Occupancy Dynamics, Roost Habitat and Prey of Mexican Spotted Owls in Utah

Scientific Disciplines
Biological Sciences - Terrestrial
Montana State University
spotted owl
Zion National Park
prey selection
Strix occidentalis
spotted owls
roost habitat
effects recreation
canyon environments
occupancy dynamics
mexican spotted owls
Volume 18, No. 1-4

Occupancy dynamics, roost habitat and prey of 
Mexican spotted owls in utah
D.Willey, C. Hockenbary, J. Rotella, Ecology, Montana State University, Bozeman, MT 59717
Mexican spotted owls (Strix occidentalis lucida) occupy canyon habitats that have 
received less attention than owls in forested environments, and yet canyon environments 
represent a significant portion of the owl’s range. In Utah, the owls occupy narrow and steep-
walled canyons that attract high levels of human use, including climbing and hiking through 
nest areas, and human use levels have strongly increased in the canyons, for example, permits 
for access to popular climbs and hikes increased over 1700% during 1998 to 2002 in Zion 
National Park. To examine potential effects of recreation on the owls, we studied temporal 
variability of detection, occupancy, local extinction, and colonization probabilities. Our study 
sites included several National Parks and BLM resource areas. Our primary objective was to 
examine effects of recreation on site occupancy dynamics. We also investigated reproductive 
success, roost habitat, and prey selection. The analysis of detection rate showed strong support 
for constant detection probability of 89% for spotted owls among 47 sites. For both single 
owls and owl pairs we estimated initial occupancy rate of 83% for mesic sites and 43% for 
relatively xeric sites. We found that recreation was not associated with occupancy, detection, 
nor extinction and recolonization probabilities. Although reproductive rates varied by year, 
recreation was not negatively associated with production of fledgling owls per site. We also 
studied prey selection and roost habitat in the canyon environments. Roosts were placed on 
steep-walled cliffs with greater number of perches than adjacent habitats, and roosts possessed 
relatively high overhead tree cover, cool daytime temperatures, and thus a suitable thermal 
environment in the arid canyons. Pellets collected at roosts sites, upon dissection, indicated 
that rodents were primary prey, but also included birds, bats, and various anthropods. 
Woodrats (Neotoma sp.) dominated the prey frequency and biomass.