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

Food supply, breeding success and DDT residue accumulation were investigated as possible causes for the decline of White-headed Black Chat populations in woodland sprayed for tsetse fly control. Gut contents from 21 birds were examined. A variety of invertebrates had been eaten, but ants, especiallyCamponotus spp. (Formicidae: Formicinae),Pheidole spp. (Myrmicinae), and termites, especiallyOdontotermes spp. (Isoptera: Termitidae), predominated in the dry season. In the early rains, more beetles (Coleoptera (predominantly Curculionidae)) and fewer termites were eaten. Ant and termite activity at sprayed sites in the study area was as great as or greater than that at unsprayed sites. Ants (Camponotus spp.) from sprayed sites held mean residue levels of 8.71 µg g(-1) dry weight (max. 218 µg g(-1) dry weight) total DDT, of which 67% was unaltered DDT. Termites and beetles had mean residue levels of 3.32 µg g(-1) dry weight (max. 14 µg g(-1) dry weight) and 0.92 µg g(-1) dry weight (max. 8 µg g(-1) dry weight) total DDT, of which 44% and 37% was unaltered DDT, respectively. Fledging success of White-headed Black Chats in adjacent sprayed and unsprayed areas was similar. Residues of DDT, DDD and DDE were found in all 23 chat carcasses examined. Birds collected in the dry season (July) from an area sprayed one month before contained up to 2206 µg DDT, 367 µg DDD and 578 µg DDE, g(-1) extractable lipid (86, 17 and 27 µg g(-1) dry weight, respectively). On average, residue levels were 50 times higher than in birds from the unsprayed area, and 4 times higher than in birds taken from another, recently sprayed area in the early rains (November). It is concluded that DDT spraying did not reduce availability of prey or fledging success. Initial population decline in sprayed areas was due to a lethal accumulation of DDT residues from prey, especiallyCamponotus spp. ants. Possible reasons for continued decline for 2-3 years after spraying, are discussed.