Greater sage-grouse (Centrocercus urophasianus) COSEWIC assessment and status report: chapter 2

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Executive Summary

Species information

Greater Sage-Grouse (Centrocercus urophasianus) is the largest grouse in North America. It is one of two Centrocercus species; the other is the Gunnison Sage-Grouse, Centrocercus minimus, restricted to the Gunnison Valley of Colorado. Two subspecies of Greater Sage-Grouse are known from Canada: C. u. urophasianus in Alberta and Saskatchewan and C. u. phaios in the south Okanagan Valley of British Columbia. The latter form is extirpated.

Preliminary genetic analysis indicates Greater Sage-Grouse north of the Missouri River form a single population which is likely further divided into 3 sub-populations: Sage Creek (western Saskatchewan, Alberta, and northern Blaine County, Montana), Grasslands (Grasslands National Park, Saskatchewan and northern Phillips and Valley Counties, Montana), and South of the Milk River (southern Blaine, Phillips, and Valley Counties).

Distribution

Greater Sage-Grouse exhibit a near-obligate relationship with sagebrush and are found within the sagebrush range in western North America. Grouse found in Alberta and Saskatchewan are at the northern edge of the species’ range and represent less than 1% of the global population. Based on historical accounts, there has been a 90% reduction in range and substantial declines in the number of breeding locations.

Habitat

Greater Sage-Grouse inhabit the mixed grassland ecoregion of Alberta and Saskatchewan, which has been reduced significantly. Their distribution is closely associated with that of silver sagebrush. Specific attributes within the sagebrush community are required during breeding, nesting, brood-rearing and over-wintering. Herbaceous cover for nesting and brood-rearing may be limited for Greater Sage-Grouse in Canada.

Biology

Greater Sage-Grouse are long-lived and chick survival may be driving population declines. Productivity is associated with local vegetation, age and condition of the breeding female, spring precipitation, anthropogenic disturbances, and spatial distribution and density. Nest initiation rates, clutch sizes, and nesting and breeding success are normal-high compared to rates reported in the species range. This suggests that intrinsic reproductive rates and success are not factors limiting the population. However, chick survival is low and may be the demographically limiting factor.

Given their small population in Canada, Greater Sage-Grouse are susceptible to climate and stochastic events. Extended drought may exacerbate the already limited amount of herbaceous cover for nesting and brood-rearing and degrade silver sagebrush habitat. Greater Sage-Grouse are difficult to raise in captivity and are not good candidates for translocation. Currently, however, adequate gene flow exists in Canada.

Population sizes and trends

Monitoring by lek counts has occurred since 1968 and 1987 in Alberta and Saskatchewan, respectively. Survey effort and protocol has varied within and between provinces and between years. The accuracy of using lek counts to monitor abundance is questionable. Crude population estimates are made with assumptions of sex ratio, male sightability on leks and the number of occupied leks. Using lower population estimates, the number of individuals in both provinces has declined from 777 in 1996 to 450 in 2006, a 42% decline. From 1988 to 2006 the total Canadian population declined 88%. Similar results are shown for leks, which declined in number from 30 to 15 from 1996 to 2006 (50% decline).

There appears to be an essential corridor for gene flow in western Saskatchewan that connects the Alberta grouse to Saskatchewan and Montana.

Limiting factors and threats

Current population declines are likely due to an accumulation of causes but loss and degradation of habitat is thought to be the most important limiting factor. This has occurred through cultivation of rangeland for agriculture and overgrazing in the United States of America, expansions in oil and gas exploration and changes in hydrology. The effect of West Nile Virus and loss of genetic variability are not fully understood, but may have serious implications for a small population.

Special significance of the species

Greater Sage-Grouse are considered an indicator of the health of the mixed grassland ecosystem, and their range-wide declines may be cause for concern. They have high public appeal due to their unique, colourful breeding display, making them a perfect ambassador for the ecosystem they inhabit.

Existing protection or other status designations

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assessed the urophasianus subspecies of Greater Sage-Grouse as Endangered in 1998 and the phaios subspecies as Extirpated in 1997. Provincially, the Greater Sage-Grouse was listed as endangered in Saskatchewan and Alberta in 1999 and 2000, respectively. It was listed under the Species at Risk Act in 2003. Provincial representatives established a recovery team in 1997 and produced a Canadian Sage-Grouse recovery strategy in 2001. A Species at Risk compliant Recovery Strategy was compiled in 2006, outlining species biology and recovery goals.

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.