Graduate Thesis Or Dissertation
 

Habitat selection by Northern Pygmy-Owls on the Olympic Peninsula, WA

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  • Landscape level habitat alterations can have different effects on different species. Species that are more highly specialized for some important aspect of their natural history are expected to be more sensitive to habitat alteration than are those that are generalists. The Northern Pygmy-Owl (Glaucidium gnoma) has been suggested as a research and conservation priority due to the presumed negative effects of recent habitat alterations such as forest fragmentation and partial forest clearing. However, Pygmy-Owls are considered to be habitat and food generalists and may have an affinity for forest openings and edges. We tracked nine radio-marked male Northern Pygmy-Owls during the breeding seasons of 1996 and 1997 on the Olympic Peninsula, WA to examine three aspects of their natural history: cover type selection for foraging, nest location with respect to edges and dietary composition. Predictions of the generalist model were that use of resources would reflect availability. Cover types were divided into seven categories generally reflective of seral stage development. Individual owls were located an average of 3.7 times per week (45 times overall) and cover types used for foraging were compared to those available within home ranges. Pygmy-Owls used all of the available cover types for foraging but preferred structurally complex and mature cover types over structurally simple and young cover types. There was no evidence of preferential use of edges for foraging, but there was suggestive evidence that nests tended to be near edges. The diet was dominated by birds and mammals. Estimates of dietary composition varied depending on the method used. Pygmy-Owls appear to forage on those prey species that are most abundant or most easily captured. Our results suggest that Northern Pygmy-Owls may be relatively insensitive to habitat alterations affecting prey species assemblages and relatively more sensitive to habitat alterations affecting structural characteristics.
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