Cape gannet (Morus capensis)

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Cape gannet in flight, preparing to land
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Cape gannet fact file

Cape gannet description

KingdomAnimalia
PhylumChordata
ClassAves
OrderPelecaniformes
FamilySulidae
GenusMorus (1)

Cape gannets are easily identified by their large size, silky black and white plumage and the distinctive golden-yellow hue to their crown and hindneck (4). When seen in flight, the black colour of the tail, primaries and secondaries, and stripe down the centre of the throat, provides a striking contrast to the otherwise snow-white body (4) (5). There are also distinctive black lines around the beak and on the face (6). The powerful, pale blue bill is pointed with fine serrations near the tip, and the large feet are webbed between each toe (5) (7). Juveniles are dark brown, and gradually gain increasing amounts of the white feathers of the adult plumage after their first year (2) (3).

French
Fou du Cap.
Size
Size: 84 – 94 cm (2)
Weight
c. 2.6 kg (3)
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Cape gannet biology

Cape gannets first return to breeding colonies after two to three years at sea (8). Males establish a nest territory while females wander on the outskirts of the colony ready to respond to inviting males, who entice females with much calling, head shaking and bowing. Once a mate is found, the pair bond is consolidated with mutual bill fencing and bowing. Partners then cooperate in building a nest and guarding their shared territory. Eggs are mainly laid from mid-October to mid-December, although some birds may lay as early as mid-June (4). The clutch typically consists of a single bluish egg, rarely two, which is then incubated for 42 to 46 days by both parents using the warm webs of their feet, which receive a rich blood supply (4) (5). The hatchling is naked and blind, but by eight weeks it outweighs the adults and continues to do so until it becomes a fledgling at 95 to 105 days of age. Both parents tend to the needs of the fast-growing, ravenous chick, primarily feeding it regurgitated anchovy (Engraulis capensis) and sardine (Sardinops ocellatus). Before fully fledging, juveniles wander off to the fringes of the colony where they practice hop-flying, but return to their nests to be fed, and most prefer to walk to the shore and swim rather than follow the adults into flight. This stage is fraught with dangers, such as falling victim to predation by seals. These birds fledge with a store of fat that enables them to survive without food for up to ten days, during which time they must learn the essential skills of capturing sufficient food for survival. The mortality rate for the Cape gannet is at its highest during this precarious stage of life (4).

The Cape gannet hunts for fish with spectacular power, grace and precision, plunge-diving for prey from heights of 10 to 30 m with flexed wings, pointed tail and feet, and total focus on its quarry. Just before entering the water, the bird stretches and swings its wings backwards to form a streamlined arrowhead-like body as it pierces the water (4). Surprised fish are caught in the bird’s dagger-like bill and may be swallowed before even leaving the water (5) (7). Shoaling fish in surface waters are preferred, including anchovy (Engraulis capensis), sardine (Sardinops sagax) and saury (Scomberesox saurus), and offal discarded by fishing boats may also be taken (2) (5).

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Cape gannet range

Breeding occurs at six offshore islands, three of which (Mercury, Ichaboe and Possession) are off the Namibian coast, two (Bird Island, Lambert's Bay; Malgas Island, Saldanha Bay) off the west coast of South Africa, and one (Bird Island, Port Elizabeth) off the east coast of South Africa (2) (4). The Cape gannet’s wintering, non-breeding range is restricted to the coast of Africa, where adults are fairly sedentary, but young range east to Mozambique and Tanzania, and regularly north as far as Nigeria (2).

See this species on Google Earth.

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Cape gannet habitat

Breeding takes place in densely packed colonies either on the flat ground of the low lying islands, or on flat ledges of the steeply sloping Mercury Island (4). Nests are a mound of the birds’ droppings, guano, in which other material such as feathers and bones may be mixed (3) (5) (8). The wintering range is typically confined to the continental shelf, at no more than 100 km from the coast, although birds have occasionally been recorded on oceanic waters (4).

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Cape gannet status

Classified as Vulnerable (VU) on the IUCN Red List 2006 (1).

IUCN Red List species status – Vulnerable

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Cape gannet threats

With breeding restricted to just six small islands, the Cape gannet is considered vulnerable due to over-exploitation of its prey by human fisheries, pollution, and human disturbance (2). Food shortages, following the collapse of the Namibian sardine fishery, have been the main cause of the 85 to 98% decline in numbers seen at the three Namibian colonies over the past 50 years (1956 - 2006) (2) (9). By contrast, increases were seen at all three South African colonies during this time, until December 2005, when attacks by Cape fur seals (Arctocephalus pusillus) on birds at nests at Lambert’s Bay caused abandonment of the entire 20,000-strong colony (9) (10). Oil spills are also a significant threat, with around 5,000 Cape gannets found oiled during an incident in 1993 (2). Additionally, although information of other pollutants affecting Cape gannets has been scarce, traces of DDE, DDT, Dieldrin and PBC's have been found on eggs (4). Guano was collected at all Cape gannet colonies to be utilised for fertiliser, and may have decreased breeding success through inhibiting some birds from laying and reducing the effective breeding season (2) (4) (8). Mortality of Cape gannets occurs from drowning in long-line fisheries (7).

