Habitat use by flammulated owls in northeastern Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5t34sp75v

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  • The reproductive ecology, diet and habitat used by flammulated owls (Otus flammeolus) during the breeding seasons of 1983 and 1984 were studied in northeastern Oregon. Remote photography was used at 5 nest cavities to record diet; radiotelemetry was used to determine habitat used for home ranges, nesting, roosting and foraging by 5 male owls; arthropod window traps were used to sample relative abundances of prey between 3 habitats. Density of breeding pairs was estimated at 0.47/40 ha. Home range areas averaged 10.3 ha. The diet (N=352), monitored after hatching, spanned 8 orders of arthropods but 62% of the prey items and 85% of the biomass were order Orthoptera. Relative proportions of arthropods trapped were greatest in grassland habitat (70% of total) and least in mixed conifer habitat (8% of total). Of 5 owls monitored while foraging (N=352 locations), 4 used ponderosa pine (Pinus ponderosa)/Douglas-fir (Pseudotsuga menziesii) forest type and 5 used the edge between forests and grasslands significantly more than these types occurred within their home ranges. Owls used roost stands (N=37) of mixed conifer forest type significantly more than it occurred on the combined home ranges, however, within roost stands, flammulated owls selected ponderosa pine trees for roosts over grand fir (Abies grandis), western larch (Larix occidentalis) or Douglas-fir. This may be related to predator avoidance since flammulated owls are better camouflaged in ponderosa pine than in the other tree species. Nest sites were selected apparently for the surrounding forest stand and ground cover rather than for any variable measured at nest cavities or trees. Owls used forest stands characterized by ponderosa pine/Douglas-fir species composition, trees 30-50 cm dbh, canopies with less than 50% closure and slopes of 16 to 25 percent significantly more than these occurred on the study area. Characteristics of ground cover at nest sites included dominance by several species rather than by a single species, combination of types (grass, forb, shrub) and greater than 33% ground coverage. These forest stand and ground cover characteristics are interrelated and likely influence prey populations. Timber production may affect habitat used by flammulated owls for breeding. With suitable management, however, timber production and viable populations of flammulated owls may be compatible.
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