Farming, Poisons and Wildlife

Agricultural use of chemicals such as pesticides and poisons poses extremely serious threats to wildlife and people.

Farmers use a wide range of chemicals to protect crops from insects and disease, to control ticks and other parasites, and to kill predators such as jackal and caracal. Government agencies use pesticides to combat locusts, malaria-carrying mosquitoes, tsetse flies and queleas.


PESTICIDES

Organochlorines: Of all the pesticides ever used, the organochlorines have done the most harm to wildlife. These include DDT, aldrin, dieldrin, endrin,endosulphan and gamma-BHC. Besides being toxic, organochlorines have various properties which make them harmful to wildlife. For example, they are extremely stable and remain unchanged in the environment for many years. In addition, they are stored and accumulate in the fat of animals, and thus pass from prey to predator, concentrating at successive steps in a food chain. Animals at the end of food chains, such as birds of prey, are especially likely to accumulate large amounts of poison.

As the side effects of organochlorines became known in the 1960s, most nations placed restrictions on their use. In South Africa and Namibia, DDT, widely applied from 1946, was prohibited in agriculture and is now used only by government for malaria mosquito control. Manufacture of these chemicals continues, however, and the main market has shifted from developed to developing countries. Zimbabwe, for example, imported 1000 tonnes of DDT in 1982.

Organophosphates: These have largely replaced organochlorines in agricultural pest control. They are thought to be safer than organochlorines as they break down more rapidly. Organophosphates are responsible for most acute pesticide related poisonings amongst humans. In 1985, organophosphate poisonings were the second most common reason for Tygerberg Hospital's ICU admissions. Carbamates and Pyrethroids: These modern insecticides are usually not toxic to mammals, but are extremely toxic to birds. Carbamates are used in termite control and this can reasult in the secondary poisoning of birds that have eaten poisoned termites.

Pesticides play an important role in the control of human and animal diseases, and crop pests. However, the continued use of organochlorines, for example, could seriously damage fish and wildlife resources as well as pose a health hazard to man. The challenge is to find ever safer and more specific chemicals that have little or no effect on non-target organisms.


POISONS

The use of poisons to kill `problem animals' such as jackal, caracal, cheetah and leopard is causing serious declines in scavenging animals. Farmers often bait a carcass with a poison such as strychnine, and leave it in the veld in the hope that a jackal or caracal (the target species) will eat the meat and die. However, scavenging birds such as vultures, bateleurs and tawny eagles, all of which are very good at finding carrion, come down to baited carcasses and are poisoned. As the farmer never intended this to happen, these animals are called non-target species.

A number of scavenging raptors, e.g. Cape and Egyptian vultures, and bateleur eagles, have been driven to extinction over large areas as a result of this practise. Other species have declined to critically low numbers, e.g. lappetfaced and whiteheaded vultures, tawny eagles. Also severely affected have been non- target mammals such as the aardwolf, aardvark, bat-eared and Cape fox, brown hyaena and many smaller animals.


CONSERVATION ACTION

* In parts of Europe where the use of poisons is banned for predator control, bird of prey numbers have recovered well. It is high time that a similar ban is introduced in all countries in southern Africa. Although not banned, strychnine, one of the most common, and most lethal poisons used to bait carcasses, has to be prescribed by a veterinarian in order for a farmer to obtain it.

* The Redbilled Quelea Working Group has been formed to address the issue of controlling quelea (a gregarious, seed-eating bird that can cause tremendous crop losses). The application of Queletox (active ingredient fenthion, an organophosphate) to kill quelea, has resulted in widespread deaths of non-target species such as birds of prey and herons.

* Arsenic is no longer used in stock dips.


DID YOU KNOW?

* It is estimated that for every target animal poisoned, 100 - 300 non-target animals die.

* Although insectivorous, the aardwolf, aardvark, bat-eared fox, and Cape fox are vulnerable to poisoned carcasses as they are attracted to carrion for the maggots they will find there.

* At levels too low to cause death, organochlorines can disrupt the breeding of birds by causing shell-thinning, egg-breakage, and death of embryos in unbroken eggs. This results in population decline and local extinction.

* The yellowbilled oxpecker, formerly widespread in South Africa, had died out by 1910, mainly as a result of the introduction of arsenical dipping for livestock in 1902.

* Oxpeckers die within 48 hours after eating arsenic coated ticks.


FURTHER READING

VULTURES AND FARMERS. Vulture Study Group, Johannesburg, 1985.

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.

SCAVENGING RAPTORS ON FARMLANDS: WHAT IS THEIR FUTURE? C Brown. African Wildlife 42(2): 103-105. 1988.

"SUPERJAKKALS" AND THE POISON PEOPLE. J. Ledger. African Wildlife 40(3): 85-89. 1986.

CARELESS HANDLING OF PESTICIDES STILL CAUSES POISONING INCIDENTS. J. Ledger. African Wildlife 40(3): 91, 1986.

POISONING BY CHEMICALS IN AGRICULTURE AND PUBLIC HEALTH: TRADE NAMES, CHEMISTRY, CLASSIFICATION, TOXICOLOGY, SYMPTOMOLOGY AND TREATMENT PROCEDURES. H. Fourie. ENG Enterprises, Pretoria, 1984.


USEFUL CONTACTS

Endangered Wildlife Trust. Private Bag X11, Parkview 2122. Tel. 011-4861102.

Poison Working Group. PO Box 15121, Lynne East, 0039. Tel. 012-808 0592.

Vulture Study Group. PO Box 72334, Parkview, 2122. Tel. 011-646 8617.

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.

Provincial conservation authorities. See telephone book for details.

Poison Information Centre. For advise on cases of human poisoning: Johannesburg 011-642 2417, Bloemfontein 051-475 353, Cape Town 021-689 5227.


Created and maintained by: Jocelyn Collins
Last Updated: Thursday, February 01, 2001