Adult raptors have few predators and may live for 20 to 30 years. In common with other long-lived species, raptors have a slow breeding rate and a high mortality among young birds. Approximately one-quarter of raptors survive their first year, and only half of these will reach maturity and raise their own young. When adult survival drops as a result of poisoning and hunting, the population of the affected species will be drastically reduced.
Some poisons, such as organochlorine pesticides, build up in a food chain. A raptor's position at the end of the food chain makes it particularly vulnerable to receiving a large dose. Thus raptors that eat poisoned prey may die, or become unable to breed. Fortunately persistent organochlorines have been banned in South Africa.
Owls may be paralysed or killed after eating rodents poisoned by certain rodenticides. Poisoned rats and mice, whether dead or moving slowly as a result of being poisoned, are easier for owls to catch. Thus owls will eat more of these, and accumulate a large dose of poison.
Fenthion (used to kill quelea) has, in the past, been incorrectly applied and resulted in widespread deaths of non-target species such as birds of prey and herons. Gamma-BHC was, until recently, used for locust control, and may have contributed to a decline in raptor numbers. It has been replaced by pyrethroid products.
With the spread of modern farming, domestic stock replaced herds of game, and their predators, including hyaenas, were eradicated. Vulture numbers dropped as a result of fewer carcasses being available. Without hyaenas to break up the bones of a carcass, there were no calcium rich bone chips for adult vultures to feed their young. Young vultures thus developed a calcium deficiency which resulted in malformed wings making them unable to fly.
The illegal practice of egg-collecting has made more of an impact on birds of prey in Europe than in southern Africa. Local species which could be affected by egg-collectors include the very rare taita falcon, found in Zimbabwe, the booted eagle, black eagle, Cape vulture and black sparrowhawk.
On rare occasions, raptors collide with electricity conductors or the guy wires of telecommunication towers (as used by Telkom and SABC). This is most common amongst young birds learning to fly, or in areas which attract a concentration of birds, such as wetlands.
Eskom has addressed these problems by developing insulators and perches to reduce the electrocution threat, markers to reduce collisions, and nesting platforms and insulator shields to protect the electricity supply.
* Nature conservators can also support farmers in identifying and preserving raptor habitat, and in running a `vulture restaurant'!
* Use rodenticides, such as "Racumin", that will not kill owls.
* Prevent disturbance of roost and nest sites.
EAGLES AND FARMERS. Endangered Wildlife Trust and SA Ornithological Society, Johannesburg, 1988.
PREDATORS AND FARMERS. A. Bowland, M. Mills and D. Lawson. Endangered Wildlife Trust, Johannesburg, 1993.
POPULATION ECOLOGY OF RAPTORS. I.Newton, T. & A. Poyser. Calton, UK, 1979.
BIRDS OF PREY OF SOUTHERN AFRICA. P. Steyn. David Philip, Cape Town, 1982.
BIRDS OF PREY. I. Sinclair and D. Goode. Struik Pocket Guides for Southern Africa, 1986.
THE VULTURES OF AFRICA. P. Mundy, D. Butchart, J. Ledger and S. Piper. Acorn Books and Russel Friedman Books, Johannesburg, 1992.
All books are available from Russel Friedman Books, PO Box 73, Halfway House 1685. Tel. 011-7022300/1.
Enviro facts: "Farmers, poisons and wildlife", "Poisons in the home and garden".
Vulture Study Group. PO Box 72334, Parkview, 2122. Tel. 011-646 8617.
Poison Working Group. PO Box 15121, Lynne East, 0039. Tel. 012-808 0592.
Animal Rehabilitation Centre. PO Box 15121, Lynne East, Pretoria, 0039. Tel. 012-808 1106. Treat and care for poisoned animals.
AVCASA. Agricultural and Veterinary Chemicals Association of South Africa. PO Box 1995, Midrand, 1685. Tel. 011-805 2000.
Southern African Ornithological Society. Head Office P O Box 87234 Houghton, Transvaal, 2041 Tel. 011-888 4147
Provincial conservation authorities. See telephone book for details.