Northern saw-whet owl (Aegolius acadicus brooksi) COSEWIC update and status report: chapter 2

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Executive Summary

Species information

The brooksi subspecies of Northern Saw-whet Owl (Aegolius acadicus), sometimes called the Haida Gwaii Saw-whet Owl, is endemic to the Haida Gwaii/Queen Charlotte Islands archipelago off the northwest coast of British Columbia. Like its continental counterpart (A. a. acadicus), this is a small owl about 20 cm in length. Overall, plumage is darker than in the nominate counterpart, having an overall buffy appearance with a more mottled look on the chest. Northern Saw-whet Owls have yellow eyes, a prominent round facial disk and no ear tufts.

Distribution

Although the continental subspecies of Northern Saw-whet Owl is found across much of the southern half of Canada and much of the USA, the brooksi subspecies is endemic to Haida Gwaii/Queen Charlotte Islands.

Habitat

During the breeding season, these owls are found primarily in mature and old forest habitats at lower elevations (below 300 m), placing them in the Coastal Western Hemlock Biogeoclimatic Zone. Saw-whet owls are secondary cavity nesters, and appropriately sized cavities (>7.5 cm diameter opening) are a limiting factor across the landscape. They occur most commonly in old forest, and more in Western Hemlock and Sitka Spruce stands than in those of other tree species. Due to forest harvest, the amount of suitable habitat is declining, with an almost 13% decline in the past 10 years.  Outside the breeding season, the habitat requirements are largely unknown, but evidence suggests that some move towards coastal areas to capitalize on a rich and accessible food source, intertidal isopods and amphipods. About 2,250 km² of the islands (not all suitable habitat) are protected in the form of Gwaii Haanas National Park Reserve, Naikoon Provincial Park and 12 Wildlife Habitat Areas.

Biology

Northern Saw-whet Owls live between five and seven years, and start breeding during their first spring (one year old). The eggs are incubated and the altricial young brooded solely by the female, while the male hunts and provides food for the female and nestlings. Although much asynchrony exists between individuals in the breeding season, courtship activities tend to start in early March, and young begin fledging in June and July. Nests are in cavities excavated mostly by woodpeckers. Although there are some potential predators on Northern Saw-whet Owls on Haida Gwaii, most of these are diurnal and likely do not have a major impact on owl numbers. The brooksi subspecies differs from the acadicus subspecies by being non-migratory; it remains on Haida Gwaii year-round.

Population sizes and trends

Population sizes and trends have been calculated using estimates of density in disturbed and contiguous habitats and extrapolating these densities to the amount of appropriate habitat available across the landscape. Using these estimates, there are approximately 926 + 290 territories (breeding pairs) on the Queen Charlotte Islands and a projected decline for the next 15 years (three generations) of about 9%.

Limiting factors and threats

This subspecies is endemic to an isolated archipelago, where its populations appear to be declining in areas affected by timber harvest. Having this limited range, there is no external source population to temper a decline in the population due to decreasing habitat. The introduction of Sitka Black-tailed Deer has led to a decline in understory vegetation by browsing. This change in the forest habitat may affect songbird, rodent and invertebrate populations, all important food sources to Northern Saw-whet Owls.

Special significance of the species

This is a distinctive subspecies endemic to Canada.

Existing protection

Federally, Northern Saw-whet Owls in Gwaii Haanas National Park Reserve are protected from hunting, trafficking or possession under the Canada National Parks Act.  Provincially, the brooksi subspecies is Blue-listed. Internationally, these owls are listed under Appendix II of the Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES).

COSEWIC History

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list.  On June 5^th 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC Membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species. 

Definitions (2006)

Wildlife Species

A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and it is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.

Extinct (X)

A wildlife species that no longer exists.

Extirpated (XT)

A wildlife species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)

A wildlife species facing imminent extirpation or extinction.

Threatened (T)

A wildlife species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)^Footnotea

A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.

Not at Risk (NAR)^Footnoteb

A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.

Data Deficient (DD)^Footnotec

A category that applies when the available information is insufficient (a) to resolve a species' eligibility for assessment or (b) to permit an assessment of the species' risk of extinction.