Effects of DDT treatments applied for tsetse fly control on White-headed Black Chat (Thamnolaea arnoti) populations in Zimbabwe. Part I: population changes.

Surveys of relative abundance were made in DDT-treated and untreated woodland in NW Zimbabwe using playback of tape recorded song. Chats were common in old stands of untreated mopane (Colophospermum mopane) and miombo (Brachystegia spp.) woodland but were less common in suitable habitat which had been sprayed with DDT at the rate of about 200 g ha(-1) for tsetse fly control. Population changes in the Siabuwa Communal Area were related to spraying operations over 3.5 years from July 1987 to January 1991. In the 1987-89 treatment area, numbers fell by 88% over 33 months following first treatment, mainly due to a reduction in occupied sites. Groups were smaller and single sex groups more frequent in treated areas compared with an adjacent unsprayed area. Numbers in the unsprayed area fell by 13% over the same period. Total numbers and number of groups at the edge and just within the treated area increased temporarily after each of the first two sprays. At the end of the study, numbers in the 1987 and 1987-89 treatment areas were increasing, and isolated groups were found in the 1984-89 treatment area. In a second study area, a further treatment of DDT, one year after the first, was followed by a 74% decline in numbers over nine months. It is concluded that tsetse spraying operations have had a severe, and possibly prolonged, impact on the White-headed Black Chat population of NW Zimbabwe.