There are actually two subspecies of northern saw-whet owl – the common saw-whet that occurs throughout North America, Aegolius acadicus, and the subspecies Aegolius acadicus brooksi on Haida Gwaii, off the northwest coast of British Columbia. The Haida Gwaii population is endemic and does not migrate off of the archipelago (Cannings 1993, as cited in Cannings 2004), but there are a few cases of mainland saw-whets migrating to the islands (Sealy 1998, as cited in Cannings 2004). The plumage of the Haida Gwaii saw-whet is darker and more overall buffy coloured and has a more mottled breast than the continental counterpart. Their call is also slightly higher pitched (Cannings 2004).

The diet of the Haida Gwaii population is similar to the continental populations, but analysis of stomach and pellet contents, foraging observations and tissue isotope analysis have shown that this subspecies is more opportunistic than A. acadicus and feeds on a wide range of small animals. Their main source of protein during breeding seasonis also deer mice of the genus Peromyscus, as well as shrews of the genus Sorex, but they will also eat small birds, often passerines  (e.g. warblers and kinglets) and fledglings of shorebirds and alcids (e.g. ancient murrelets (Synthliboramphus antiquus); Cannings 2004). The major difference in diet between the two subspecies is that the Haida Gwaii saw-whets will take advantage of the abundance of intertidal invertebrates (mainly amphipods and isopods) as a major source of protein and have been seen foraging on sandy beaches among rotting kelp, primarily after breeding and in between breeding season (Hobson and Sealy 1991, as cited in Cannings 2004; Sealy 1999). Remnants of western toads (Bufo boreas) have also been found in the stomach contents of some specimens (Sealy 1999).

Like the mainland species, the Haida Gwaii saw-whet owl is also a secondary cavity nester, relying on naturally occuring tree cavities or holes (at least 7.5 cm in diameter opening) already made by woodpecker species. They have been observed using nest boxes as well. Only two nest sites have actually been described on Haida Gwaii (Cannings 2004). These saw-whets prefer old growth conifer forests near riparian zones with an open understory and abundant nesting holes and tree snags. They inhabit the Coastal Western Hemlock Biogeoclimatic Zone and nest mainly in Western Hemlock (Tsuga heterophylla) and Sitka Spruce (Picea sitchensis). Nests may be limited for northern saw-whets on Haida Gwaii, as there are no pileated woodpecker on the islands, which usually provide roosting sites for many mainland owls. They are known to use cavities made by the northern flicker (Colaptes auratus) and smaller woodpeckers like the red-breasted sapsucker (Sphyrapicus ruberand) and the hairy woodpecker (Picoides villosus) (Cannings 2004). However, the hairy woodpecker is also an endemic subspecies with a small population size, and evidence suggests that population dynamics of the saw-whet owl may be correlated with those of the hairy woodpecker in some areas of Haida Gwaii (COSEWIC 2006).

The estimated population of adult saw-whets on Haida Gwaii is about 1900, over an area 8500 km^2 of their main habitat (Cannings 2004; COSEWIC 2006). Many factors have been contributing to the slow decline in abundance of this subspecies on the islands. Due to increased logging and deforestation and destruction of their breeding and foraging habitat (see map below), as well as their small population size and endemic nature, the saw-whet owl population has been steadily decreasing at around 2-4% per year (Cannings 2004). The fact that the Haida Gwaii population is a subspecies means there is no possibility for a rescue effect to help increase the population. This is because the population does not migrate off the islands, and the mainland species does not contribute to the Haida Gwaii population, as they do not interbreed (COSEWIC 2006). The introduction of Sitka black-tailed deer (Odocoileus hemionus sitkensis) has led to alteration of understory vegetation, which could lead to changes in availability of important small mammal, bird and invertebrate prey for this species (COSEWIC 2006). This subspecies has few predators, due to the lack of nocturnal raptors on Haida Gwaii, and only Northern Goshawks (Accipiter gentilis) have been observed taking these owls. However, these saw-whets can be vulnerable to nest predators like the American Marten (Martes americana), and introduced species like the Red Squirrel (Tamiasciurus hudsonicus) (Martin & Joron 2003) and Common Raccoon (Procyon lotor) (Eder & Pattie 2001). This subspecies may also compete for nesting habitat with introduced European Starling (Sturnus vulgaris) (COSEWIC 2006).

Haida Gwaii saw-whet owls are on the provincial Blue List in British Columbia and were listed as threatened by COSEWIC (Committee on the Status of Endangered Wildlife in Canada) in 2006. These owls are also listed under Appendix II of the Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES; COSEWIC 2006). They are protected by the provincial Wildlife Act, and the presence of the Gwaii Haanas National Park Reserve, located on the southern tip of Haida Gwaii, and the Naikoon Provincial Park in the northeast, also serve to protect precious habitat required for successful breeding populations of the this subspecies (COSEWIC 2006). Riparian and old growth forest management and conservation is also a major factor in preventing the extinction of the Haida Gwaii saw-whet owl (Cannings 2004).

References

Cannings, R.J. 1993. Northern Saw-whet Owl (Aegolius acadicus). Pp. 20 in Poole, A.
and F. Gill (eds.). The Birds of North America. The American Ornithologists Union,
Washington, DC.

Cannings, R. J. 2004. “Queen Charlotte Northern Saw-whet Owl”. Accounts and Measures for Managing Identified Wildlife. 7 pp.

COSEWIC. 2006. COSEWIC assessment and status report on the Northern Saw-whet Owl brooksi subspecies Aegolius acadicus brooksi in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 23 pp.

Eder, T., & Pattie, D. 2001. Mammals of British Columbia. Lone Pine Publishing,
Vancouver, British Columbia. Pp. 296.

Hobson, K.A., & Sealy, S. G. 1991. Marine protein contributions to the diet of Northern Saw-whet Owls in the Queen Charlotte Islands: a stable isotope approach. Auk. 108: 437–440.

Martin, J.L., & Joron, M. 2003. Nest predation in forest birds: influence of predator
type and predator’s habitat quality. Oikos. 102: 641-653.

Sealy, S.G. 1998. The subspecies of the Northern Saw-whet Owl on the Queen Charlotte Islands: an island endemic and a non-breeding visitant. Western Birds. 29:21–28.

Sealy, S. G. 1999. Further data on the food items of Northern Saw-whet Owls (Aegolius acadicus brooksi) on the Queen Charlotte Islands, British Columbia. Western Birds. 300: 200-205.