Short-eared owl (Asio flammeus) COSEWIC assessment and status report: chapter 2

COSEWIC Executive Summary

Short-eared Owl
Asio flammeus

Species information

The Short-eared Owl, Asio flammeus (Pontoppidan), is a medium-sized owl, approximately 34-42 cm in length. Adults are cryptically coloured with a brown back and creamy-buff chest with brown streaks. The best field mark is the species’ habit of flying low over open habitat with deep, moth-like wing beats.

Distribution

Short-eared Owls are a cosmopolitan species, breeding on many continents and on many islands. In North America, they breed in arctic areas, in coastal marshes, and in interior grasslands. In winter, they generally move southward and are found in coastal areas, as well as interior grasslands, with the central Great Plains typically a centre of abundance.

Habitat

A wide variety of unforested habitats are used, including arctic tundra, grasslands, sand-sage, fallow pastures, and occasionally fields planted with row-crops. Although Short-eared Owls clearly prefer open habitats, it is thought that the primary factor influencing local habitat choice (in summer and winter) is food abundance.

Biology

Short-eared Owls are a nomadic species, with most individuals wandering widely both seasonally and annually. Individuals on islands, however, appear to show higher philopatry to breeding sites. Concentrations of Short-eared Owls occur during breeding and non-breeding at sites where rodent (typically Microtus) populations are high. Nests are placed on the ground in open habitats, and clutches of 4-7 eggs are initiated from April to June. A single brood is typically raised. Before they can fly, nestling owls typically disperse short distances from the nest site, hiding in nearby vegetation.

Population sizes and trends

The estimated global population is about 2,000,000, with 700,000 in North America and 350,000 in Canada. Christmas Bird Count data suggest that Short-eared Owls have declined at a rate of about 3% annually over the last 40 years.

Limiting factors and threats

It is important to note that there are almost no quantitative data available on the factors affecting population declines in Short-eared Owls – rather, the ideas cited below are a summary of published hypotheses.

The primary limiting factor appears to be habitat loss and alteration, especially coastal marshes and grasslands that were formerly heavily used by wintering owls, but also grasslands on the Canadian prairies and in southern Ontario. Other, secondary, factors that may contribute (to a much lesser degree) to population declines include 1) increased nest depredation (as a result of habitat fragmentation); 2) declines in prey abundance as a result of habitat changes; and 3) collisions with vehicles, utility lines, and barbed wire fences. Although organochlorines have been found in Short-eared Owl eggs, more data are needed on the prevalence and impacts of such contamination.

Special significance of the species

Short-eared Owls were formerly a common sight on the Canadian prairies and at various sites on both coasts – they are now uncommon to rare in these areas. Despite a recent increase in grassland habitat on the U.S. Great Plains (where many Short-eared Owls winter), no apparent increase has been detected in the Canadian breeding population.

Existing protection or other status designations

Based on a previous COSEWIC report (Cadman and Page 1994), Short-eared Owls were assessed as Special Concern. The Short-eared Owl is currently classified as G5 (demonstrably widespread and secure) by NatureServe. However, NatureServe provincial status designations in Canada are: Alberta (S3), British Columbia (S3B,S2N), Labrador (S3S4B), Manitoba (S3S4B), New Brunswick (S3B), Newfoundland (S3B), Northwest Territories (SNRB), Nova Scotia (S1S2B), Nunavut (SNRB), Ontario (S3S4B), Prince Edward Island (S1S2B), Quebec (S3S4), Saskatchewan (S3B,S2N), Yukon Territory (S4B). NatureServe status designations are: S1 = critically imperiled, S2 = Imperiled, S3 = Vulnerable, S4 = apparently secure, and SNR = Not ranked).

Short-eared Owls are protected under the Migratory Bird Treaty Act (Federal Register 2006) as well as under a large number of Provincial Wildlife acts (e.g., Ontario Fish and Wildlife Conservation Act, and the Act Respecting the Conservation and Development of Wildlife in Quebec). Short-eared Owls are also listed as Endangered, Threatened, or a Species of Concern in many U.S. states and as a Species of Conservation Concern by the U.S. Fish and Wildlife Service.

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, theSpecies 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) Footnote1
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) Footnote2
A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.

Data Deficient (DD) Footnote3
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.

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