Greater sage-grouse (Centrocercus urophasianus) COSEWIC assessment and status report: chapter 6
Biology
Life cycle and reproduction
Leks are traditional areas where male Greater Sage-Grouse congregate in spring to jockey for the principal mating position (Scott 1942). A sub-dominant male, positioned near the dominant male at the centre of the lek is the primary competitor in mating. These 2 males obtained 74% (n = 174) of copulations in Wyoming (Scott 1942). Although yearling males are sexually mature, they surround the dominant and sub-dominant males and rarely breed (Schroeder et al. 1999).
Females arrive on leks later than males and attend for 2-3 days until they have successfully mated. Mean date of peak female lek attendance in southeastern Alberta occurred 5 April ± 0.9 days (Aldridge and Brigham 2001). Females fly or walk directly to the dominant male, seemingly indifferent to displays by other males on the lek (Scott 1942; Dalke et al. 1963), and solicit copulation by squatting, spreading their primaries on the ground and slightly lifting their wings (Schroeder et al. 1999). Hybridization of Greater Sage-Grouse with the sympatric Sharp-tailed Grouse (Tympanuchus phasianellus) has been documented in Alberta and Saskatchewan and is not uncommon across the species’ range (Aldridge et al. 2001).
Nesting tends to be associated with sagebrush habitat within 5 km of leks (Holloran and Anderson 2005), but has also occurred > 15 km from breeding grounds (Wakkinen et al. 1992; Holloran and Anderson 2005). Mean distance travelled from leks to nests in southern Alberta was 4.7 + 0.7 km (n = 20), which falls within the range reported in other studies (Aldridge and Brigham 2001).
Mean nest initiation date in southeast Alberta was 3 May (range 27 April to 9 May, n = 20) and 7 June for renesting (range 29 May to 19 June, n = 5) (Aldridge and Brigham 2001). Females reach sexual maturity at 1 year. Bergerud (1988) suggested that some yearling females do not make nesting attempts. However, all females radio-marked in Washington (n = 129) and Alberta (n = 20) attempted nesting (Schroeder 1997; Aldridge and Brigham 2001), and research on follicular development indicated that 91-98% of females laid eggs in the previous season (Dalke et al. 1963; Braun 1979). Reported nest initiation rates range from 68% to 100% (Schroeder et al. 1999).
Incubation lasts 25 to 29 days (Schroeder 1997; Aldridge and Brigham 2001) and mean clutch size varies from 6.0 to 9.5 throughout the range of the species (Connelly et al. 2000a). Evaluation of DNAextracted from eggshell membranes and embryos, has shown the sex ratio at hatch in southern Alberta is biased towards females (57%, n = 507) (Bush 2004). In Alberta, mean hatch date of successful nests occurred 5 June ± 4.6 days (n = 12) (Aldridge and Brigham 2001). Similarly estimated hatch dates in Saskatchewan were within the first 2 weeks of June (Kerwin 1971). Nest success is typically between 30-60% (Schroeder et al.1999).
In Alberta all tracked females initiated clutches, and clutch size (8.0 + 0.4 eggs) was at the high end of the range for the species (Aldridge and Brigham 2001). Nest success rates were within the normal range of rates reported with 46% (n = 19) and 35% (n = 40) for 1998-1999 and 2001-2003, respectively (Aldridge and Brigham 2001; Aldridge 2005). Breeding success (55%) was also within the normal range, suggesting that reproductive rates and success are not factors limiting this population (Aldridge and Brigham 2001). Chick survival from hatch to 8 weeks was low for 1998-1999 (14-23%, n = 88) and 2001-2003 (12%, n = 41) and may be an important factor limiting the population (Aldridge and Brigham 2001; Aldridge 2005).
Productivity is associated with local vegetation (see Habitat: nesting), age and condition of the breeding female, spring precipitation, anthropogenic disturbances, and spatial distribution and density. Adult females tend to lay larger clutches (Wallestad and Pyrah 1974, Schroeder et al. 1999) and have greater nesting and breeding success than yearling females (Swenson 1986; Bergerud 1988; Aldridge and Brigham 2001; Gregg et al. 2006). Nest predation rates in Wyoming increased with association to leks or other nests (Holloran and Anderson 2005). However, nest success of artificial nests in Alberta was unrelated to distance from leks (Watters et al. 2002). Nest success rates vary as a function of habitat quality (Gregg et al. 1994; Watters et al. 2002; Crawford et al. 2004) and precipitation in spring and summer (Aldridge 2005; Holloran et al. 2005).
