Northern saw-whet owl (Aegolius acadicus brooksi) COSEWIC update and status report: chapter 8

Limiting Factors and Threats

Population

Current evidence suggests that the population density and abundance of Haida Gwaii Saw-whet Owls is low (CIH, unpubl. data). This subspecies is endemic, non-migratory, and the population range is limited to the Queen Charlotte Islands archipelago. Thus, if too great a population decline occurs, there are no ‘source’ populations to draw on that would compensate for such a decline (Harrison 1993).

Habitat loss

The breeding habitat of Saw-whet Owls appears to be associated with mature and old forest. Although the specific parameters of mature and old forest that the owls use are not well understood, it is likely that nesting opportunities are greatest in this forest type (Doyle, unpubl. data). As the Saw-whet Owls rely not only on snags, but also on primary cavity nesters to create suitable nest cavities, habitat loss for a suite of species will therefore also affect this owl population. Further, young stands of regenerating forest likely lack the features important to foraging during the breeding season (Cannings 1993, Fraser et al. 1993).

Introduction of exotic species

Haida Gwaii has experienced introductions of numerous species, some of which may directly threaten Saw-whet Owls. Raccoons and Red Squirrels (see Interspecific Interactions) are both effective nest predators, and European Starlings may harass owls and cause nest abandonment. 

The introduction of Sitka Black-tailed Deer has decreased the diversity (species richness, turnover and total number of species) of understory vegetation in interior forest ecosystems (RGIS-FRBC 2001). This in turn is likely affecting the food availability of rodents, which appear to be an important prey item for Saw-whet Owls during the breeding season (Cannings 1993). As well, the owls may also be relying on various forest invertebrates for food during the breeding season, which are also known to decline with the high levels of deer browsing on Haida Gwaii (RGIS-FRBC 2001). 

Road-kill

As many Haida Gwaii Saw-whet Owls apparently move to coastal areas for feeding during the fall and winter, owls are hit by vehicles at that time of year between Skidegate and Tlell, where the highway closely follows the coastline (Sealy 1999, S. Sealy pers. comm.).

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