Rusty blackbird (Euphagus carolinus) COSEWIC assessment and status report: chapter 2

COSEWIC Executive Summary

Rusty Blackbird
Euphagus carolinus

Species information

The Rusty Blackbird (Euphagus carolinus) is a medium-sized passerine with a slightly rounded tail that is as long as its wings. Both sexes have pale yellow eyes and a black, slightly curved bill. During the breeding season, the adult male is uniformly black, with a faint greenish gloss to its body and slight violet gloss to its head and neck. The female is brownish grey with no gloss. In winter, the plumage of both sexes is more rust-colored. In the western provinces, the Rusty Blackbird can easily be confused with the Brewer’s Blackbird (E. cyanocephalus), which has similar plumage and morphology.

Distribution

The Rusty Blackbird has a breeding range of 7.6 million km², including most Canadian provinces and territories, the state of Alaska, several Great Lakes states and most New England states. The winter range of the Rusty Blackbird includes most of the mid- to eastern states of the United States, although it winters irregularly in the southern part of most Canadian provinces.

Habitat

The breeding habitat of the Rusty Blackbird corresponds closely to the boreal forest. Within this biome, its habitat is characterized by forest wetlands, such as slow-moving streams, peat bogs, sedge meadows, marshes, swamps, beaver ponds and pasture edges. In winter, it occurs primarily in damp woodlands and cultivated fields. The primary cause of habitat loss for the Rusty Blackbird, particularly in its winter range, is the conversion of wetland for agriculture and urban development.

Biology

Rusty Blackbirds are typically monogamous and nest in isolated pairs on the margins of wetlands. The nests are built by the female and are located over or near water in riparian vegetation. Only the female incubates the eggs, which generally number 3 to 6. Incubation lasts 14 days, and usually begins as soon as the first egg is laid. The chicks remain in the nest for approximately 13 days.

Population size and trend

The Canadian population, which includes approximately 70% of the global breeding population, is estimated at between 110,400 and 1.4 million individuals. Several indices suggest that the Rusty Blackbird population has declined significantly over the last 40 years. Long-term trend analyses based on Christmas Bird Counts showed a decline of -5.1%/year since 1966. At this rate of decline, the population would have decreased by approximately 85% since the mid-1960s. Short-term analyses based on the same survey methods show an annual rate of decline of -2.1% between 1994 and 2003. At this rate, the population would have decreased by 18.3% over the last 10 years.

Limiting factors and threats

The most serious threats to the Rusty Blackbird are thought to be the conversion of the Mississippi Valley flood plain forests, the species' primary habitat in the winter range, to agricultural land and urban zones and bird control programs in the southeastern United States that have occurred since the 1970s.

Special significance of the species

Seventy percent of the Rusty Blackbird’s breeding range is located in Canada, so it is considered a species for which Canada has a major responsibility in terms of conservation.

Existing protection or other status designations

For North America as a whole, the Rusty Blackbird is considered apparently secure. The Rusty Blackbird has no protection in Canada under the Migratory Birds Convention Act (1994). Blackbirds are considered pests in Canada and the United States, and so the Rusty Blackbird can be killed during control programs for nuisance birds.

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 5th 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 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.

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