Home range and habitat of breeding flammulated owls in Colorado

-We used radiotelemetry to determine habitat use by Flammulated Owls (Otus flammeolus) during the breeding season on 452 ha of montane conifer forest in central Colorado in 1982-1983. Mean size and SD of home ranges was 11.1 ? 1.9 ha (range = 8.5-12.5 ha, n = 4) in 1982 and 18.3 ? 5.1 ha (range = 14.0-24.0 ha, n = 3) in 1983. Habitat use by nesting males was affected by distribution of old forests of ponderosa pine (Pinus ponderosa) mixed with Douglas-fir (Pseudotsuga menziesii), by topography, and by juxtaposition of home ranges of conspecifics. In spring, both new and returning owls settled into areas containing more old ponderosa pine/Douglas-fir than in other overstory types available in the study area. After settling, males foraged significantly more often in old ponderosa pine/Douglas-fir than in other overstory types available within home ranges. Eighty-one percent of foraging locations by males occurred in one to four intensive foraging areas within each home range. Mean size of intensive foraging areas was 0.5 + 0.4 ha (range = 0.1-1.4 ha). Eighty percent of intensive foraging areas consisted entirely of old ponderosa pine/Douglas-fir. Use of this overstory type by Flammulated Owls is probably related to its composition and structure, and prey availability. Received 24 Jan. 1997, accepted 19 April 1998. When settling into landscapes birds must distinguish among available habitats, each of which may differ in quantity and quality of requisite resources (Fretwell and Lucas 1970). Habitat selection during settling likely involves an hierarchically-ordered series of choices during which a bird selects a geographic area (first-order), types of habitat in which the territory is established (secondorder), and specific microhabitats for activities such as nesting, foraging, and roosting (thirdorder; Johnson 1980). At each order of selection a species may use different criteria for discriminating among available habitats. Western Kingbirds (Tyrannus verticalis), for example, may select territories on the basis of maximum canopy height, and nest-sites (microhabitats) on the basis of tree characteristics (Bergin 1992). Habitats selected at each order are limited by the preceding choice because movements of breeding birds are energetically limited to some finite area around nests. Descriptions of habitat are therefore scale-dependent (Wiens 1986, Kotliar and Wiens 1990) and focusing on a single order may preclude discerning patterns at other orders (Maurer 1985). Understanding a species' habitat selection requires the consideration of choices at each scale. The breeding range of Flammulated Owls (Otus flammeolus) is from the Rocky Mountains to the Pacific Coast Mountains (except Oregon and Washington) and from south-central British Columbia to Veracruz, Mexico (McCallum 1994). Flammulated Owls are migratory and may winter from the southern United States to as far south as El Salvador (Phillips et al. 1964, American Ornithologists' Union 1983). Habitats within home ranges of Flammulated Owls have not been compared to habitats available within landscapes. Nesting Flammulated Owls have been reported in yellow pine [subsect. Ponderosae (Critchfield and Little 1966)] and mixed-conifer forests. These forests were often mixed with oak (Quercus sp.) or pinyon (Pinus edulis) at lower elevations, and fir (Abies sp.), Douglas-fir (Pseudotsuga menziesii), or quaking aspen (Populus tremuloides) at higher elevations (e.g., Marshall 1957, Bull and Anderson 1978, Richmond et al. 1980, Goggans 1986, Reynolds and Linkhart 1987, McCallum and Gehlbach 1988). Nesting Flammulated Owls were occasionally found in pinyon (Huey 1932) and Douglas-fir forests (Howie and Ritcey 1987, Powers et al. 1996). We determined habitat selection by Flammulated Owls at multiple scales by comparing forests within owl home ranges to forests ' USDA Forest Service, Rocky Mountain Research Station, 240 West Prospect, Fort Collins, CO 80526. 2 Department of Fishery and Wildlife Biology, Colorado State University, Fort Collins, CO 80523. 1 Current Address: Dept. of Environmental, Population, and Organismic Biology, Univ. of Colorado, Boulder, CO 80309; E-mail: linkhart@colorado.edu. 4Corresponding author.