| I investigated the effects of spraying deltamethrin for tsetse fly control on bird populations in the Okavango Delta, Botswana. Because deltamethrin has low toxicity to vertebrates, effects on birds would have been indirect and caused by reductions in insect food supplies, not by poisoning. The northern half of the Delta was sprayed in 2001 and the southern half in 2002. I monitored resident bird populations at four sites (two in each spray block), using point counts to monitor forest birds, and transects to monitor acacia thornveld birds and water dependent birds. Birds were classified by diet as insectivorous or non-insect-dependent in order to check for declines in insectivorous birds which did not occur in non-insect-dependent birds. Sections of the 2002 spray block burned just as the spraying started. In the 2001 spray block, there were no declines of insectivorous birds, and varied results for non-insect-dependent birds. In the 2002 spray block, the Chitabe site showed declines in insectivorous forest birds, which were not strongly correlated with the spraying, and Nxaraxa showed no such declines. Greybacked bleating warblers (Cameroptera brachyura) decline at Chitabe, but not at Nxaraxa or either of the 2001 spray block sites. There was not a decline in the number of water dependent or acacia thornveld species detected before and after the spraying. While immediate large-scale population declines in insectivorous birds were not detected, small-scale and long-term declines could not be ruled out. Effects on behavior, diet, and reproductive success were not assessed. |
