Three desert Artemisia tridentata communities in Rush Valley, Utah were trapped for small rodents during the summer of 1970 in a mark-recapture study. Population densities were estimated using several indices for each population category. Animals were weighed and rodent biomass calculated for each species throughout the summer. Populations, biomass, and other data were then analyzed to gain a better understanding of A. tridentata community types of the Great Basin. Peromyscus maniculatus, Eutamias minimus, and Reithrodontomys megalotis were common to area 1. Peromyscus maniculatus, E. minimus, and Perognathus parvus were common to areas 2 and 3. The peak estimated standing crops were 182.8, 143.1, and 129.7 g/acre for areas 2, 1, and 3 respectively. The population and biomass of area 2 peaked in mid-summer, area 1 in early summer, and area 3 in late summer. Results from a similar study indicate mountain A. tridentata communities may be less productive, in terms of rodent biomass, than desert A. tridentata communities at lower elevations.

The diurnal behavior and nocturnal roosting patterns of 28 bald eagles outfitted with tail-mounted radios were investigated in Rush Valley, Utah between January and March 1982-1984. Casting analysis and feeding observations indicated the principal food source was jackrabbit carrion. Jackrabbit availability declined from 1982 to 1984 and eagles responded by; 1) roosting closer to feeding sites, 2) shifting from canyon to valley roosts, 3) arriving later at and departing earlier from roosts, 4) decreasing diurnal activity, and 5) decreasing residence time. Foraging efficiency appeared to be maximized by experienced eagles using familiar feeding areas and by naive birds monitoring their activity. There appeared to be a slight (8.6%) energetic advantage to roosting at valley sites because of their proximity to feeding areas. This saving was presumably dissipated under adverse weather conditions when eagles selected the sheltered microclimate of canyon slopes. Twelve eagles were tracked during spring migration and all followed northward routes.