Swift Tern Sterna bergii

Janine le Roux

Avian Demography Unit, Dept of Statistical Sciences, University of Cape Town, Rondebosch, 7701, South Africa

Photo: H.D.Oschadleus This Swift Tern was trapped on Robben Island on 3 May 2002. A metal ring was placed on the right leg, a red engraved Pro-Touch band on the left leg and the bird was marked with yellow picric dye to facilitate observations.

The Swift Tern, also known as the Greater Crested Tern, is found on coastlines in the south-east Atlantic Ocean, the Indian Ocean and the western Pacific Ocean. In southern Africa, Swift Terns are a common resident, found on marine shores and estuaries. There are approximatley 6000 breeding pairs, although the number breeding from year to year does vary. The non-breeding distribution extends from Luanda, Angola, to Kosi Bay, KwaZulu-Natal, South Africa. However breeding has been restricted to 27 identified localities between Swakopmund in Namibia to Stag Island, Algoa Bay, South Africa.

Usually only six to seven of the known breeding localities will be occupied in one breeding season. These are usually areas found between Saldhana Bay and Cape Town, indicating that 80% of the breeding takes place within the Benguela upwelling ecosystem. Swift Terns are nomadic between these different breeding sites and breeding usually peaks in February and March in the Western Cape. This is the late summer, early autumn period and most young have fledged by April and May.

Photo: Kathy Calf Recently hatched Swift Tern chick. Photo taken at Robben Island on 3 May 2002.

Swift Terns breed in colonies, usually on protected islands, and often in association with Hartlaub's Gulls. The nests are shallow scrapes, and usually on open flat ground. Egg laying is synchronised within the Swift Tern breeding groups, with one or two eggs per clutch. Incubation time is 28 days. Chicks remain in the nest for about four days, and can fly within two months. Most fledgling leave the colony with at least one parent and within 19 days of fledging. The majority of Swift Terns move up the east coast with their juveniles, towards KwaZulu-Natal, and some move up into Namibia. It has not as yet been determined if these juveniles are moving into nursery areas.

During the breeding season fish form 86% of all prey items taken; 60% of this pelagic shoaling fish of which the Cape Anchovy is the most abundant. Prey size taken to chicks can vary from 7 mm to 138 mm in length and from 0.1 g to 30 g in mass. Kelp Gulls, Hartlaub's Gulls and Sacred Ibises have been observed feeding on the eggs or nestlings of Swift Terns, particularly as a result of disturbance. Parental recognition of chicks takes place by means of a 'kurriet call' when visual contact is not possible.

Photo: Kathy Calf Colony of Swift Terns and Hartlaub's Gulls breeding on Robben Island. Taken in April 2002.

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