Greater Sage-Grouse are generally in excellent physiological condition in winter and inColoradothey gain weight on an exclusive diet of sagebrush (Beck and Braun 1978; Remington 1983). Adult females experience low mortality over winter (Connellyet al. 2000b; Hausleitner 2003; Aldridge et al. 2004). Apparent winter survival rates of radio-marked adult females in southeastern Alberta were 88% (n=16) and 73% (n=15) in 2002/03 and 2003/04, respectively (Aldridge et al. 2004). This, compared to apparent spring to fall survival rates, estimated at 57% (Aldridge and Brigham 2001). Apparent winter survival rates were much lower for juveniles in this study: only 3 of 7 survived the winter (Aldridge et al. 2004). Although the sample size is small, this result suggests that juvenile survival mightbe an important factor contributing to the low recruitment rates in Alberta (Aldridge et al. 2004).
Predation
Predation may be a factor limiting nest success (Gregg et al. 1994) and annual population recruitment (Autenrieth 1981, 1986; Crawford et al. 2004). Habitat alteration may result in a loss of concealment cover for grouse or change in predator community (Bowman and Harris 1980; Johnson et al. 1996; Connelly et al. 2000a; Aldridge and Brigham 2003; Crawford et al. 2004). Raccoons (Procyon lotor), striped skunks (Mephitis mephitis), coyotes (Canis latrans), and red fox (Vulpes vulpes) have all increased on the Canadian prairies in the last half-century (Gudmundson 1996; Aldridge and Brigham 2003). Predation may be the proximate cause of mortality for grouse in poor body condition due to parasites/diseases or climatic factors (Atkinson and Van Riper III 1991; Hudson and Dobson 1991).
For many grouse species, nest predation is an important reason for reduced productivity (Reynolds et al. 1988).In Bergerud’s (1988) summary of nest success and predation rates for 9 species of grouse, Greater Sage-Grouse showed the lowest nest success (35%) and the highest rates of nest predation (47%). Alternatively, Connelly et al. (2000a) reported most nest success rates to be > 40%, indicating predation is not a significant limiting factor. Nest success rates in Alberta (35-46%) are within ranges reported for the species (Aldridge and Brigham 2001; Aldridge 2005). Nest predation in Wyoming decreased with increasing distance from leks and other nests suggesting predators concentrate their search effort (Holloran and Anderson 2005). Common nest predators in Canada include Richardson’s ground squirrels (Spermophilus richardsonii), badgers (Taxidea taxus), Black-billed Magpies (Picahudsonia), American Crows (Corvus brachyrhynchos), weasels (Mustela spp.), raccoons, striped skunks, and red fox (Harris and Weidl 1988; Watterset al.2002; Aldridge and Brigham 2003).
Annual recruitment may be limited by survival of Greater Sage-Grouse from hatch to the following breeding season (Crawford et al. 2004). Survival rates to 8 weeks and over winter in Alberta are low at 12-23%, and 43%, respectively, resulting in low annual recruitment (Aldridge and Brigham 2001; Aldridge et al. 2004; Aldridge 2005). American Kestrels (Falco sparverius), Merlins (F. columbarius), Northern Harriers (Circus cyaneus), and weasels have been known to prey upon juveniles (Schroeder et al. 1999).
Greater Sage-Grouse are long-lived compared to other Tetranonids and predation does not limit annual survival of breeding-aged birds (Connelly et al. 2000a; Connelly et al. 2004; Crawford et al. 2004). Apparent annual female survival in southeastern Alberta was 43-50%, somewhat lower than range-wide estimates (Aldridge et al. 2004). Avian predators of adults in Canada may include Golden Eagles, Gyrfalcons (Falco rusticolus), Great Horned Owls (Bubo virginianus), Cooper’s Hawk (Accipiter cooperii), Northern Goshawk (A. gentilis), Swainson’s Hawk (Buteo swainsoni), Red-Tailed Hawk (B. jamaicensis), Ferruginous Hawk (B. regalis) (Schroeder et al. 1999) and Northern Harriers (Fletcher et al. 2003). Bobcat, mink (Mustela vison), coyote, red fox and swift fox (Vulpes velox) are potential mammalian predators (Schroeder et al. 1999; ASGRAG 2005).
Dispersal / migration
Greater Sage-Grouse exhibit some philopatry to natal leks, although dispersal is not uncommon (Dunn and Braun 1985). Dispersal rates are similar in males and females (Dunn and Braun 1985, Bush pers. comm. 2006), although female dispersal distance is greater than that of males (Dunn and Braun 1985). Current genetic research in Alberta and Saskatchewan indicates some leks are genetically isolated from each other while others act as hubs for genetic flow from Montana (Bush pers. comm. 2006).
