ROOST HABITAT OF MEXICAN SPOTTED OWLS (STRIX OCCIDENTALS LUCIDA) IN THE CANYONLANDS OF UTAH

摘要

In large portions of their geographic range, Mexican Spotted Owls (Strix occidentalis lucida) roost in forest-dominated environments, but in some areas the owls use relatively arid rocky canyonlands. We measured habitat characteristics at 133 male roosts (n = 20 males) during 1992-95, and 56 female roosts (n = 13 females) during 1994-95 in canyon environments of southern Utah. Across all years, 44% of Mexican Spotted Owls' roosts were located in small stands of mixed-conifer forest, 30% in desert scrub vegetation, 16% in pinyon-juniper woodlands, and 10% of roosts were in riparian habitat. Roost sites were located in canyons composed of cliff-forming geologic formations. The width of canyons measured at roosts averaged 68.6 m (8.2 SE), and ranged from 1-500 m. The mean height of cliffs at roost sites was 77 m (10.9 SE) and ranged from 6-411 m. Roosts were located at caves and ledges (46% of all roosts) or in various tree species (54%). Roost height above ground averaged 9.5 m overall (1.1 SE), with mean tree roost height of 3.7 m (0.2 SE), and cliff roost height equal to 17.2 m (2.2 SE). For both males and females, coniferous trees species were used most frequently (64%), primarily Douglas-fir (Pseudotsuga menziesii), white fir (Abies concolor), and Utah juniper; and 36% of roosts occurred in deciduous trees, including big-tooth maple (Acer grandidentatum), boxelder (A. negundo), and Utah serviceberry (Amelanchier uthaensis). Canopy cover of tress at roosts ranged from 44-71%, mean tree height of trees present was 9.5 m and mean diameter of trees was 25.4 cm. Upland habitats that were not used for roosting were warmer, not as steep, possessed fewer caves and ledges, and trees present were of smaller stature than trees present in roost habitat.