TEMPORAL AND SPATIAL PATTERNS OF SMALL MAMMAL DENSITY AND SPECIES COMPOSITION ON A RADIOACTIVE-WASTE DISPOSAL AREA - THE ROLE OF EDGE HABITAT

Small mammal populations inhabiting radioactive waste disposal areas c ould be important vectors of contaminant redistribution, given suffici ently high numbers. Earlier studies conducted at the Subsurface Dispos al Area (SDA) in southeastern Idaho found small mammal densities equal ing or exceeding densities in native habitat. Our live-trapping study was conducted in 1988 and 1989 to assess the role of edge habitat (whe re SDA crested wheatgrass [Agropyron cristatum] plantings and native s agebrush habitat are separated by an earthen dike) in facilitating use of this highly modified site by small mammals. Small mammals had a si gnificantly greater density in SDA edge habitat than in the interior. Total density of small mammals on and immediately around the SDA appea red to be less variable over time than density in native sagebrush hab itat for years when data were available. This phenomenon was largely a ttributable to steady or increasing SDA population densities of the mo st common species, Peromyscus maniculatus and Perognathus parous, duri ng 1988-89, when most small mammal species had below-average densities in surrounding areas. The variety of foraging options in edge habitat may have allowed these relatively opportunistic species to avoid wide spread population declines associated with drought years in 1988-89. M ovements by P. maniculatus across the boundary were common, suggesting that this species did indeed utilize both habitat types. Preferences for edge habitat could potentially be used to formulate strategies tha t reduce use of the waste site by small mammals.