in) wingspan and weigh ca. 2600 g (5.7 lbs).
Cape Gannets begin breeding in August or September. Typically the clutch is a single bluish egg
, which soon becomes soiled. Both parents are actively involved in the incubation process which lasts for 42 to 46 days until hatching. Gannets use their foot webs to incubate the egg. The foot webs, which are richly irrigated with blood vessels are wrapped around the egg.
The hatchling is black, naked and blind, it weighs only about 70 grams, but within three weeks its body mass is one third of that of an adult. At eight weeks the chick outweighs the adult, and this remains so until it becomes a fledgling at 95–105 days of age.
, but the latter differs from its entirely white tail and its wings, which are only black at the tip.
es. As all Sulids, they are fish-eating birds that plunge-dive from considerable height.
of Cape Gannet is restricted to southern Africa
in three islands off Namibia
and three islands off South Africa
. They normally nest in large and dense colonies on flat islands or on flat ledges of the steeply sloping Mercury Island
off Namibia
. The world population was estimated in 1996 to number about 340,000 birds, with 12% in Namibia
and 88% in South Africa
. The largest colony of this bird, with over 140,000 birds, is found on Malgas Island, South Africa
. Several birds have occasionally been found breeding on offshore Australia
n islands, together with Australasian Gannets, although the Cape species is never represented by more than a few pairs.
The non-breeding range of Cape gannets extends from the coastal waters off the Gulf of Guinea
on the west coast of Africa, to Mozambique
on the east coast. They seldom occur farther offshore than 100 km, though records of birds more than 200 km offshore exist for both the Atlantic and Indian
Oceans.
has been reported for the Cape Gannet on several occasions, but is currently believed to be unproven. Crochet and Haas (2008) examined the status of the species in the western Palearctic region. They list a number of historical claims which had not been accepted by national bird records committees, and analyse the single record which had hitherto been widely accepted, a juvenile recovered offshore from Western Sahara
in 1966. In relation to the latter bird, they conclude that a mistake had occurred; the original data placed the bird inland, in Chad
, with the offshore Western Saharan location being the result of an attempt to correct this to a more plausible location. A (re-)transposition of the original latitude and longitude gives a location off the Namibia
n coast, well within the regular wintering range of the species. As a result, they recommend that Cape Gannet be deleted from the Western Palearctic list.
Seabird
Seabirds are birds that have adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations...
of the gannet
Gannet
Gannets are seabirds comprising the genus Morus, in the family Sulidae, closely related to the boobies.The gannets are large black and white birds with yellow heads. They have long pointed wings and long bills. Northern gannets are the largest seabirds in the North Atlantic, with a wingspan of up...
family, Sulidae
Sulidae
The bird family Sulidae comprises the gannets and boobies. Collectively called sulidas, they are medium-large coastal seabirds that plunge-dive for fish and similar prey. The ten species in this family are often considered congeneric in older sources, placing all in the genus Sula...
.
They are easily identified by their large size, black and white plumage
Plumage
Plumage refers both to the layer of feathers that cover a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage vary between species and subspecies and can also vary between different age classes, sexes, and season. Within species there can also be a...
and distinctive yellow crown and hindneck. The pale blue bill
Beak
The beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young...
is pointed with fine serrations near the tip; perhaps because of the depth and speed of the gannet's dive when fishing (depending on altitude, gannets hit the water at speeds of between 40 and 120 kilometers per hourhttp://www.asknature.org/strategy/7055e70a501901f433cf8a3896d93fe4), its beak has no external nostrils into which the water might be forced.
Morphology
When seen in flight the snow-white body with the black tail, primaries and secondaries, and dark bill makes them easy to identify. At closer range the distinctive golden crown and nape, which gradually becomes white on the neck, is noticeable. Juveniles and Immatures are dark brown with a pale bill, and can resemble the dark-coloured BoobiesBrown Booby
The Brown Booby is a large seabird of the booby family, Sulidae. The adult brown booby reaches about in length. Its head and upper body are covered in dark brown, with the remainder being a contrasting white. The juvenile form is gray-brown with darkening on the head, wings and tail...
at first glance. Adults are about 84–94 cm (33–37 in) long and have a 171–185 cm (68–73 in) wingspan and weigh ca. 2600 g (5.7 lbs).
Breeding biology
Gannet pairs may remain together over several seasons. They perform elaborate greeting rituals at the nest, stretching their bills and necks skywards and gently tapping bills together.Cape Gannets begin breeding in August or September. Typically the clutch is a single bluish egg
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
, which soon becomes soiled. Both parents are actively involved in the incubation process which lasts for 42 to 46 days until hatching. Gannets use their foot webs to incubate the egg. The foot webs, which are richly irrigated with blood vessels are wrapped around the egg.
The hatchling is black, naked and blind, it weighs only about 70 grams, but within three weeks its body mass is one third of that of an adult. At eight weeks the chick outweighs the adult, and this remains so until it becomes a fledgling at 95–105 days of age.
Similar Species
The Cape Gannet is identified from the Australasian Gannet by the all-black tail, a longer black stripe down the throat (from underneath the beak) and more extensive black on the face, but all of these features are difficult to identify unless at close proximity. The Cape Gannet is also very similar to the Northern GannetNorthern Gannet
The Northern Gannet is a seabird and is the largest member of the gannet family, Sulidae.- Description :Young birds are dark brown in their first year, and gradually acquire more white in subsequent seasons until they reach maturity after five years.Adults are long, weigh and have a wingspan...
