Trap Elevation and Biotic Factors Influence Capture Frequencies of Western Harvest Mice (Rei

Abstract

Western harvest mice, Reithrodontomys megalotis, are used as a prairie indicator species but low capture probabilities in Indiana may make them unreliable for this purpose at this eastern edge of their range. To increase capture probabilities, researchers have experimented with vertical trap elevation with varying degrees of success. Our objective was to investigate if elevated traps increased captures of R. megalotis and to determine if competition for traps with meadow voles, Microtus pennsylvanicus, contributes to this pattern. To investigate these questions a 536 grid of trapping stations with 15 meter spacing was established in the Purdue Wildlife Area. Three Sherman traps; ground, semi-elevated, and elevated, were placed at each station. Independence of frequency of capture in the vertical strata was compared between these two species using a G-test. We rejected the null hypothesis of independence between trap vertical strata and small mammal species, providing support for the role of competition for traps as contributing to differences in captures of R. megalotis across the vertical stratum. Post hoc tests were then conducted to determine significance in trap comparisons. Significance was found in ground vs. elevated and semi-elevated vs. elevated traps. Surprisingly, 24 captures of M. pennsylvanicus were recorded in the higher stratum traps, despite no previous records of captures of this species above the ground. These results suggest when using R. megalotis as an indicator species of prairie health in Indiana, investigators should elevate traps.