Do mosquito control treatments of wetlands affect red-winged blackbird (Agelaius phoeniceus) growth, reproduction, or behavior?

We found no convincing evidence that reproduction, growth, or foraging behavior of red-winged blackbirds (Agelaius phoeniceus) were negatively impacted by treatments of wetlands with either Bacillus thuringiensis israelensis (Bti, applied as Vectobac-G granules) or methoprene (applied as Altosid sand granules). Most red-winged blackbird parameters examined varied annually and some differences were found before treatments began. In all cases, differences found before treatments were either found again during the treatment years or no patterns existed to suggest impacts of mosquito control treatments. Only 1 of the 22 variables examined indicated a significant difference between a treatment group and the controls; males in Bti-treated sites were larger than males in control sites during the treatment years. Clutch size indicated a significant treatment-by-year interaction and was higher in control areas as compared with Bti-treated areas in 3 of the 6 years of study; 2 years occurred before any treatments were applied. Data from benthic aquatic insect studies showed that aquatic insects were depressed in wetlands treated with both methoprene and Bti in July and August. However, it is unlikely that food available to avian species in these wetlands was lower during the breeding season (May and June). Other portions of the avian life cycle that may be affected include the dispersal of young birds within or to these sites and individuals that use wetlands during migration. Impacts on these aspects of the avian community and landscape- level effects of treatments were not addressed.