Ferruginous hawk (Buteo regalis) COSEWIC assessment and status report: chapter 2

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Executive Summary

Species information

The Ferruginous Hawk (Buteo regalis; French: Buse rouilleuse) is a large, open country, diurnal raptor that occurs in western North America. In many respects, the Ferruginous Hawk is similar to the Golden Eagle. The Ferruginous Hawk has broad, long wings with rounded tips and a fan-shaped tail. Two colour phases occur; a more common pale phase in which hawks have brown upper parts (with extensive orange-cinnamon and white markings on the shoulders and back), white underparts with brown streaks and a white to greyish tail. The less common dark-phased birds have dark brown plumage (some feathers are edged with cinnamon) and a white, pinkish or grey tail.

Distribution

The Ferruginous Hawk is found in the grasslands, shrublands and deserts of the western United States and western Canada. In Canada it breeds in southern Alberta, southern Saskatchewan and southern Manitoba; a few pairs have nested in southern British Columbia, at least historically.

Canada holds about 10% of the world’s breeding distribution of the Ferruginous Hawk and that range is contracting; it now occupies only 48% of its historical range in Canada.

Habitat

East of the Rocky Mountains, the Ferruginous Hawk is strongly dependent on native grasslands, which have been subject to degradation, conversion and fragmentation by urbanization, farming and industrial development. West of the Rockies, grasslands and shrub-steppe arid areas are heavily used by Ferruginous Hawks. On the other hand, aspen parkland, montane forests and areas of intensive agriculture are avoided. The distribution of the Ferruginous Hawk retracted at the northern edge of the range in Canada during the early 1900s because of agriculture and invasion of trembling aspen into the remaining mesic native prairie grassland due to fire suppression. Ferruginous Hawks are very sensitive to habitat loss and are considered a native grassland specialist.

Biology

The Ferruginous Hawk is wary of humans, as well as being secretive, often roosting on the ground. Thus, it is much less conspicuous than other sympatric hawks such as Swainson’s Hawk, making it more difficult to monitor its populations. The Ferruginous Hawk uses a wide variety of structures for nesting, including cliffs, trees, utility structures, farm buildings, abandoned farm machinery, haystacks and artificial platforms. Apparently monogamous (though sometimes three birds are seen together), the Ferruginous Hawk is territorial and breeds for the first time at two years of age. Clutch size ranges from 2-8 eggs. The Ferruginous Hawk is a ‘’sit-and-wait’’ predator and up to 5-10 hawks have been observed at prairie dog towns. East of the Rockies, the Ferruginous Hawk depends on a keystone prey species, the Richardson’s ground squirrel, whereas west of the Rockies, it preys on jackrabbits, prairie dogs and pocket gophers.

Population sizes and trends

Ferruginous Hawks now occupy about half of their historical range in Canada. In Alberta, the population was estimated at 618 ± 162 pairs in 2005, substantially lower than earlier estimates. Whether this is due to an actual decline in numbers in Alberta or improvements in survey techniques in unknown but it is now thought that the population has been at a low since 2000. In Saskatchewan, the population had previously been roughly estimated at between 300-500 pairs based on known nest localities, site occupancy and extrapolation from small study areas. A 2006 survey found 278 nests in Saskatchewan in a search that covered all historical nesting sites and about 12% of the species’ range there. In Manitoba, the latest population estimate (2005) is 42 pairs. The entire Canadian population is probably about 1200 pairs, about half of what was estimated in 1998.

Evidence for recent declines in Ferruginous Hawk populations comes from hawkwatch counts while Breeding Bird Survey data suggest a stable or increasing population, although the latter have many deficiencies for monitoring trends in raptor populations. The latest analysis of migration counts from western North America (1977-2001) demonstrated significant declines at four of the six hawkwatch sites analyzed. At two of these sites passage rates increased until the early to mid-1990s, then decreased; long-term declines have occurred at the other two sites.

Like many other raptor species, population parameters (e.g., reproductive success) of Ferruginous Hawks fluctuate according to prey abundance and availability. Natural fluctuations in the populations of ground squirrels are mirrored in the breeding parameters of Ferruginous Hawks. Although populations may appear healthy in ranching areas of Alberta, habitat for the species is saturated and there is quite strong evidence that the species is declining.

Limiting factors and threats

Limiting factors in order of importance are likely increased human disturbance (particularly at nest sites), decreased prey abundance (Richardson’s ground squirrel), loss and/or declines in habitat quality of native prairie grassland, interspecific competition (from other Buteo hawk species), and oil and gas exploration.

Special significance of the species

The Ferruginous Hawk is a native prairie grassland specialist and is one of the least adaptable of several other species of prairie hawks.

Existing protection or other status designations

The Ferruginous Hawk was listed as Threatened by COSEWIC in 1980, but was downlisted to Special Concern in 1995 by COSEWIC and is on Schedule 3 of the federal Species at Risk Act (SARA 2002). It is listed as Endangered under the Alberta Wildlife Act and as Threatened under the Manitoba Endangered Species Act. The species is not listed in Saskatchewan.

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.