EFFECTS OF GRASSHOPPER CONTROL PROGRAMS ON RANGELAND BREEDING BIRD POPULATIONS

We investigated the effects of grasshopper control methods on breeding bird populations in western rangelands. We estimated bird densities o n 13 treated and 11 untreated sites before and after grasshopper contr ol operations. Four different treatments were used in these applicatio ns: malathion, sevin-4-oil, carbaryl bait and Nosema locustae bait. Th ere were few differences among the 4 treatments in their effects on bi rd community parameters (total bird density, and species richness, div ersity, or evenness). Bird community parameters did not differ between spray and bait applications but sample sizes were small for bait trea tments. When data from ail treatments were combined for analysis, ther e was no difference in any of the bird community parameters between pr e- and post-treatment samples. Densities of western meadowlarks (Sturn ella neglecta), however, were significantly lower on treated than untr eated sites 10 and 21 days after treatment. We found no relationship b etween changes in bird numbers 21 days post-treatment and either the s ize of the area treated or the date of treatment (i.e., early or late in nesting season). Malathion is an acetylcholinesterase (AChE) inhibi tor, but brain AChE levels in birds collected on sites treated with ma lathion showed no significant inhibition. These results suggest that g rasshopper integrated pest management treatments generally have little effect on breeding bird communities but some insectivorous bird speci es may decline on rangeland treated with broad-spectrum insecticides b ecause of reduction in food base. Pesticide applications that have adv erse impacts on birds and other nontarget wildlife that prey on grassh oppers may be counterproductive to longterm integrated pest management goals.