Common prey for the northern spotted owl consists of small mammals, particularly nocturnal arboreal, or semi-arboreal species and includes flying squirrels, lagomorphs, and deer mice (NatureServe 2002j). Northern spotted owls typically roost during the day and hunt at dusk and at night.
Nesting occurs on broken treetops, ledges of cliffs, natural tree cavities, stick platforms in a tree, caves, and often in abandoned hawk or mammal nests. Nest sites are located where the proportion of old growth and mature forest habitat is great. Pairs tend to occupy the same nesting territories in successive years if the habitat remains suitable (NatureServe 2002j). Northern spotted owl pair territories may range from as small as 530 km2 in old mixed conifer forest to 2,900 km2 in old Douglas-fir forest (Carey et al. 1992 in NatureServe 2002j). They may move nest sites frequently within the territory (Laye pers. comm. 2002). Breeding and egg laying occur in early April in Oregon and the typical clutch size is two. The female incubates the eggs for about 30 days, and during this time is fed by the male. Young owls leave the nest at about five weeks old and fledge at about six weeks old. They become independent from the adults by about October. Northern spotted owls first breed at two to three years of age and may not breed every year (NatureServe 2002j).
Northern spotted owl pairs and individuals have been negatively affected by activities resulting in habitat loss or fragmentation. These can include natural disturbances such as intense fires, but are most often caused by logging mature and old growth forest stands. Recently, the barred owl has expanded its range into the Pacific Northwest and could possibly compete with or displace the northern spotted owl (very rare occurrences of hybridization have also been detected) (Hamer et al. 1994 in NatureServe 2002j).
A conservation strategy has been described that defines habitat conservation areas containing a minimum of 20 pairs of northern spotted owls. Further, sound management practices should include efforts to control factors that adversely affect survival of adult females (NatureServe 2002j). Where old growth is lacking, silvicultural manipulation of vegetation and creative snag or den tree management could be used to accelerate the development of northern spotted owl habitat.
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