Chapter 9: Occurrence of Small Mammals: Deer Mice and the Challenge of Trapping Across Large Spatial Extents

Small mammal communities living in sagebrush (Artemisia spp.) may be sensitive to habitat isolation and invasion by exotic grass species. Yet there have been no spatially explicit models to improve our understanding of landscape-scale factors determining small mammal occurrence or abundance. We live-trapped small mam- mals at 186 locations in the Wyoming Basin Ecoregional Assessment area to develop species distribution (habitat) models for each species. Most small mammal species (n = 14) were trapped at a only few loca- tions. As a result, we developed a small mammal model only for the deer mouse (Peromyscus maniculatus). Deer mice were associated with areas having moderately productive habitat as measured by Normal- ized Difference Vegetation Index (NDVI), increased grassland land cover, contagion of sagebrush land cover, and proximity to intermittent water. The proportion of big sagebrush (Artemisia tridentata) within 0.27 km, proportion of mixed shrubland within 5 km, soil clay content, and proximity to pipe- lines were inversely related to the occur- rence of deer mice. Understanding habitat characteristics for deer mice helps our over- all understanding of the ecological process- es within sagebrush habitats because deer mice act as predator, prey, competitor, and disease reservoir. Development of the em- pirical data necessary for spatially explicit habitat modeling of small mammal distri- butions at large spatial extents requires an extensive trapping effort in order to obtain enough observations to construct models, calculate robust detectability estimates, and overcome issues such as trap shyness and population cycling.