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Hartlaub's Gull

The Year 2000 Breeding Season

Although substantial flocks of Hartlaub's Gulls gathered on Robben Island in the first four months of the year, no breeding was observed. This had been the main breeding colony in autumn and winter 1999; in 1998 they had bred in Cape Town harbour. The return to Robben Island was thought to be related to an intensive effort to remove feral cats from the island in 1998. However, control efforts had been relaxed, and the failure to breed on Robben Island in 2000 is possibly related to an increase in the numbers of cats on the island.

The location of the breeding colony in the Cape Town area was unknown until James Harrison and Doug Harebottle (Animal Demography Unit) discovered them breeding on an island in the retention dam at Century City during the monthly bird monitoring conducted there by the ADU. Century City is a massive development immediately north of the N1 about 7 km from Cape Town. The retention dam is not to be confused with the "wetland reserve", which was featured in the February-March 2000 edition (Volume 5, Number 1) of Africa – Birds & Birding. If you have a copy of that article, then the retention dam and its island is clerly visible in the top centre of the aerial photograph spanning most of pp 44 and 45. There is no public access to the retention dam.

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

Leisha Upfold (Marine and Coastal Management, Department of Environmental Affairs and Tourism) and Les Underhill (Animal Demography Unit) obtained permission from the developers to survey the island on 12 May 2000. Leisha counted nearly 1200 nests, and there were already a couple of hundred "runners" (chicks old enough to leave their nests). 40 large runners were ringed with both metal and engraved plastic rings. One dead bird with a ring was found, lying at the water's edge on the island. It had been ringed as a chick on 2 July 1998 at Cape Town Harbour, and was therefore in its second year, the earliest age at which Hartlaub's Gulls breed. We do not know if this bird was actually engaged in breeding, or whether it was visiting (or "prospecting") the colony.

One week later, on 19 May, a joint ADU-MCM party of five researchers revisited the island, and ringed 15 adults and 62 runners. Nine resightings were made of birds ringed elsewhere. Seven were birds that had bred on Robben Island in 1999 – these birds were among a handful of adults which had been mistnetted in 1999 near breeding colony on the island, and fitted with colour rings during the pilot phase of this project. This is probably the first proven movement of individual birds between different breeding colonies in successive years. Two of the birds resighted had been ringed as nestlings on Robben Island. One had been ringed on 11 May 1974, and is now the oldest Hartlaub's Gull on record – 26 years and 9 days since ringing. The other had been ringed on 15 May 1974, 24 years and 4 days previously. This is the third oldest Hartlaub's Gull. The second oldest was ringed on Robben Island in 1975, and was retrapped a few months ago at the Paarl Sewage Works.

Ringed adult
Photo L. G. Underhill

On 26 May, 42 runners and 12 adults were ringed. Six adults which had been ringed last breeding season on Robben Island were resighted, one of which was seen sitting on a nest with two eggs.

Hartlaub's Gull Nest
Photo L. G. Underhill

Many runners are now fliers, and we look forward to finding out where they have moved to! Please inspect all the Hartlaub's Gulls you see for rings. The yellow colour ring is conspicuous. It has two letters or digits engraved in black. Unless the bird is extremely close, you will need binoculars or a telescope to read the characters. Binoculars are fine up to a distance of about 20 m. If you are 100% sure that you have read the ring correctly, please report the sighting to SAFRING. The email address is safring@adu.uct.ac.za, the phone number is (021) 650 2421, and the fax number is (021) 650 3434. The information needed is date, time, place, and the band number. Please send your address and contact details. SAFRING will let you know where the bird was ringed, and if it has been seen by anyone else.