Cape Gannet (Morus capensis)

[order] SULIFORMES | [family] Sulidae | [latin] Morus capensis | [UK] Cape Gannet | [FR] Fou du Cap | [DE] Kaptolpel | [ES] Alcatraz del Cabo | [NL] Kaapse Jan van Gent

Subspecies

Physical charateristics

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. 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. There are also distinctive black lines around the beak and on the face. The powerful, pale blue bill is pointed with fine serrations near the tip, and the large feet are webbed between each toe. Juveniles are dark brown, and gradually gain increasing amounts of the white feathers of the adult plumage after their first year.

Listen to the sound of Cape Gannet

[audio:http://www.aviflevoland.nl/sounddb/C/Cape Gannet.mp3]

Copyright remark: Most sounds derived from xeno-canto

Range

Africa : South coasts

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. Nests are a mound of the birds’ droppings, guano, in which other material such as feathers and bones may be mixed. 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.

Reproduction

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. 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. 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.

Feeding habits

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. Surprised fish are caught in the bird’s dagger-like bill and may be swallowed before even leaving the water. 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.

Conservation

This species is listed as Vulnerable since it has a very small breeding range on just six islands, and over-exploitation of its prey by human fisheries – compounded by pollution – is causing a continuous decline in the quality of surrounding waters for foraging.
Morus capensis breeds at just six islands: Bird (Lambert’s Bay), Malgas and Bird (Algoa Bay), South Africa, and Mercury, Ichaboe and Possession, Namibia. Historically it bred on four more islands3. Outside the breeding season, adults are generally sedentary but young range east to Mozambique and Tanzania, and regularly north as far as Nigeria, but usually within 100 km of land. In 1996, the global population numbered c.173,000 breeding pairs: 153,000 (88.4%) in South Africa, the balance in Namibia. The total breeding population in 2004-2006 was c.150,000 pairs3. Exchange occurs between breeding localities. Although the numbers breeding at South African islands increased between 1956 and 1996, the Namibian population declined massively. The total breeding population has decreased by 1.14% per year over the 49 years between 1956-1957 and 2005-2006, equivalent to 36% over 39 years3. The colony at Possession Island now numbers only 750 pairs, and may soon be lost.

Migration

Adults range little from colony after breeding, most staying in adjacent waters. Young birds migrate N to Gulf of Guinea, also a few off Mozambique. May occur irregularly in European waters.

Distribution map