Greater sage-grouse (Centrocercus urophasianus) COSEWIC assessment and status report: chapter 5
Habitat
Habitat requirements
Greater Sage-Grouse are associated with sagebrush habitat at all times of the year and exhibit specific requirements for breeding, nesting, brood-rearing, and wintering (Braun et al. 2005). In Canada, they inhabit the silver rather than big sagebrush (A. tridentata) dominated community that is characteristic of most of the species’ range in the United States. This community exhibits less canopy cover and is lower in quality and carrying capacity (Kerwin 1971; Aldridge and Brigham 2002; Adams et al. 2004). Silver sagebrush is associated predominantly with alluvial landforms, which are characterized by deep, productive soil and occasional flooding (Thorpe 2002; McNeil and Sawyer 2003; Adams et al. 2004; Jones et al. 2005). Grasses are predominant in this mixed grassland ecoregion and include needle-and-thread grass (Hesperostipa comata), june grass (Koeleria macrantha), blue grama (Bouteloua gracilis) and western wheatgrass (Pascopyrum smithii) (Aldridge and Brigham 2003). In Alberta, dominant forbs are clover (Trifolium spp.), vetch (Astragalus spp.) and common dandelion (Taraxacum officinale) (Aldridge and Brigham 2003). Dominant forbs in southwestern Saskatchewan were pasture sage (Artemisia frigidus), scarlet mallow (Sphaeralcea coccinea), prairie selaginella (Selaginella densa) and moss phlox (Phlox hoodii) (McAdam 2003). Dominant forbs in the vicinity of Grasslands National Park are scarlet mallow, prairie selaginella, and common knotweed (Polygonum aviculare) (Thorpe et al. 2005).
Breeding
Leks typically have less shrub and herbaceous cover and are often situated on broad ridge tops, knolls, grassy swales, dry lake or creek beds, and burned areas (Scott 1942; Braun et al. 1977; Harris and Weidl 1988; Schroeder et al. 1999). Dense cover is found adjacent to breeding grounds (Call and Maser 1985). Lek sizes range from 0.3 to 1.1 hectares in Saskatchewan (Kerwin 1971) and are predominantly in areas of native vegetation (Thorpe et al. 2005). Leks in southern Alberta are associated with alluvial stands of silver sagebrush and western wheatgrass (McNeil and Sawyer 2001). In Alberta, leks were frequently lower than surrounding areas and adjacent to water (Aldridge 2000). In Saskatchewan no significant association was detected between lek occupancy and the amount of naturally occurring water sources (McAdam 2003).
Nesting
Nests are situated almost exclusively under sagebrush (Patterson 1952; Klebenow 1969; Braun et al. 1977; Connelly et al. 1991; Musil et al. 1994) and those associated with big sagebrush have higher nest success (Connelly et al. 1991). In Alberta, over 80% (n = 119) of nests were under silver sagebrush (Aldridge and Brigham 2002; Aldridge 2005).
The basic requirement of a nest site is concealing vegetation (Patterson 1952). Nest selection and success is positively associated with shrub and sagebrush cover (Klebenow 1969; Wallestad and Pyrah 1974; Gregg et al. 1994; Aldridge and Brigham 2002; Watters et al. 2002; Aldridge 2005; Holloran et al. 2005) shrub height (Wallestad and Pyrah 1974; Gregg et al. 1994; Delong et al. 1995; Aldridge and Brigham 2002; Watters et al. 2002), grass height (>18 cm) (Klebenow 1969; Gregg et al. 1994; Delong et al. 1995; Aldridge 2005) and residual grass height and cover (Holloran et al. 2005). Lateral forb cover was a predictor of hatching success for both artificial and natural nests in Alberta (Aldridge and Brigham 2001; Watters et al. 2002).
Brood-rearing
Forage and cover are basic habitat requirements for brood-rearing. Early brood-rearing sites tend to be in sagebrush habitat close to nest areas. However, broods shift to more mesic sites later in the season as forbs begin to desiccate (Klebenow 1969; Wakkinen 1990; Fischer et al. 1996a). Kerwin (1971) noted broods in Grasslands National Park, Saskatchewan, selected meadows rich in forbs as summer progressed. This shift to mesic sites in late brood-rearing was not reported for 15 females radio-marked in southern Alberta (Aldridge and Brigham 2002). In southern Alberta, females with broods selected areas with greater sagebrush cover (Aldridge and Brigham 2002), contrary to studies where big sagebrush was the dominant shrub cover (Klebenow 1969; Dunn and Braun 1986). Authors suggest mesic brood-rearing habitat rich in forb cover may be limited in southeastern Alberta (Aldridge and Brigham 2002; Aldridge 2005; Aldridge and Boyce 2007).
