Habitat Selection by an Insectivorous Rodent: Patterns and Mechanisms across Multiple Scales

Abstract

Patterns of habitat selection by small mammals reflect variation in availability of resources at a range of spatial and temporal scales. I investigated use of habitat by northern grasshopper mice ( Onychomys leucogaster ) in shortgrass prairie and related the patterns to distribution of vegetation and substrate and availability of arthropod prey. I used powder tracking to document use of microhabitats and live-trapping to estimate abundance on sites with different soil types and amounts of shrub cover (macrohabitats). At all spatial scales examined, mice used disturbances of soil (primarily pocket gopher mounds) and burrows more than expected based on abundance of these microhabitats, but showed no affinity for large shrubs. Furthermore, movement patterns suggested that mice concentrated activities in areas with high densities of mounds and burrows. Insect prey were more numerous on mounds than in other microhabitats and were generally more abundant in trapping areas where grasshopper mice were captured, especially in spring and early summer. Mounds and burrows provide arthropods with access to subterranean refuges, and the concentration and accessibility of prey, thus, may explain the intensive use of these microhabitats by mice. Microhabitat variables associated with mounds and burrows were better predictors of population density than was macrohabitat, which may reflect the spatial distribution and temporal predictability of insect prey. Although local abundance of grasshopper mice was best explained by availability of suitable foraging microhabitat, the relationship between these microhabitats and edaphic characteristics suggests that it may be difficult to separate the roles of microhabitat and macrohabitat for this wide-ranging species.