Reproduction and nest behaviour of Tennessee warblers Vermivora peregrina in forests treated with Lepidoptera-specific insecticides.
A study was carried out to test the hypothesis that food reductions caused by forest spraying with Lepidoptera-specific insecticides would affect Tennessee warbler behaviour and reproduction. Tennessee warbler nests and parental behaviour were monitored in two spray blocks, one treated with Bacillus thuringiensis (Bt) and the other with tebufenozide (MIMIC), and in an untreated control area. Nestling survival and growth were unaffected by the insecticide treatments. Nests in the treated blocks had smaller clutches, smaller broods and lower hatch rates than nests in the control block, but these differences were not statistically significant. Nestling diets were similar in the MIMIC and control blocks. There were slight differences in the behaviour patterns of female Tennessee warblers in the MIMIC and control blocks. MIMIC females spent less time at the nest and more time foraging. The results of this study suggest that the indirect effects of forest spraying with Lepidoptera-specific insecticides pose little risk to forest songbirds.