Responses of boreal forest owls to landscape patterns originating from fire and timber harvest.

摘要

This thesis investigated the effects of forest fire and industrial harvesting disturbance on forest dwelling owls. The underlying assumption of various forms of natural disturbance emulation is that harvest can be used to mimic wildfire as a disturbance agent, in spite of their differences. I tested the effects of disturbance type and history on local calling behaviour and occurrence probability of four sympatric species of forest-dwelling owls at a provincial scale. I found the amount and nature of disturbed area and disturbance history to be non-significant in predicting occurrences of Northern Saw-whet Owls, Boreal Owls, and Barred Owls. However, amount of recent harvest was negatively associated with Great Gray Owls, and age since fire disturbance was positively associated. These results suggest that, at a broad scale, harvest is a suitable mimic for the former three species, and less so for the latter. However, animals may respond differently to different habitat features at different scales. I tested for the effects of harvest versus fire disturbance on habitat use by Boreal Owls at a landscape scale. Habitat use models differed between fire and harvest-origin landscapes, and failed to successfully predict owl locations on alternate landscapes. These results suggest Boreal Owls behave differently on landscapes originating from differing disturbance events. More research is needed to define and measure the demographic consequences of this behaviour. Finally, I examined what structural features influence perch and nest-site selection by Northern Hawk Owls, a species that will likely benefit the most from the creation of large, harvest origin openings. I found that perch-sites were selected based on height, openness and amounts of surrounding small mammal habitat, and nest sites were selected based on prey availability. Thus, remnant snags and coarse woody debris are factors that promote Hawk Owl use, are under control of harvest management, and are therefore important considerations with respect to this species' establishment. Managers must decide whether promoting the establishment of these birds is conducive or detrimental to emulating nature using forest harvesting.