Activity and diet of bats in conventional versus organic apple orchards in southern Michigan

Abstract

Organic farming practices have been suggested as a conservation strategy that can provide productive foraging sites for insectivorous bats in agricultural areas. We tested the hypothesis that the number and diversity of insects captured and the resulting activity and diet of bats would differ between organic and conventional apple orchards. During the summer of 2009 and 2010, we captured 131 Big Brown Bats (Eptesicus fuscus) and five Eastern Red Bats (Lasiurus borealis) by mist netting in four organic and four conventional orchards in Michigan. Acoustic monitoring revealed that most calls (59%) were produced by Big Brown Bats, followed by Hoary Bats (L. cinereus), Eastern Red Bats, and unidentified species of Myotis. Most insects (96%) captured in light traps were Coleoptera, Diptera, Hemiptera, Lepidoptera, and Trichoptera; fecal analysis indicated that Coleoptera dominated the diet of Big Brown Bats (79% by volume), followed by Diptera (14%). There were no significant differences between organic and conventional orchards in number of insects captured with light traps, bats captured with mist nets, acoustic recordings of bats, or proportion of Coleoptera and Diptera consumed by the bats. However, the taxonomic composition of captured insects and acoustic recordings was not homogenous among orchards in either group, suggesting that factors other than farming practices were more important in determining which insects and bats were found in the small orchards typical of southern Michigan.