Colours of Wildlife: Cape Gannet
Created | Updated Jun 30, 2019
Cape Gannet
Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"
Here is a painting of some Cape Gannets, Morus capensis. The scientific name means 'fool from the Cape'. The name 'gannet' comes from an old word which also is the root of the modern word 'gander'; the term 'gannet' is sometimes used for a gluttonous person. In Afrikaans it is called a 'Malgas' which is a contraction of 'mal gans' which means 'crazy goose'. Gannets form a family with the somewhat unfortunately-named Boobies. That word in the olden days referred to a stupid person. Most boobies nest on islands where they historically never encountered predators; when humans reached the islands, these birds were totally fearless of them and thus got very easily captured, hence the name. Gannets are similarly foolishly-fearless in their nesting colonies.
Gannets and boobies are very similar in outward appearance. They're large birds with compact, bullet-shaped bodies, rather long necks, and stout bills with a sharp hook at the tip. Their feet have all four toes connected with webbing. Boobies are somewhat smaller than gannets, and sometimes have brightly coloured faces and/or feet. Boobies occur more in the tropics, while gannets roam the colder waters both in the north and in the south. There are three species of gannet: the Atlantic Gannet lives in the north Atlantic with colonies around both Canada and Europe; the Australasian Gannet lives around Australia with most nesting colonies in and around New Zealand; the Cape Gannet breeds just off the southwestern coast of Africa, in the countries of South Africa and Namibia. At present, there are no gannets in the north Pacific Ocean, but in prehistory species existed there and also around the western coast of South America.
The Cape Gannet is a very handsome bird with its delicately golden-coloured head and neck and the bold lines of 'make-up' on its face and throat. It reaches a head-to-tail length of 94 cm/37", a wingspan of 1.8m/6' and a weight of 2.7 kg/6 lb. It has long, black-edged wings and a black-tipped tail.
Air Bags Included
Gannets are hunting birds of the oceans. They fly out over the sea, sometimes as much as 100 km/62 miles from the coast, hovering at an altitude of between 3 and 30m/10' and 100', peering down with their keen eyes for fish. Having spotted one, a gannet will dive down to catch it. It uses a technique of folding its wings back and plummeting down like a rocket. Its face and body are padded by literal air bags, sacs which are extensions of its breathing system. All birds have these air sacs throughout their bodies; they're all connected with the lungs and enable birds to breathe with the air constantly flowing through their lungs. This improves their oxygen intake to provide them with fast energy during flight. In the gannet's case the air-bags act like pads or cushions breaking the shock from the gannet hitting the water at up to 120 km/h or 75 mph.
In addition, a gannet's nostrils don't open to the outside, so that sea water wouldn't be forced into its airways when it hits the water. Its eyes, too, are protected by thick lids as well as a third 'lid' called a nictitating membrane. Its bill has serrations or 'teeth' at the front to help it catch and hold on to fish.
The momentum gained from a plummet can take a gannet as much as 11 m/36' below the sea surface. Sometimes it uses its webbed feet to propel it down even deeper, up to 25m/80'. It has dense, waterproof feathers, which together make it very buoyant so that it rises to the surface naturally. If successful, it will swallow its fish before rising to the surface. It can swallow a fish up to 40 cm/16" in length, and can gorge itself with up to 1 kg of fish at a time. But gannets can also survive for several days without eating, should the fishing not go well. Gannets store quite a lot of fat in their bodies, which not only gives them some energy reserves in case of food scarcity, but also helps insulate them in cold water.
Gannets mostly hunt on the wing, in large groups. They prefer fish that form big shoals, such as sardines. Their white plumage makes the gannets visible from far off; this means that gannets can see each other and when one spots a shoal and starts diving, other gannets immediately see it and fly to the same spot to target the same shoal. When lots of gannets dive at the same time, the fish are confused and find it hard to escape.
Human fisherfolks have also learnt the trick of using gannets to find big shoals of fish. This had the unfortunate consequence that the gannets' main food supply has been greatly reduced, at least in the Namibian part of the range. Luckily the gannets in the South African part of their range actually seem to be increasing their numbers.
Nests of Guano
Gannets are most easily spotted at their breeding colonies, which are situated on islands just off the coast, where they're safe from land predators. They breed in large numbers, with their nest spaced about the length of an adult gannet apart. The nests are made of the parents' own guano (i.e. droppings)!
Especially in the western breeding islands, where rainfall is very low, the guano had accumulated to great thicknesses on the gannet islands. During the mid-nineteenth century there was a scramble for guano (it's an excellent natural fertilizer), and very large amounts of it was removed. This actually endangered the gannets; the excesses were soon stopped by the gannet islands being given official protection. Today a small amount of guano (about 4000 tons) is harvested each year; this is a sustainable level that doesn't harm the breeding birds.
The painting shows two gannets greeting each other. Gannets form monogamous pairs that stay together for many breeding seasons or for their entire adult lives. They retain the same nest in the colony for as long as they breed. Each season a female gannet lays just a single egg. She and her male share incubation duties. They fold their big, webbed feet over the egg to keep it warm. When the chick hatches, they may also warm it with their feet in the same way. The parents share incubation and chick brooding duties; there will always be one parent on the nest while the other is out finding food. The greeting displays happen when the parent that was out, returns to the nest. The returning male will lightly bite the female, then the two of them will 'fence' with their bills. They also preen each other. The two birds stretch out their necks upward and lightly tap their bills together, as seen in the painting; then they bow their heads down. When walking through a colony, a bird will keep its bill pointing straight up, as if to show it has no interest in disturbing the nesting birds around it. They, in turn, will let it alone. But sometimes gannets are aggressive to each other, especially if their nests are close together. They may threaten their neighbours and jab at them with their bills, and sometimes they fight. Gannets are noisy in their colonies, uttering raucus 'harra-harra'-calls. Couples can recognize each other and also their chicks by these calls.
Chicks fledge at an age of about 100 days. Immatures are brown with white spots, which increase over time until the adult white plumage is attained. The young birds may spend a couple of years at sea before coming back to land to start their own breeding attempts. Young birds sometimes fly far away from the breeding grounds. Vagrants have been recorded off tropical West Africa, Madagascar, at the sub-Antarctic Amsterdam Island and even mixed in with Australasian gannets in Victoria, Australia.
Gannets do suffer natural predation. They are occasionally caught at sea, while swimming or diving, by seals or sharks. Seals also sometimes displace them from their colonies. Gulls occasionally prey on their eggs. As noted, gannets sometimes suffer from their fish stocks being depleted by humans. Nevertheless, the Cape Gannet still has a world population of over 300 000 birds. The largest colony is of 140 000 birds at Malgas Island. While not completely safe, it is not threatened with immediate extinction.
