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Wildlife Conservation

Recovery of Wildlife in Zimbabwe following Ground-spraying with DDT
for Tsetse Fly Control - Zimbabwe 1998 - 1999

Clients: Department for International Development, UK and Tsetse Control Branch, Department of Veterinary Services, Zimbabwe
R.J. Douthwaite, Project Director

Initial investigation in the early 1980s confirmed that tsetse control operations were the main source of DDT in wildlife and it was recommended that a more detailed assessment should be undertaken. The subsequent study, from 1987 to 1991, examined the impact of residues in woodland on soil micro-organisms, invertebrates, lizards, birds and insectivorous bats. It also investigated effects on fish and invertebrates in seasonal streams and fish and fish-eating birds, including the Fish Eagle, in Lake Kariba.

Despite the relatively low application rate of DDT and rapid dissipation of residues under tropical conditions, clear evidence of actual or potentially deleterious effects of DDT was found in several wildlife species. In particular, populations of four woodland birds and a lizard were significantly reduced in sprayed areas although none was exterminated. No effects on fish were found and there was good evidence that DDT had little or no impact on a range of other terrestrial species and ecological processes.

It was predicted that effects of DDT were probably reversible within 10-20 years. The present project, carried out in 1998-1999, aimed to validate predicted recovery rates and extend the impact assessment nine years after DDT treatments ended.

Ant, lizard, bird and bat populations and current exposure levels were measured at earlier study sites and the changes assessed. Recovery was confirmed, and in all but one species population levels in sprayed and unsprayed areas were similar. Recovery in one species, the white-headed black chat, was incomplete but well advanced, and it was estimated that full recovery from exposure to 3 or more DDT treatments would take up to 15 years.

It was concluded that the use of DDT under controlled and limited-dose applications for tsetse fly eradication did not give rise to any irreversible damage in the wildlife populations or ecological processes investigated, and that full recovery may be expected within 15 years.

It was apparent that the impacts of DDT on wildlife populations were less than those arising from annual or seasonal changes in climate, or spatial variation in habitat.

Moreover the impact of DDT on biodiversity appeared trivial compared with the effects of large-scale woodland clearance by farmers in the Zimbabwe valley, or woodland destruction by unmanaged elephant populations within the protected area system (Douthwaite, R.J. 1999. DDT in the Tropics: Recovery of Wildlife in Zimbabwe following Ground-spraying for Tsetse Fly Control. Canterbury, UK; R J Douthwaite & Associates).


 

Page last updated October 2, 2013