Females exhibit fidelity to nests (Fisher et al. 1993, Holloran and Anderson 2005) and winter sites (Berry and Eng 1985; Aldridge et al. 2004). Greater Sage-Grouse populations have been described as migratory or non-migratory (Eng and Schladweiler 1972; Wallestad 1975; Connelly et al. 1988). Migration can occur between winter/breeding and summer areas, winter and breeding/summer areas or by a combination of movements between winter, breeding and summer areas (Connelly et al. 2000a). Non-migratory grouse have been defined as those that do not make seasonal movements > 10 km (Connelly et al. 2000a). Greater Sage-Grouse in Alberta and Saskatchewan are described as non-migratory, although seasonal habitat movements > 10 km are common (Aldridge 1998; McAdam 2003). An important corridor between western Saskatchewan and Alberta appears to be linking Alberta to the remaining population in Saskatchewan and Montana, enabling gene flow (Bush pers. comm. 2006). Movement distances > 200 km were documented from Alberta to Montana (Bush pers. comm. 2006).
Diet
Greater Sage-Grouse have a near obligate relationship with sagebrush for food and cover year-round (see Habitat). Sagebrush constitutes > 47-60% of adult diet in summer and 100% in winter (Kerwin 1971; Wallestad et al. 1975). Greater Sage-Grouse lack a grinding gizzard but have adapted a long ceca and a soft food diet to aid digestion (Remington 1989).
Dietary requirements vary with age, reproductive stage, and season. Forbs make up the remainder of adult summer diet and may be important to reproductive success of pre-laying hens (Barnett and Crawford 1994; Gregg et al. 2006). Forbs are associated with invertebrate biomass in sagebrush (Jamison et al. 2002) and invertebrates are critical in the diet of chicks in their first weeks post-hatch (Klebenow and Gray 1968; Johnson and Boyce 1990; Drut et al. 1994). As chicks develop, there is a dietary shift to include forbs and succulent shrubs (Patterson 1952; Klebenow and Gray 1968; Klebenow 1969). In Saskatchewan, forbs were predominant in the summer diet of Greater Sage-Grouse broods (Kerwin 1971). Forbs have greater protein content than other vegetation types (Peterson 1970) and may influence chick growth rates (Huwer 2004) and survival (Johnson and Boyce 1990; Aldridge 2005; Dunbar et al. 2005). Sagebrush becomes increasingly important to chicks as they approach 3 months of age (Peterson 1970).
Adaptability
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 (Aldridge and Brigham 2002; Aldridge and Boyce 2007). Hot, dry years with low precipitation in spring and summer have been shown to increase the risk of nest and chick failure influencing annual population recruitment (Aldridge 2005). Heavy grazing may further impact herbaceous cover available for nesting and brood-rearing; livestock concentrate in areas of greater moisture during drought conditions (Braun 1998; Adams et al. 2004). Dry conditions, such as those seen in southeast Alberta from 1978-1995, adversely impact Greater Sage-Grouse habitat (McNeil and Sawyer 2003). Conversely, cool weather or heavy precipitation coinciding with hatch of chicks can negatively influence fall recruitment (Patterson 1952). Additionally, deep snow can severely reduce habitat quality in winter (Beck 1977; Hupp and Braun 1989).
Translocations to introduce, reestablish, or augment a population have met with limited success. Greater Sage-Grouse are difficult to raise in captivity and are poor candidates for release. Few chicks (5%, n = 148) captured by Johnson and Boyce (1990) survived to maturity; mortality was attributed primarily to disease. Breeding success for those that reached reproductive age was minimal (Johnson and Boyce 1990). Egg collection, storage and incubation techniques were effective in hatching 73% (n =112) of eggs in northwest Colorado for experimentation (Huwer 2004). However, meeting the nutritional needs of the human-imprinted chicks was difficult and most chicks succumbed from malnutrition (Huwer 2004). Successful attempts at husbandry have occurred at the Buttes Environmental Research Facility in Laramie, Wyoming (Spurrier et al. 1994) and at the United States Department of Agriculture’s National Wildlife Research Center in Fort Collins, Colorado (Oesterle et al. 2005). The 21 juvenile grouse kept at the latter facility experienced low mortality (17%) and breeding was attempted (Oesterle et al. 2005).
Restocking populations from captive-bred individuals has not been attempted, although it is known that wild individuals do not translocate well. Fifty-seven juvenile grouse from Oregon were released north of Richter Lake, British Columbia in 1958. Greater Sage-Grouse were seen near Osoyoos in the early 1960s but are now considered extirpated (Cannings et al.1987). In Saskatchewan in 1972 an attempt to reintroduce Govenlock grouse to the Saskatchewan Landing area failed. A lone bird was captured and it died upon release (Roy 1996). Translocations of more than 7,200 Greater Sage-Grouse range-wide have also met with little success (< 5%, n = 56), and authors suggest translocations be viewed only as an experimental strategy to restore extirpated populations (Reese and Connelly 1997).
It is not surprising that failure rates of translocations are high, given that habitat quality and quantity is already limiting existing (or extirpated) populations (Schroeder et al. 2006). Translocations should only be considered as a management strategy if the configuration, quality, and quantity of available habitat can support a viable population with minimal long-term management intervention (IUCN 1998).
Page details
- Date modified: