Laboratory and field evidence for the avoidance of California voles (Microtus californicus) by western harvest mice (Reithrodontomys megalotis)

The hypothesis that western harvest mice (Reithrodontomys megalotis) would avoid the scent of large, behaviorally dominant California voles (Microtus californicus) was investigated in both laboratory and field experiments. Reithrodontomys megalotis chose to build nests in boxes containing clean pine shavings rather than those bearing the odors of M. californicus when presented with a choice in the laboratory. Microtus californicus were indifferent to R. megalotis odors. Both species were strongly attracted to conspecific odors. When presented with pairs of clean live traps and traps bearing California vole scent in the field, R. megalotis were captured at significantly greater frequency in the clean traps. This response was strongest when harvest mice were in breeding condition. Results of this study support the hypothesis that interspecific avoidance of voles by harvest mice is a likely mechanism contributing to spatial separation between these species at high vole densities.