The Cape Bird Club

Western Cape Raptor Research Programme Anthony van Zyl.

Anthony's interest in raptors started in the Eastern Cape where he grew up. At school he started plotting all the Black Eagle nests in the district and measure internest distances to predict where other nests could be. He completed a Zoology degree in Pretoria and was mentored by Dr Alan Kemp at the Transvaal Museum. He did his Honours at Rhodes and Masters at UCT. His Masters thesis was on the ecology of the Rock Kestrel, and is still the subject of his passionate interest. He first worked for the Transvaal Museum, as a Curator in the Bird Department, before moving to Cape Town to take up a position in the computer industry. He now persues his raptor interests part time.

Anthony is continuing with the work he started in his Masters thesis. He monitors Rock Kestrel nests around Cape Town, of which approximately 44 are found on the mountainous areas of Table Mountain, down to Cape Point. Then one still needs to consider that Rock Kestrels breed all over buildings and in some cases cranes! Old records from previous years identify Fish Hoek Hospital, Groote Schuur, Tygerberg Hospital and Tafelsig Flats in Bellville as sites where Rock Kestrels have had their nests. Anthony has just had a call from a friend who works in Sea Point to say that there are 3 Rock Kestrel chicks begging on their company balcony. There is also a pair breeding on a building next to Anthony's work in Montague Gardens. This current breeding season, has led to the discovery of a Rock Kestrel nest on the Reeds Delta building on the Foreshore in Cape Town. A resident caretaker in one of the taller buildings in the area maintains they have been breeding there for 4 years! This nest produced 4 chicks, 3 fledged successfully and have been seen perching on the Artscape Theatre building patiently waiting for their next meal. The 4th unfortunately met an untimely death at the careless wheel of a vehicle on Hertzog Boulevard.

photograph by Andrew Jenkins

Anthony absieling down a rock face to a nest site.

Rock Kestrels love the quarries around Durbanville and up the west coast where they nest in semi colonial circumstances, with one quarry housing 12 pairs of nesting kestrels. Some nests are as close as 3 meters apart. In one quarry Anthony found a pair nesting in a rock pile on the ground. Because of a lack of time, Anthony limits his specific study area from the Muizenberg/Steenberg ridge in Silvermine, down south to Cape Point. In this area there are about 15 pairs and they all nest on cliffs or in quarries. It is interesting to note that during one of his studies in the Eastern Cape, Anthony found that about half the population nested away from cliffs in old stick nests in trees. He has yet to find a tree nest in the Cape Town surrounds. (Perhaps something volunteers could look out for!)
He collects very basic information, but in the long term this can tell one a lot about factors affecting Rock Kestrel productivity. This information is useful when evaluating aspects of alien vegetation management, such as clearing and the use of fire. It also shows how birds adapt to different environments in the long term and the effects of climate change.
An exciting part of Anthony's project is to one day be able to monitor the factors contributing to the breeding success of the Rock Kestrel population, and then be able to predict how the season is going to turn out. It already seems as though Rock Kestrels are more successful if they can feed on rodents, rather than lizards, during the breeding season. Weather is a factor too. Heavy rain when they have eggs, can have a direct impact on their ability to incubate. It has been shown that the onset of the breeding season in kestrels is triggered by day length. Then the number of eggs laid, is triggered by the amount of food the male can provide for the female. So if the Cape Town climate is changing as it appears to be, with winter hanging in later each year, this could have an effect on the kestrel population in the long term, because they will want to breed, (days getting longer), while the food supply is not as good as it should be, because of the wet weather.

photograph by Andrew Jenkins

A Rock Kestrel.

As with most raptors, anecdotes abound. There is a record on one pair nesting in a braai. Another nesting at the Athlone Power Station, used the window when flying to the nest and the door when they were leaving! Yet another pair used to catch pigeons at night in a hangar at the airport. A tragic incident where people failed to notice that Rock Kestrels were breeding in a building, locked them out and all but one chick starved to death! The remaining chick was taken to a rehabilitation centre, but was unable to grow healthy feathers and as a result probably did not live long.

photograph by Anthony van Zyl

The Rock Kestrels are being watched in April 2005!!

For the last two years Anthony has been looking for a Rock Kestrel nest on Steenberg ridge. He knew there had to be one because he discovered, recently fledged chicks, on the ridge the year before. Last weekend he found the nest! (Nov 2004 - See the picture on the main page). In a crack, right in the middle of a well frequented climbing route. He had been concentrating on the less busy areas of the ridge, only to find that the Rock Kestrels had got so used to people, they must have been incubating their eggs with climbers sliding right past them. Although human disturbance has not prevented them from breeding, there were only 2 chicks this year, which is the smallest brood for the Peninsula on record this year. (photo) Having people on the cliff definitely prevents the adults from bringing in food, but maybe because climbing mostly happens on good weather weekends, it did not affect them too much??

Anthony van Zyl, 

See Anthony's web site on Kestrels  (Feb 2005)


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