Effects of Grasshopper Control Programs on Rangeland Breeding Bird Populations

Abstract

We investigated the effects of grasshopper control methods on breeding bird populations in western rangelands. We estimated bird densities on 13 treated and 11 untreated sites before and after grasshopper control operations. Four different treatments were used in these applications: malathion, sevin-4-oil, carbaryl bait and Nosema locustae bait. There were few differences among the 4 treatments in their effects on bird community parameters (total bird density, and species richness, diversity, or evenness). Bird community parameters did not differ between spray and bait applications but sample sizes were small for bait treatments. When data from all treatments were combined for analysis, there was no difference in any of the bird community parameters between pre- and post-treatment samples. Densities of western meadowlarks (Sturnella neglecta), however, were significantly lower on treated than untreated sites 10 and 21 days after treatment. We found no relationship between changes in bird numbers 21 days post-treatment and either the size of the area treated or the date of treatment (i.e., early or late in nesting season). Malathion is an acetylcholinesterase (AChE) inhibitor, but brain AChE levels in birds collected on sites treated with malathion showed no significant inhibition. These results suggest that grasshopper integrated pest management treatments generally have little effect on breeding bird communities but some insectivorous bird species may decline on rangeland treated with broad-spectrum insecticides because of reduction in food base. Pesticide applications that have adverse impacts on birds and other nontarget wildlife that prey on grasshoppers may be counterproductive to long-term integrated pest management goals.