Distribution and breeding ecology of boreal and northern saw-whet owls in the Boreal forests of Alberta, Canada

  • Author / Creator
    Domahidi, Zoltan
  • The boreal forest is an ecologically dynamic region with a long history of natural disturbances. These dynamics now run at a different and more rapid pace in Alberta because of land-use change, forestry, and developments in the energy industry. Although boreal owls Aegolius funereus and northern saw-whet owls Aegolius acadicus are considered forest associated species, little is known about their distribution and breeding ecology in the boreal region of Alberta. In this thesis, I address this gap by evaluating what influences the spatial distribution of these owls during the breeding period across Boreal Alberta, while also assessing their habitat use and breeding performance in forests affected by variable green tree retention harvesting in northwest Alberta. For the first objective, I used acoustic recordings from 667 autonomous recording units (ARU) to document the presence of the targeted species and modelled these locations with climate, biotic, landscape, and forest disturbance variables using boosted regression trees to explain spatial patterns in owl occurrence across the region. Second, I investigated owl habitat use and breeding performance during 2016 by placing and monitoring 169 nest boxes in forest patches characterized by a combination of available cover types and harvest retention levels. Average minimum winter temperature contributed most to explaining the final distribution of boreal owls, while the most important predictor of northern saw-whet owl distribution was amount of cropland at the home range scale (i.e., 564-m buffer around each ARU). Human disturbances affected distribution of these owl species differently. Northern saw-whet owls were most often found near openings created by linear disturbances at the nest site scale (i.e., 150-m buffers), while boreal owls were associated with landscapes containing low levels of linear disturbances at the home range scale. The nest box experiment provides the first Canadian assessment of the habitat use and breeding performance of boreal and northern saw-whet owls in partially harvested boreal forests. Boreal owls chose nest boxes placed in conifer-dominated stands with at least 50% green tree retention. In contrast, northern saw-whet owls were more tolerant of forest harvest, breeding in boxes placed in deciduous-dominated stands with at least 20% post-harvest tree retention. Results confirm that northern saw-whet owls bred in northwestern Alberta at >55 °N, a significant extension of known breeding range, but suggest that boreal owls have low productivity in these forests as shown in other areas that have been studied. This thesis highlights the advantages of combining passive audio surveys with distribution modelling, and the potential of local networks of nest boxes to obtain detailed information about two cryptic and under-studied species in the boreal forest.

  • Subjects / Keywords
  • Graduation date
    Spring 2018
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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