Spotted owl (Caurina subspecies) COSEWIC assessment and status report: chapter 2

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COSEWIC Executive Summary

Species information

The Northern Spotted Owl (Strix occidentalis caurina) is the subspecies of Spotted Owl that occurs in Canada. It is a medium-sized owl averaging 45 cm long and 90 cm wingspan. It is a dark-plumaged owl with dark eyes, lighter facial discs and no ear tufts. It is genetically distinct from other subspecies and from its co-existing congener the Barred Owl, even though hybridization occurs occasionally.

Distribution

The Spotted Owl occurs in western North America from southwestern British Columbia to Mexico. The Northern Spotted Owl subspecies occurs from the southwest mainland of British Columbia through western Washington, western Oregon and the coast ranges of northern California. The entire Canadian population of the Northern Spotted Owl occurs in about 32,800 km² in the southwest mainland of British Columbia.

Habitat

The Northern Spotted Owl occurs in coniferous forests with an uneven-aged, multi-layered canopy that includes numerous large trees with broken tops, deformed limbs and large cavities, and numerous large snags and accumulations of logs and downed woody debris. Wildlife trees such as broken large diameter trunks, cavities in large trees, or old stick nests of other birds are used for nests. A wider range of habitat is used for foraging compared to nesting. It has a narrow thermal neutral zone (e.g., has a low temperature-range tolerance). Habitat has declined since European settlement, continues to decline today and is forecast to decline for another 20 years. Most currently active sites are within protected areas or are protected by special government orders, but government-approved logging continues within some active sites.

Biology

The Northern Spotted Owl is a long-lived bird with low reproductive potential. It is normally monogamous, resident, lays one or two eggs and fledges one or two young when it breeds. Pairs do not typically nest every year. Young leave the nest in British Columbia from 9-26 June. Fledged young remain near the nest through August and to late September before dispersing. Mortality of juveniles during dispersal is very high. Main foods in British Columbia are northern flying squirrel and Bushy-tailed woodrat. Home ranges in British Columbia are about 2000 to 3000 ha.

Population sizes and trends

Survey effort was almost non-existent before 1985. Inventory began in 1992 and trends were monitored between 1992 and 2001. Intensive survey effort continued from 2002 through 2006. Total Canadian population was estimated to be about 500 pairs prior to European settlement, < 100 pairs by 1991, and < 30 pairs by 2002. Recent surveys found 17 active sites with 25 birds in 2004, 17 sites with 24 birds in 2005, 14 sites with 17 birds in 2006, and 14 sites with 19 birds in 2007. Without increased habitat protection and direct population augmentation, extirpation is now seemingly inevitable and appears likely to occur by 2012 if present trends continue.

Limiting factors and threats

Limiting factors include low annual productivity, high juvenile mortality, lack of recruitment in recent years, very low densities and large distances between active sites, loss and degradation of habitat, presumed reduced emigration from the USA, and competition from Barred Owls. Threats include continued degradation of habitat by logging and human development, degradation of habitat by wildfires and insect outbreaks, hybridization with Barred Owls, and increasing predation from raptors that favour more fragmented forests.

Special significance of the species

The Northern Spotted Owl is among the most studied owl species in the world and is an environmental icon in Canada and the USA. The Northern Spotted Owl is a high-level predator with specialized habitat requirements. It is at the top of the food chain in some late-successional coniferous forest ecosystems on the west coast of North America.

Existing protection or other status designations

Most active sites are protected within Provincial Parks or other protected areas. The Spotted Owl Management Plan covers 363,000 ha of land (about half of which is protected in parks) in 19 Special Resource Management Zones (SRMZs) specifically managed as habitat for Spotted Owls. Additional areas are protected as temporary Matrix areas (8 areas) which will be phased out over 50 years, or by Wildlife Habitat Areas recently created to conserve nine sites, eight of which were already SRMZs. A newly announced 5-year Spotted Owl Management Plan hopes to maintain this species in Canada. A national Recovery Strategy has been prepared and has now been posted on the SARA public registry.

The Northern Spotted Owl is on the British Columbia Red List and is protected in British Columbia under the BC Wildlife Act. Habitat may also be protected by Identified Wildlife Management Strategy provisions under the Forest and Range Practices Act, and Old-Growth Management Areas. In Canada, it is listed on Schedule 1 of SARA and COSEWIC has assessed it as Endangered in 2000.

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, 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 (2008)

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 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)*

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)**

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

Data Deficient (DD)***

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.

* Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.
** Formerly described as “Not In Any Category”, or “No Designation Required.”
*** Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” (insufficient scientific information on which to base a designation) prior to 1994. Definition of the (DD) category revised in 2006.

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