, but the latter differs from its entirely white tail and its wings, which are only black at the tip.
Feeding
Cape Gannets are powerful fliers, using mainly a flap-gliding technique, which is more energy consuming than the dynamic-soaring favoured by albatrossAlbatross
Albatrosses, of the biological family Diomedeidae, are large seabirds allied to the procellariids, storm-petrels and diving-petrels in the order Procellariiformes . They range widely in the Southern Ocean and the North Pacific...
es. As all Sulids, they are fish-eating birds that plunge-dive from considerable height.
Breeding and non-breeding range
The breeding rangeRange (biology)
In biology, the range or distribution of a species is the geographical area within which that species can be found. Within that range, dispersion is variation in local density.The term is often qualified:...
of Cape Gannet is restricted to southern Africa
Southern Africa
Southern Africa is the southernmost region of the African continent, variably defined by geography or geopolitics. Within the region are numerous territories, including the Republic of South Africa ; nowadays, the simpler term South Africa is generally reserved for the country in English.-UN...
in three islands off Namibia
Namibia
Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March...
and three islands off South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
. They normally nest in large and dense colonies on flat islands or on flat ledges of the steeply sloping Mercury Island
Mercury Island
Mercury Island is a small rocky island off The Diamond Coast, Namibia. Despite its small size it is recognised by Bird Life and other global conservation groups as one of the Important Bird Areas for its important coastal seabird breeding.-Situation:...
off Namibia
Namibia
Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March...
. The world population was estimated in 1996 to number about 340,000 birds, with 12% in Namibia
Namibia
Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March...
and 88% in South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
. The largest colony of this bird, with over 140,000 birds, is found on Malgas Island, South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
. Several birds have occasionally been found breeding on offshore Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
n islands, together with Australasian Gannets, although the Cape species is never represented by more than a few pairs.
The non-breeding range of Cape gannets extends from the coastal waters off the Gulf of Guinea
Gulf of Guinea
The Gulf of Guinea is the northeasternmost part of the tropical Atlantic Ocean between Cape Lopez in Gabon, north and west to Cape Palmas in Liberia. The intersection of the Equator and Prime Meridian is in the gulf....
on the west coast of Africa, to Mozambique
Mozambique
Mozambique, officially the Republic of Mozambique , is a country in southeastern Africa bordered by the Indian Ocean to the east, Tanzania to the north, Malawi and Zambia to the northwest, Zimbabwe to the west and Swaziland and South Africa to the southwest...
on the east coast. They seldom occur farther offshore than 100 km, though records of birds more than 200 km offshore exist for both the Atlantic and Indian
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
Oceans.
Population trends
Numbers of Cape Gannets at the Namibian islands have declined considerably between 1956 and 2000 from 114,600 to 18,200 breeding pairs respectively, an 84% decrease in less than fifty years. This contrasts with the trends at the South African islands where numbers have increased about 4.3 times during the same period, from 34,400 to 148,000 breeding pairs.Vagrancy
Vagrancy to the northern Atlantic OceanAtlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
has been reported for the Cape Gannet on several occasions, but is currently believed to be unproven. Crochet and Haas (2008) examined the status of the species in the western Palearctic region. They list a number of historical claims which had not been accepted by national bird records committees, and analyse the single record which had hitherto been widely accepted, a juvenile recovered offshore from Western Sahara
Western Sahara
Western Sahara is a disputed territory in North Africa, bordered by Morocco to the north, Algeria to the northeast, Mauritania to the east and south, and the Atlantic Ocean to the west. Its surface area amounts to . It is one of the most sparsely populated territories in the world, mainly...
in 1966. In relation to the latter bird, they conclude that a mistake had occurred; the original data placed the bird inland, in Chad
Chad
Chad , officially known as the Republic of Chad, is a landlocked country in Central Africa. It is bordered by Libya to the north, Sudan to the east, the Central African Republic to the south, Cameroon and Nigeria to the southwest, and Niger to the west...
, with the offshore Western Saharan location being the result of an attempt to correct this to a more plausible location. A (re-)transposition of the original latitude and longitude gives a location off the Namibia
Namibia
Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March...
n coast, well within the regular wintering range of the species. As a result, they recommend that Cape Gannet be deleted from the Western Palearctic list.
Further reading
- Crawford 1997. Cape Gannet. In: The Atlas of Southern African Birds Vol. 1: Non-passerines. Harrison, J. A. Allan, D. G., Underhill. L. G., Herremans, M., Tree, A.J., Parker, V. & Brown, C.J. (eds), pp. 28–29. BirdLife South Africa, Johannesburg.
- du Toit, M. & Cooper, J. 2002. Cape Gannet. In: Proposal for inclusion of species in Annex 2 of the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWAAEWAThe Agreement on the Conservation of African-Eurasian Migratory Waterbirds is the largest of its kind developed so far under the Bonn Convention. It was concluded on 16 June 1995 at The Hague, the Netherlands and entered into force on 1 November 1999 after the required number of at least fourteen...
, an agreement under UNEP/CMS). Avian Demography Unit, Cape Town.
External links
- BirdLife Species Factsheet.
- Cape Gannet Avian Demography Unit Fact sheets on Southern African seabirds
- ARKive - images and movies of the cape gannet (Morus capensis)
- Beak protects during dives: cape gannet
- Spinning makes safe dive