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Hartlaub's Gull

Press Release 15 May 2000

Hartlaub's Gulls Larus hartlaubii colony at Century City

Press release 15 May 2000

The floodwater retention dam at Century City is currently vibrant with activity. Hartlaub's Gulls have moved in and are breeding in large numbers. Such big colonies are usually found on the offshore islands. Now they are breeding on the island in the dam.

Breeding colonies of Hartlaub's Gulls have been very mobile in the past few years. In the 1970s and 1980s, most bred on Robben Island. Robben Island has had a feral cat problem, and they stopped breeding there. In recent years, the gulls have moved around between several sites. Most cats were removed from Robben Island two years ago, and large numbers of gulls bred there throughout autumn and winter 1999.

When they breed on Robben Island, the gulls fly to the mainland to find food for their chicks. The round trip is about 24 km. So they can be forgiven if they find a breeding site closer to food supplies. The island in the retention dam is eminently suitable, a safe place free of predators and with little disturbance. This is the only place in the Greater Cape Town area where Hartlaub's Gulls are known to be breeding in large numbers this year.

Ms Leisha Upfold, of Marine and Coastal Management, and Professor Les Underhill, Director of the Avian Demography Unit at UCT, did a survey of the gull colony on 12 May 2000. They counted 1200 nests with eggs and tiny chicks; in addition, there were 200 "runners" (chicks that had left the nest), and some of these young birds were already able to get airborne. They ringed 40 chicks with metal rings and with plastic rings. The plastic rings are bright yellow, and have two letters and numbers inscribed on them in black. If you are lucky enough to read one of these yellow rings, please report this to SAFRING at UCT – 650 2421 or safring@adu.uct.ac.za and provide the inscription, date, time and place.

Although Hartlaub's Gulls appear to be extremely abundant birds to anyone living in Cape Town, this is not actually true. There are 50 species of seagulls in the world. Our Hartlaub's Gull is the 10th rarest. The best estimate of the total population size of Hartlaub's Gull is 30 000 birds, and virtually all are found between Cape Agulhas and Swakopmund. The birds breeding at Century City are probably 10% of the world population. Because the species usually breeds at only one site near Cape Town each year, this colony should be given special protection; if it fails, a year's breeding productivity will be lost. These birds literally do put all their eggs in one basket!

Two views of the breeding colony in the retention dam at Century City.
Breeding colony in the retention dam at Century City
Breeding colony in the retention dam at Century City
Photos L. G. Underhill