Canada warbler COSEWIC assessment and status report: chapter 2

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COSEWIC Executive Summary

Species information

The Canada Warbler (Wilsonia canadensis) is a small, brightly coloured passerine. The males are typically more brightly coloured than the females and immatures, with blue-grey upperparts and tail contrasting with a yellow throat and breast. In both sexes, black stripes form a collar on the breast, although it is less defined in the females. The adults keep the same plumage year round. The plumage of the immatures is similar to that of the adults, but generally duller.

Distribution

Approximately 80% of the Canada Warbler’s global breeding range is located in Canada, where it breeds in all provinces and territories except Nunavut and Newfoundland and Labrador. It winters in northwestern South America.

Habitat

The Canada Warbler uses a wide range of deciduous, coniferous and mixed forests, with a well-developed shrub layer and a structurally complex forest floor. It is most abundant in moist, mixed forests. It also occurs in riparian shrub forest on slopes and in ravines, in stands regenerating after natural and anthropogenic disturbances and in old-growth forests with canopy openings and a well-developed shrub layer. In its wintering range, the Canada Warbler uses primarily mature cloud rainforests located at an altitude of 1,000 to 2,500 m, as well as second-growth forests, forest edges, coffee plantations, agricultural field edges and semi-open areas.

Canada Warbler habitat is believed to be in decline primarily in its wintering range, where up to 95% of the primary mountain forests have been converted to agriculture since the 1970s. Habitat loss has also been observed in the eastern part of its breeding range, where wet forests have been drained for urban development and forest converted to agricultural land.

Biology

The Canada Warbler is typically monogamous and lays four to five eggs. Incubation usually lasts about 12 days. The chicks remain in the nest for 10 days, and are dependent on parents for two to three weeks after they leave the nest.

Population sizes and trends

The Canadian population of Canada Warbler is estimated at roughly 2.7 million individuals. Breeding Bird Survey (BBS) data for Canada suggest that the species has declined by 4.5%/year between 1968 and 2007, which amounts to a loss of approximately 85% of the population during that period. Between 1997 and 2007, the species declined by 5.4%/year, which corresponds to a decline of 43% of the population in the most recent 10-year period. These declines are most evident in the eastern portions of the breeding range, where the majority of the population occurs. Other survey methods also report declines in the Canada Warbler population.

Limiting factors and threats

The factors responsible for the decline of the Canada Warbler have not been identified. Habitat loss and degradation on the wintering range are thought to be the most likely factors. In Canada, habitat loss due to conversion of swamp forests in the east, agricultural activities and road development in the boreal forest in the western part of the range and possibly a decrease in spruce budworm (Choristoneura fumiferana) outbreaks in eastern forests since 1970 may have also contributed to the decline.

Special significance of the species

Eighty-five percent of the global breeding population of Canada Warbler occurs in Canada. For this reason, Canada has a major responsibility for the conservation of this species.

Existing protection or other status designations

Canada Warbler adults, nests and eggs are protected in Canada under the Migratory Birds Convention Act, 1994. It is considered a high-priority species by Partners in Flight in Canada and the United States.

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) ^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.

Canadian Wildlife Service

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