Kelp Gull (Larus Dominicanus Vetula) "Cape Gull"
Les Underhill and John Cooper
Animal Demography Unit
Photo Les Underhill
Adult Kelp Gull sporting the engraved colour-ring AJ
The nominate race of the Kelp Gull Larus dominicanus dominicanus occurs along the coasts of South America, New Zealand, Australia and many islands in the Southern Ocean. The subspecies found along the southern African coastline, L. d. vetula, is currently thought to be sufficiently different from the nominate race that it ought to be regarded as a full species. The proposed English name is "Cape Gull".
Kelp Gulls breed in Namibia and South Africa; there are large colonies between Cape Cross and the islands in Algoa Bay, with occasional nests recorded as far north as Cape Fria and as far east as the Great Fish River. Along the west coast, nonbreeding birds occur north to Luanda, Angola, and along the east coast as far as the Limpopo River mouth in Mozambique. Apart from around the Greater Cape Town area, Kelp Gulls seldom occur more than a few kilometres inland. Records of black-backed gulls in the interior of southern Africa, and along the coastline of northern Mozambique, are far more likely to be Lesser Blackbacked Gulls L. fuscus from the Palearctic than Kelp Gulls.
The southern African population of Kelp Gulls has been estimated to contain 11 000 pairs, 9000 in South Africa and 2000 in Namibia. Even though the total population of Kelp Gulls (treating it as the species L. vetula) is far smaller than that of African Penguins Spheniscus demersus, which contains about 180 000 birds, it is not regarded as threatened. This is because the penguin population is steadily decreasing at a rate of about 2% per year, while that of Kelp Gull is on the increase.
Photo Les Underhill
Kelp Gull with chick, Lamberts Bay, November 1998
This upwards trend is in part due to the suspension of persecution by humans. Numbers on the guano islands were controlled in order to reduce predation on the main guano-producing birds. The main factor in the increase in Kelp Gull populations has been human subsidies: large numbers take discards of fish behind trawlers and at fish processing factories; even larger numbers occur at rubbish tips, where they feed on discarded food. For example, the rubbish dump near the Strandfontein Sewage Works on the Cape Flats, regular supports more than 1000 Kelp Gulls, the largest known concentration of the species outside a breeding colony.
Kelp Gulls are aggressive predators on the offshore islands. They take every conceivable opportunity to rob African Penguins, Cape Gannets Morus capensis, cormorants, terns and Hartlaub's Gulls L. hartlaubii of their eggs and small nestlings. The two species for which they cause the most serious problems, from a conservation perspective, are the penguin and the Roseate Tern Sterna dougallii.
The complete removal of thick layers of guano from the offshore islands during the "white gold rush" of the 19th century means that many penguins are forced to nest on the surface, rather than in burrows. These surface nests are extremely vulnerable to predation by Kelp Gulls; 40 days of continuous vigilance are required to hatch a penguin egg, and it is many weeks before the chick is large enough to fend off an attacking Kelp Gull.
Roseate Terns are particularly sensitive to disturbance, leave their nests readily at the approach of any perceived danger, and take a long time to return. Kelp Gulls are abundant on the three islands where this species currently breeds (Dyer Island, St Croix Island and Bird Island, Algoa Bay), and take a heavy toll on the nests of Roseate Terns.
Kelp Gulls don't have things all their own way, however. The White Pelicans Pelecanus onocrotalus on Dassen Island have, over the past few years, taken to eating Kelp Gull chicks, and have reduced the breeding productivity on this island to very low levels.
Most ringing of Kelp Gulls is of nestlings. Young birds frequently move considerable distances in the first year after fledging. An extreme example of this is of a nestling ringed on Schaapen Island in Langebaan Lagoon; it was recovered four months later 1211 km farther north close to Swakopmund in Namibia. However, most Kelp Gulls ultimately return to their natal colonies. There are exceptions; a nestling ringed on Stag Island, Algoa Bay, was recovered 10 years later in Swakopmund. There are three records of nestlings living to ages exceeding 20 years. The oldest bird was ringed in November 1971 in the colony near Plettenburg Bay; it was recovered just over 24 years later, in January 1996, very close to the place where it had been ringed.
Kelp Gulls are one of the species being targetted with individually engraved colour rings. We are doing this to determine their movement patterns. If you see one of these birds, please report the colours and the letters/numbers to SAFRING. The instructions on what to report are on this website.
Photo Les Underhill
Adult Kelp Gull