Northern saw-whet owl (Aegolius acadicus brooksi) COSEWIC update and status report: chapter 3

Species Information

Name and classification

The Northern Saw-whet Owl (Aegolius acadicus) belongs to the family Strigidae, the ‘typical owls’. There are four species in the genus Aegolius; two of these are found only in neotropical forests, while the Boreal Owl (Aegolius funereus) is found in boreal forests throughout the Holarctic. There are two subspecies of Aegolius acadicus; the nominate subspecies found in continental North America and closely adjacent islands and the focal brooksi subspecies found only on Haida Gwaii/Queen Charlotte Islands (Cannings 1998). Common names for this endemic subspecies include: Queen Charlotte Owl (Bent 1961, Johnsgard 1988), Haida Gwaii Saw-whet Owl and Queen Charlotte Saw-whet Owl. The French name for Northern Saw-whet Owl is Petite Nyctale.

Figure 1. Left: The brooksi subspecies of Northern Saw-whet Owl. (Photo by Jared Hobbs – used with permission). Right: adult Northern Saw-whet Owl specimens, acadicus subspecies on left, and brooksi subspecies on right. (Photo by Laurie Savard – used with permission. Specimens from Royal BC Museum).

Figure 1. Left: The brooksi subspecies of Northern Saw-whet Owl.(Photo by Jared Hobbs – used with permission). Right: adult Northern Saw-whet Owl specimens, acadicus subspecies on left, and brooksi subspecies on right. (Photo by Laurie Savard – used with permission. Specimens from Royal BC Museum).

Morphological description

The Northern Saw-whet Owl brooksi subspecies is a small owl about 20 cm in length (Figure 1). Reverse sexual dimorphism is strong; females are up to 20% larger than males. These owls have a relatively large head with a prominent round facial disk and no ear tufts. Their eyes are yellow to orange. Upper parts are a buffy brown colour, with buffy and white streaking on the crown that converges in a V-like pattern between the eyes. White ‘eyebrows’ are prominent in some individuals. Underparts are buffy and broadly striped with dark reddish-brown. The rounded wings are also buffy reddish brown colour, with lighter spotting on the scapulars.

Overall the brooksi subspecies has a darker plumage than the nominate subspecies (Figure 1), which characteristically has more white where A. a. brooksi has a buffy appearance, particularly on the underparts (Fleming 1916, Bent 1961, Guiguet 1978, Johnsgard 1988, Cannings 1993, Sealy 1998, Koenig et al. 1999).

Genetic description

Haida Gwaii hosts a diverse suite of endemic species and subspecies. Whether or not this radiation of new taxa is a result of Haida Gwaii being a glacial refugium has been of great debate (e.g. Scudder and Gessler 1989). More recent evidence suggests a glacial refugium on the continental shelf that is now below Hecate Strait (e.g. Byun et al.1997). In the case of the Northern Saw-whet Owl, genetic analysis of highly conserved regions of DNA (cytochrome b gene on mitochondrial DNA) revealed very little genetic differentiation between the subspecies, suggesting that the Haida Gwaii Saw-whet Owls diverged from a population of owls that migrated post-glacially from the mainland, likely from refugia to the south of the Cordilleran ice sheet (Byun 1998). To better reflect the shorter-term changes in the genetic structure of the Saw-whet Owls, comparative microsatellite DNA analysis between the two subspecies is ongoing (Kevin Winker, pers. comm.). 

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