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Cape gannet conservation

All breeding colonies of the Cape gannet are under some form of protection (4). In South Africa, all colonies are under the administration of CapeNature Conservation (Bird Island, Lambert's Bay) or South African National Parks (Malgas Island; Bird Island, Port Elizabeth) (2) (4) (8). In Namibia, the three breeding islands are administered by the Ministry of Fisheries and Marine Resources. All six islands have been identified as Important Bird Areas (IBAs) (2) and public access is restricted, with the exceptions of Bird Island (Lambert's Bay), where visitors are able to view the colony from state-of-the-art observation facilities, and Malgas Island, to which guided tours organised by the West Coast National Park are available (4). Oiled birds are rehabilitated at the South African National Foundation for the Conservation of Coastal Birds (SANCCOB) (4), and the species is protected by law (2).

Following the colony’s abandonment of Bird Island, Lambert’s Bay, in December 2005, and the consequent collapse of a profitable bird-watching industry there, an ingenious plan to entice the birds back was quickly formed. Duck hunters have long known that carved wooden ducks floating on the water will attract the real thing, so a similar tactic was employed using life-sized gannet ‘decoys’ to tempt the real birds back. These fake birds were deployed on the deserted nests early in July 2006 after the provincial nature conservation authority, CapeNature, had appointed an island manager, Yves Chesselet, who is working on plans to protect the gannets from the seals. The initiative has been a fantastic conservation success story, with gannets starting to land within an hour of putting out the decoys, and nearly 10,000 having returned by mid-August (10). A largely successful programme to discourage seals on Mercury Island could perhaps now be employed to similar effect on Bird Island (2).

View information on this species at the UNEP World Conservation Monitoring Centre.
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Find out more

For more information on the Cape gannet see:

For more information on this and other bird species please see:

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Authentication

Authenticated (05/12/2006) by Dr. Robert Crawford, Marine and Coastal Management, South Africa's Department of Environmental Affairs and Tourism,
http://web.uct.ac.za/depts/stats/adu/staff/ps_rob.htm


http://www.mcm-deat.gov.za/

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Glossary

Primaries
In birds, the main flight feathers projecting along the outer edge of the wing.
Secondaries
In birds, the shorter flight feathers projecting along the inner edge of the wing.
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References

  1. IUCN Red List (September, 2006)
    http://www.iucnredlist.org
  2. BirdLife International (November, 2006)
    http://www.birdlife.org/datazone/species/index.html?action=SpcHTMDetails.asp&sid=3653&m=0
  3. del Hoyo, J., Elliott, A. and Sargatal, J. (1992) Handbook of the Birds of the World – Ostrich to Ducks. Vol. 1. Lynx Edicions, Barcelona.
  4. Navarro, R. Cape Gannet Morus capensis. University of Cape Town: Avian Demography Unit (November, 2006)
    http://web.uct.ac.za/depts/stats/adu/species/sp053_00.htm
  5. KidsBiology.com (November, 2006)
    http://www.kidsbiology.com/animals-for-children.php?animal=Cape%20Gannet
  6. Siyabona Africa: Timbavati Private Game Reserve (November, 2006)
    http://timbavati.krugerpark.co.za/africa_cape_gannet.html
  7. Crawford, R.J.M. (2005) Cape Gannet. In: Hockey, P.A.R., Dean, W.R.J., Ryan, P.G. and Maree, S. (Eds) Roberts Birds of Southern Africa, 7th Edition. John Voelcker Bird Book Fund, Cape Town.
  8. Crawford, R.J.M. (2006) Pers. comm.
  9. Crawford, R.J.M., Dundee, B.L., Dyer, B.M., Klages, N.T., Meÿer, M.A. and Upfold, L. (2007) Trends in numbers of Cape gannets (Morus capensis), 1956/57-2005/06, with a consideration of the influence of food and other factors. ICES Journal of Marine Science, 64. Available at:
    http://icesjms.oxfordjournals.org/cgi/content/abstract/fsl011v1
  10. Ferreira, A. (27th August 2006) Decoys save Lamberts Bay after seal bloodbath. Mail and Guardian Online (November, 2006)
    http://www.mg.co.za/articlePage.aspx?articleid=282102&area=/breaking_news/breaking_news__national/
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Image credit

Cape gannet in flight, preparing to land  
Cape gannet in flight, preparing to land

© Ingrid van den Berg / www.ardea.com

Ardea wildlife pets environment
59 Tranquil Vale
London
SE3 0BS
United Kingdom
Tel: +44 (0) 208 318 1401
ardea@ardea.co.uk
http://www.ardea.com

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