Ecologists suspect that owls select specific areas based on prey availability. My objective was to determine and compare distributions and abundances of Mexican spotted owl prey species' within different vegetation types in the canyons and mesas of the Manti-LaSal National Forest in Utah. I conducted live-trapping during summer and fall, 1994-95. Woodrat species (Neotoma spp.) are the Mexican spotted owls primary prey species as determined by percent biomass. Peromyscus spp. are also important in terms of frequency. Woodrats were only captured in the canyons and were primarily captured within the pinyon (Pinus spp.) - juniper (Juniperus spp.) vegetation type. The Mexican spotted owls in southeastern Utah spend >75% of their time within the canyons and forage within pinyon-juniper stands in the canyons. Maintaining the present state of pinyon-juniper stands within the canyons may benefit Mexican spotted owl populations in the Manti-LaSal National Forest.

I used enclosures with exits for emigration to test whether house mice could regulate their numbers by emigration to two levels of resources. Exits had a water obstacle likley to be crossed only by true emigrants. Enclosures had excess food and water and the number of shelters was held constant. I introduced a pair of mice into enclosures about every other night, until no more would become residents. I ran 7 trials in single enclosures and 8 in double enclosures (2 single enclosures joined with a tunnel). The number of mice that stayed within a given size enclosure was consistant, and was 2.3 times higher in double enclosures than in single enclosures. Weather, predation, starvation, and disease did not act in any trials. My data support the contention that house mice can control their population numbers through spacing and emigration.

Encroachment of woody plants has occurred in many of the world's grasslands within the past 3 centuries. Mechanisms underlying these physiognomic shifts have not been adequately described. My objectives were to elucidate the roles of interference, herbivory, acorn maturation date and timing of precipitation on emergence and survival of Emory oak (Quercus emoryi Torr.) at lower treeline; and to evaluate how different frequencies of monitoring influence the results of demographic studies with woody plants. Seedling emergence was negatively affected by delays in precipitation and decreased soil moisture content. Seedling survival was negatively affected by overstory and understory interference and vertebrate herbivory. Most seedling mortality was attributed to desiccation. Woody plants should be monitored at least monthly to evaluate emergence and survival after one year. These results indicate that abiotic constraints are the primary factors structuring southwestern oak woodlands and savannas.

I monitored and recorded human activities in bighorn sheep habitat to determine the role of human activity in the decline of an indigenous population of bighorn sheep in the Pusch Ridge Wilderness, Santa Catalina Mountains, Arizona. I recorded hiker activity, sound levels, presence of dogs, and hunting activity in off-trail areas of bighorn sheep habitat from June 1995 to June 1996. Eighteen percent of hiker-groups entering the study area hiked off-trails in bighorn sheep habitat, and 8% were accompanied by dogs. Although I observed very little hunting activity in the area, noise disturbance may be a factor in the decline of the population. The cumulative affect of these and other activities probably contributed to the decline of the herd.

I examined the efficacy of a mitigation project in Avra Valley, Arizona that was established to provide wildlife access across the barrier created by the Central Arizona Project aqueduct. I monitored movements of 17 radiocollared desert mule deer (Odocoileus hemionus crooki) to determine if deer were using the corridor for access across the aqueduct and the 26 km wide valley. I also examined deer use of vegetation associations and proximity to landscape features. Four deer crossed the canal but stayed within 500 m of the crossing site. One deer traversed the valley via the corridor. Overall, 22.4% of deer locations were in the corridor land system. Female mule deer generally used the mesquite (Prosopis velutina)-burroweed (Isocoma tenuisecta) vegetation association more than it was available and the palo verde (Cercidium spp.)-mixed cacti association less than it was available. Female deer were generally closer to the CAP, housing developments, roads, and permanent water than random points.

I surveyed parts of Tucson, Arizona to determine numbers of burrowing owl (Speotyto cunicularia) burrows present, identify characteristics associated with burrow sites, and assess reproductive success. I measured habitat characteristics at 48 winter, 58 breeding, and 48 random burrows. Random burrows were closer to perches (P) and farther from wash banks (P) than were active burrows, and had smaller entrance dimensions (P). Winter burrows were farther from human activity than were breeding burrows (P). Active sites had less total vegetation, and less visual obscurity than did random sites. Owls may have selected open sites to facilitate detection of predators or prey. Urbanization sometimes created conditions which appeared to attract owls, but also destroyed burrows. An average of 2.31 young fledged from 116 active burrows during 1997-1998. While comparable to other studies of burrowing owls occupying urban environments, this was lower than rates typically reported for the species.

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