Western screech-owl (Otus kennicottii) COSEWIC assessment and status report: chapter 2

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Executive Summary

Species information

The Western Screech-owl, Otus kennicottii, is a small, grey-brown owl with streaked plumage and ‘ear tufts’. Its appearance is very similar to the Eastern Screech-owl, which was considered conspecific with the Western Screech-owl until 1983. As the ranges of the two species do not usually overlap in Canada misidentification is unlikely. There is confusion over the number of subspecies of Western Screech-owl that occur in North America. This report, however, follows the most current source, which considers that there are two subspecies in Canada, Otus kennicottii kennicottii and Otus kennicottii macfarlanei.

Distribution

The Western Screech-owl is found in western North America from southern Alaska to central Mexico. In Canada, the species occurs only in British Columbia (BC) in two regions: along the coast of BC including Vancouver Island, but excluding the Queen Charlotte Islands (O. k. kennicottii ), and in the southern interior part of the province (O. k. macfarlanei ), with most of the interior birds being found in the Okanagan Valley.

Habitat

In Canada the owl is found at lower elevations generally in wooded environments that are often in riparian (creek-side) zones, although it is does not seem to be tightly linked to a particular type of woodland. It can also be found in treed urban and suburban environments, and at the edge of forested habitats close to open wetlands or fields. Along the coast it seems to be mostly found in either coniferous or mixed (deciduous or coniferous) forests, whereas interior birds seem to be found more frequently in deciduous or mixed forests. During the daytime it roosts in either coniferous or deciduous trees.

Biology

The Western Screech-owl is a nocturnal, non-migratory species that is territorial year-round. It has been known to live up to 11 years in the wild, but its average life-span is not known. It nests in natural cavities in trees generally made by large woodpeckers, or in nest boxes. They seem to be opportunistic in their choice of prey. Their diet includes various species of mammals, fish, birds, insects and other invertebrates. The owl is preyed upon by several predators including large owls such as the Barred Owl (Strix varia). The Barred Owl has only become common in western BC in the last decade or two, thus it is a new predator for the Western Screech-owl.

Population sizes and trends

The population size and trends of the Western Screech-owl in Canada are difficult to estimate because there are few published sources of information on this subject. Given that the coastal subspecies appears to be relatively common on most of Vancouver Island and that it also occurs along a large stretch of the mainland coast, the upper estimate for this population might be as high as 10,000 birds. However, a lower estimate of 3,000 birds may be more realistic because populations in the southern populated parts of the coast appear to be declining, and it is not known if the rest of the coastal subspecies is declining as well.

A rough estimate for the very small interior population is 50 to 200 birds. Most sightings, and all breeding records, come from the Okanagan Valley, but individuals are also found rarely elsewhere in the southern interior. The subspecies seems to have always been rather uncommon and its population is now very small.

Limiting factors and threats

Along the south coast of BC, declines in Western Screech-owl populations have occurred at the same time as strong increases in the Barred Owl population. The evidence for a direct link between these two phenomena is mostly anecdotal, but it is repeated by numerous sources. Serious habitat loss is occurring in the southern interior of BC where the valley bottomlands preferred by screech-owls are more likely to be developed than other habitats. Also, Western Screech-owls require trees that are large enough to hold a nest cavity within which they can breed; thus some forestry practices in urban and wilderness situations may negatively impact this species.

Special significance of the species

The Western Screech-owl has been considered an indicator species for healthy riparian ecosystems throughout most of its range. Its dependence on older trees for roosting and nesting cavities and position near the top of the food chain make it an ideal choice for an umbrella species in multispecies conservation plans.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) determines the national status of wild species, subspecies, varieties, and nationally significant populations that are considered to be at risk in Canada. Designations are made on all native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fish, lepidopterans, molluscs, vascular plants, lichens, and mosses.

COSEWIC Membership

COSEWIC comprises representatives from each provincial and territorial government wildlife agency, four federal agencies (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biosystematic Partnership), three nonjurisdictional members and the co-chairs of the species specialist groups. The committee meets to consider status reports on candidate species.

Definitions

Species

Any indigenous species, subspecies, variety, or geographically defined population of wild fauna and flora.

Extinct (X)

A species that no longer exists.

Extirpated (XT)

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

Endangered (E)

A species facing imminent extirpation or extinction.

Threatened (T)

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

Special Concern (SC)^Footnotea

A species of special concern because of characteristics that make it particularly sensitive to human activities or natural events.

Not at Risk (NAR)^Footnoteb

A species that has been evaluated and found to be not at risk.

Data Deficient (DD)^Footnotec

A species for which there is insufficient scientific information to support status designation.

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.

The Canadian Wildlife Service, Environment Canada, provides full administrative and financial support to the COSEWIC Secretariat.