Recovery Strategy for the Greater Sage-Grouse (Centrocercus urophasianus urophasianus) in Canada
- 1.1 Species assessment information from COSEWIC
- 1.2 Description
- 1.3 Population and distribution
- 1.4 Needs of the greater sage-grouse
- 1.5 Threats
- 1.6 Actions already completed or underway
1.1 Species assessment information from the Committee on the Status of Endangered Wildlife in Canada (COSEWIC)
Common Name: Greater Sage-Grouse, urophasianus subspecies
Scientific Name: Centrocercus urophasianus urophasianus
Assessment Summary: This population, estimated to be between 550 – 800 individuals in 1997, is small and declining. Historic population levels and range are greatly reduced due to limiting factors including loss and fragmentation of sagebrush habitat on which the species depends, human disturbance, drought and harsh winter weather.
COSEWIC Status: Endangered
Reason for designation: Declining low population numbers; decreased occupied range.
Canadian Occurrence: Alberta and Saskatchewan
COSEWIC Status History: Listed as threatened in 1997. Listed as endangered in 1998. Confirmed as endangered in 2000. (COSEWIC, 2006)
Greater Sage-Grouse are the largest of the indigenous North American grouse in the Tetraonidae family and include two species; Centrocercus urophasianus urophasianus (Greater Sage-Grouse hereafter Sage-Grouse) and C. minimus (Gunnison’s Sage-Grouse) (see Canadian Sage-Grouse Recovery Team, 2001). This report deals with the C. u. urophasianus population that occupies habitat in southeastern Alberta and southwestern Saskatchewan at the northern fringe of North American Sage-Grouse range. In the U.S., C. urophasianus phaios was considered the western subspecies and C. urophasianus urophasianus the eastern subspecies, however using genetic and ecological data (Benedict et al. 2003), the Fish and Wildlife Service decided that the two Sage-Grouse subspecies would be considered one species (Centrocercus urophasianus) across its range. In Canada COSEWIC and SARA still list scientific name as Centrocercus urophasianus urophasianus and the common name as Greater Sage-Grouse, urophasianus subspecies.
The Sage-Grouse is a large, round-winged, ground-dwelling grouse that has finely marked brown, black, buff, and dull white upper parts. Both sexes have a black abdominal patch, which is larger on males. The long tail feathers are variegated and gradually taper to an acute point. Males have an arched yellow comb above the eye, a black throat, a large white patch on the breast and long feathers behind the head at the back of the neck (Connelly et al. 2004). Concealed within the white breast feathers of males are two large air sacs that are inflated and deflated during courtship displays. Male Sage-Grouse average 2.6 kg and measure an average of 65 – 75 cm in length. Females average 1.3 kg and measure 48-58 cm in length (Godfrey 1986, Nelson and Martin 1953, Sibley 2003). There is some indication that Sage-Grouse in Alberta (and perhaps Saskatchewan) are larger than their southern counterparts with an average breeding weight of 3.1 kg for males (Aldridge 2000), and lengths of 69-86 cm for males and 46-61 cm for females (Fisher and Acorn 1998).
1.2.1 Reproduction and productivity
Sage-Grouse are polygynous (one male mating with more than one female with the female selecting the male with which she mates) (Bergerud 1988a, Connelly et al. 2004) with males performing ritualistic displays (strutting) on communal leks to attract and mate with receptive females (Connelly et al. 2004). Males begin displaying at leks as soon as sites are clear of snow (mid-March in Alberta) and continue until late-May (Aldridge 2000). Strutting commences before sunrise each morning and continues until about a half hour after sunrise (Aldridge 2000, Jenni and Hartzler 1978). Males also display during the pre-sunset hours but Kerwin (1971) found that typically the evening display was less intense, of shorter duration, and attended by fewer birds. However, males may also display well into the night during a full moon. Males arrive on leks earlier and display longer as the breeding season progresses, especially if there are females present (Jenni and Hartzler 1978, Patterson 1952, Scott 1942). In Alberta, breeding normally occurs over a two-week period with peak female attendance in early April. Most yearling males attend leks about 2-3 weeks after peak female attendance and after the majority of breeding has occurred (Aldridge 2000, Emmons and Braun 1984, Eng 1963, Jenni and Hartzler 1978). Not all males display at leks as some yearling males may display infrequently or not at all. There may also be mobile groups of yearling males that display for females away from traditional lek sites (Dunn and Braun 1986).
