Fire severity and pre-fire forest composition affect Northern Hawk Owl presence in burned forests in western North America

Wildfire is an important natural disturbance shaping the boreal forests of North America. Not surprisingly, many species have adapted to benefit from the structural or functional changes in response to fire. Of these post-fire species, the Northern Hawk Owl (Surnia ulula caparoch) is one of the least studied species on the continent. We surveyed 18 recent fires in the boreal forest region of Alberta, Canada, ranging in age from 1 to 14 years post -fire, to improve our understanding of post-fire habitat relationships for this species. Hawk owls were present in fires ranging from 2 to 11 years post-fire, and occupied burns ranging in size from 1,000-272,000 ha. Hawk owls were strongly associated with areas of older deciduous-dominated forest, based on pre-fire forest inventory. Hawk owl responses to pre-fire forest age structure and composition were consistently stronger at the 1000 m radius (home range) extent than the 400 m (nest site) extent. We also found hawk owls responded differently to time since fire, with an immediate (e.g. 2-6 yr) response to low severity fire and a delayed (10-11 yr) response to high severity fire. We recommend future surveys for this species be conducted earlier in the day, ideally within a few hours of sunrise, based on the timing of detection in this study. Finally, the retention of large patches (e.g. > 300 ha) of older, deciduous-dominated habitat within post-fire forests may be an important management consideration for the conservation of hawk owls and other post-fire species.

Automated summary

Wildfire is a significant factor in shaping the boreal forests of North America, and the Northern Hawk Owl is one of the least studied species in relation to it. Through a survey of 18 recent fires in Alberta, Canada, it was found that the owl is strongly associated with older deciduous-dominated forest areas. The owl responded differently based on the time since the fire, showing an immediate response to low severity fires and a delayed response to high severity fires.