RESPONSE OF BREEDING BIRDS TO MOSQUITO-CONTROL TREATMENTS OF WETLANDS

We examined the possible effects of mosquito control treatments of wet lands with Bacillus thuringiensis israelensis (Bti, applied as Vectoba c-G granules) and methoprene (applied as Altosid sand granules) on wet land breeding bird communities. Data collected two years before (1988 and 1990) were compared to data collected three years after (1991-1993 ) treatments were applied. Total numbers of species and individuals ob served remained relatively constant throughout the study period, but s everal individual species varied annually, most likely due to changes in water levels and habitat available. We found no effect of Bti or me thoprene treatments on the bird community or on 19 individual bird spe cies. The few differences that were observed between control and treat ment were inconsistent over time and were likely due to chance because of the large number of comparisons that were completed. Despite relat ively large reductions of aquatic insects (including mosquitoes) in mi d-to late-summer following both treatment types, it is unlikely that f ood available to bird species in these wetlands was depressed during t he breeding season. Effects of weather and predation were probably mor e important influences on species and community parameters than was mo squito control treatment during the study period. Because of lower aqu atic insect densities in mid- to late-summer, other parts of the avian life cycle such as late summer survival, dispersal of young birds, or migrating birds may be more affected by mosquito control treatments.