Sage-Grouse nest in a shallow bowl on the ground lined with vegetation and feathers. Most female grouse nest as yearlings (Bergerud 1998b, Coggins 1998, Schroeder 1997) but not all hens nest (range 63% - 100%) (Connelly et al. 2004, Holloran et al. 2001). More adults (78-92%) than yearlings (55-79%) initiate nests (Connelly et al. 1993, Connelly et al. 2004) and renesting rates vary from <20% to >80% (Connelly et al. 1993, Connelly et al. 2004, Eng 1963, Patterson 1952, Schroeder 1997). In studies by Aldridge (2000) and Aldridge and Brigham (2001), Alberta Sage-Grouse hens exhibited high reproductive effort with all adult and yearling hens initiating a nest. Of those that had a failed first nesting attempt, 36% renested. Average clutch size was 7.8 eggs (range 4-11) with first nesting attempts averaging 8.2 eggs and renests averaging 5.6 eggs. This is at high end of range-wide averages but similar to the average of 8.25 eggs (8.49 first attempt and 7.23 for renests) found in Montana (Moynahan et al. in press [a]). The mean date of initiation of incubation in Alberta was May 10 and nearly all (92%) eggs laid were fertile. Incubation averaged 27 days with a mean hatch date of June 5 (first nests May 28, renests June 30). Nest success (first and renests) was 46.2%, although adults were more successful (50%) than yearlings (25%). Hen breeding success was 55% and both nest and hen breeding success were within the range anticipated in more southerly locations. During subsequent research, Aldridge (2005) found lower nest success (35.3%) and suggests that drier conditions during his second study led to lower reproductive success (see Limiting Factors).
Sage-Grouse chicks are precocial, leave the nest soon after hatching, and are capable of weak flight at 10 days and strong flight at five weeks (Schroeder et al. 1999). Generally, chick survival is low with brood size declining by as much as 68% during the summer (Schroeder et al. 1999). Chick survival to 50 days of 33-38% is necessary to maintain populations (Schroeder 1997) but chick survival in Alberta was only 18% (Aldridge 2000 and 2001, Aldridge and Brigham 2002). Aldridge (2000) states that the proportion of yearlings captured at leks (25%) is low compared to averages elsewhere (44-46%) (Beck and Braun 1978, Dalke et al. 1963, Wallestad 1975) and this indicates low annual recruitment into the Alberta population.
Sage-Grouse are characterized as having low annual productivity but high adult survival (Connelly et al. 1994, Connelly et al. 2004, Schroeder 1997, Zablan 2003). There has been little research that documents seasonal mortality (Connelly et al. 2004). Aldridge et al. (2001) estimated female annual survival in Alberta to be 57%. Aldridge et al. (2004b) estimated 73-88% overwinter survival for adult females and 43% for juveniles in Alberta.
1.3 Populations and distribution
Sage-Grouse distribution in North America is tightly linked to the distribution of sagebrush (Artemisia spp.) (Connelly et al. 2004). Historically, the continental Sage-Grouse range spanned 1 200 483 km2 in fourteen states and three provinces (British Columbia, Alberta and Saskatchewan) (Schroeder et al. 2004) (Figure 1). The current distribution has been reduced to half of the historical range (668 412 km2) occurring in eleven states and two provinces (Alberta and Saskatchewan) (see Canadian Sage-Grouse Recovery Team ). The remaining range has been severely reduced and fragmented (Schroeder et al. 2004). What was formerly considered the Northern Great Plains race, C. u. urophasianus, (Benedict et al. 2003) currently occurs in Alberta, Saskatchewan, Montana, North Dakota, South Dakota, Idaho, Wyoming, Colorado, Utah, and Nevada.
Within prairie Canada, Sage-Grouse once occupied about 100 000 km2, split between Alberta and Saskatchewan (Aldridge 2000, Aldridge and Brigham 2003) (Figure 1). The current Sage-Grouse range in Canada has been reduced to about 6% of the historic range (6000 km2) (Aldridge 2000, Aldridge and Brigham 2003) (Figure 1). For detailed descriptions see Canadian Sage-Grouse Recovery Team (2001). Sage-Grouse populations are defined as a group of birds associated with one or more active leks in the same geographic area separated from other leks by >20 km (Connelly et al. 2004). Using these criteria, there are at least two and possibly more separate populations within prairie Canada outside of GNP including the southwest Saskatchewan leks that are at least 20 km apart (S. McAdam, pers. comm., Saskatchewan Environment). One population occurring across southeastern Alberta, southwestern Saskatchewan and north-central Montana, is separated by approximately 60 km from a second population spanning south-central Saskatchewan (Grasslands National Park (GNP) and surrounding area) and northeastern Montana.
