As winter takes hold, top tier predators such as Great Horned Owls often switch hunting strategies in order to survive. They wander, often widely, in search of prey. This is especially true of owls breeding throughout the boreal forest. What this means for southern Ontario birders is that birds quite distinct from their local breeders, the reddish-brown B. v. virginianus, may be observed. In Ontario, using B. v. virginianus as a starting point, there is a V-shaped cline toward paler, grayer and overall “colder” tones to the NW (B. v. subarcticus in prairie provinces and extreme NW Ontario & B. v. “scalariventris” throughout northern Ontario) and darker, blacker, less rufescent and more “sooty” tones to the NE (B. v. heterocnemis in central Quebec, east to Newfoundland and Labrador). As ever, the boreal forest east of the Rockies presents limited geographic barriers, and as such, clines, vs. crisp geographic delineation between subspecies, are likely to be observed. What this means in terms of putting a designation on an intriguing migrant Great Horned Owl is that a subspecies name may best be cushioned with a prefix such as “suggestive of” or “probable.”
Photo: Great Horned Owls, from left to right: B. v. subarcticus, B. v. viginianus and B. v. heterocnemis. Canadian Museum of Nature collections.
An FYI for Ottawa birders: that remarkable, pale Great Horned Owl to the left in the photo below was collected at Shirleys Bay in January 1975 by the late Richard Poulin.