Winter
Wintering habitat is relatively similar throughout the species range (Connelly et al. 2000a). Greater Sage-Grouse have a near-obligate relationship with sagebrush for forage and cover during winter (Eng and Schladweiler 1972; Wallestad et al. 1975) and distribution is limited by topography and availability of sagebrush above snow (Beck 1977; Hupp and Braun 1989). Due to habitat selection for increased sagebrush canopy cover and height (Eng and Schladweiler 1972; Wallestad et al. 1975; Aldridge et al. 2004), preferred winter sites include southwest slopes, draws, swales and wind-swept ridges (Beck 1977; Hupp and Braun 1989).
Habitat trends
Greater Sage-Grouse habitat in Canada is associated with silver sagebrush (McNeil and Sawyer 2001; Jones et al. 2005). Silver sagebrush is largely restricted to the mixed grassland ecoregion. Cultivation, and oil and gas development are primarily responsible for elimination of native vegetation in the mixed grassland ecoregion of Saskatchewan and Alberta (Hammermeister et al. 2001; Braun et al. 2002; Lungle 2006).
Within Saskatchewan, silver sagebrush is common south of the Cypress Hills and Wood Mountain, and from the Cypress Hills north to the South Saskatchewan River (Thorpe 2002). The amount of mixed grassland remaining in Saskatchewan is 2.7 million ha or approximately 31% of the ecoregion (Hammermeister et al. 2001; Nernberg and Ingstrup 2005). McAdam (2003) reviewed land use changes within 3.2 km of leks in Saskatchewan using aerial photographs from 1955, 1971, 1981, and 1996. Cultivation of native vegetation at occupied leks increased from 5.4 ha/year (1955 to 1971) to 24.3 ha/year (1971 to 1996). Similarly, cultivation surrounding abandoned leks increased from 25.5 ha/year to 63.7 ha/year (McAdam 2003). Thorpe et al. (2005) reported no net increase in cultivation at leks in Saskatchewan between 1981 and 2003.
In Alberta, only 2.6 million ha of mixed grassland remain, representing 54% of the historic extent (Nernberg and Ingstrup 2005). From the late 1970s to present, oil and gas development has been primarily responsible for elimination and fragmentation of native grassland vegetation in Alberta (Braun et al. 2002).
Considerable land ownership south of the Saskatchewan border in Montana is federal (Bureau of Land Management) and primary land use is livestock grazing (Carlson pers. comm. 2006). Rangeland is still relatively intact. However, significant areas of rangeland in northeastern Montana have been converted for agriculture or oil and gas development (Connelly et al. 2004; Carlson pers. comm. 2006).
Habitat protection/ownership
In Alberta, 75% of all occupied leks occur on Crown land. Thirty-three percent of remaining mixed prairie grassland in Alberta occurs on private land (Nernberg and Ingstrup 2005). Of 35 inactive and active leks, only 5 occur on private land (Nicholson pers. comm. 2006). Federal protection is afforded for one lek on the One-Four Agricultural Research Station, which has been inactive since 1976 (Nicholson pers. comm. 2006). Recommendations and guidelines are made by Alberta Fish and Wildlife to reduce the impact of oil and gas exploration, particularly in important breeding habitat. However, there is no current legislation that commits Alberta Public Lands or the Alberta Energy Utility Board to follow these recommendations (Braun et al. 2002).
In Saskatchewan, 66% of occupied leks occur in Grasslands National Park. The park encompasses 497 km² in both the East and West Blocks and may eventually cover up to 900 km² along the Canada-U.S. border (Parks Canada 2005). This additional acquisition will protect a known existing occupied lek and a second lek that may or may not be occupied (Fargey pers. comm. 2006). Another lek monitored by Grasslands National Park of Canada exists on Val Marie Prairie Farm Rehabilitation Administration (PFRA) pasture, which is afforded federal protection by the Species at Risk Act and the Representative Areas Network (RAN) (McAdam pers. comm. 2006). Occupied and abandoned leks monitored by Saskatchewan Environment are on provincial land protected by the Wildlife Habitat Protection Act (WHPA) or PFRA pastures (McAdam pers. comm. 2006).
Landscape level modelling has shown that good quality “source” habitat for nesting and brood-rearing is limited (Aldridge and Boyce 2007). Much of the habitat suitable for Greater Sage-Grouse in Canada is on provincial or federal crown lands, and with favourable management practices, can support Canadian populations (Lungle 2006).
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