Figure 1. Current distribution of Sage Grouse in Canada and (inset) historic and current distribution of Sage-Grouse in North America
Schroeder et al. 2004. Geological Surveys, Forest and Rangeland Ecosystem Science (http://sagemap.wr.usgs.gov/FTP/images/fig1.12.jpg).
Description of Figure 1
Figure 1 consists of a main map and an inset map. The main map displays the current Sage Grouse distribution, the Agriculture Canada OneFour research station, the Grasslands National Park, the Federal Community Pastures - PFRA, and roads. The inset map displays current and historic distribution of Sage-grouse in North America.
1.3.1 Population status and trends
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) listed Sage-Grouse in Alberta and Saskatchewan as a threatened species in 1997 and in 1998 this listing was elevated to endangered. Provincially, the Sage-Grouse was listed in Saskatchewan as potentially threatened in 1984, threatened in 1987 (Weichel and Hjertaas, 1992) and endangered in 1999, and endangered in Alberta in 2000. In 2000, COSEWIC confirmed the listing as endangered and it was listed as such under the Species at Risk Act in 2003.
There is no universal method for a complete census of a Sage-Grouse population. Instead, lek counts of strutting males during spring courtship displays are used as an index for local population status and trends (Autenrieth et al. 1982, Beck and Braun 1980, Connelly et al. 2000, Connelly et al. 2003). Frequent lek counts were conducted in Alberta from 1968 through 1991 (Appendix B). Commencing in 1994, annual lek counts have been conducted at all known active and inactive lek sites in Alberta (Appendix B). Some of the earliest lek counts in Saskatchewan were conducted in 1970 and 1971 (Kerwin 1971) and Provincial Wildlife staff throughout the 1970s and 1980’s counted select leks, however most of those data were incomplete or inconsistent (Appendix C) (see Weichel and Hjertaas 1992, S. McAdam, pers. comm., Saskatchewan Environment). Range-wide counts in Saskatchewan were not conducted until 1987 and 1988 (Harris and Weidl 1988) when 170 potential lek sites were checked (Appendix C) and annual lek counts were initiated in 1994 with varying levels of intensity.
Lek count data show considerable fluctuation in numbers of males, lending support to the suggestion that Sage-Grouse populations exhibit 8-10 year cycles of abundance (Braun 1998, Aldridge 1998a, Aldridge and Brigham 2003). However, the trend for North American Sage-Grouse populations has been a 2% per year decline between 1965 and 2003 (Connelly et al. 2004) with Canadian populations decreasing at a faster rate (Appendices appendixA and appendixB). Alberta’s numbers dropped from a high of 613 males in 1968, to a low of 70 in 1994, with a 2006 count of 90 males. Similarly, the number of occupied leks in Alberta has dropped from a high of 21 in 1968, to a low of 8 in 1994, with a slight increase to 9 in 2005 (Appendix B). The number of males/active lek increased from 29.2 in 1968, to a high of 32.8 in 1981, to a low of 8.8 in 1994, and is currently at 10.6 males/lek. Alberta’s lek data from 1968 to 2005 show a decrease of 84% in total number of males at leks, a decrease of 57% in number of active leks, and a decrease of 64% in number of males per active lek.
Data for Saskatchewan show similar declines with a high of 934 males in 1988, to lows of around 60 in 1997, 2004, and 2005 with some intermittent fluctuations (Appendix C). The number of active leks has decreased from a high of 61 in 1988 to a low of 8 in 1999, increasing somewhat during the early 2000s but dropping to 8 leks again for 2004 and 2005 (Appendix C). The number of males/active lek dropped from a high of 15.3 in 1988 with historical highs of 26.6 in 1970 and 28.4 in 1971 (Kerwin 1971) to a low of 6.1 in 1997, with current numbers of 7.8 in 2005. Between 1988 and 2005 in Saskatchewan, the number of males at leks has decreased 93%, the number of active leks has decreased by 87% and the number of males/active lek has decreased by 49%.
Data on the number of males attending leks can be extrapolated to provide a crude estimate of total spring breeding populations (Aldridge 1998a, Aldridge and Brigham 2003, Connelly et al. 2004). The low population estimate assumes a sex ratio of 2 females:1 male attending leks. The high population estimate assumes the same 2:1 sex ratio but also assumes that only 90% of lek locations are known, and that only 75% of males attend leks. Based on these estimates, Alberta’s Sage-Grouse population was highest in 1968 (1839-2724 birds) (Appendix B), lowest in 1994 (210-311 birds) and is between 285-422 birds in 2005. Alberta’s population decreased 77-84% from 1968 to 2005. Saskatchewan’s population estimates ranged from 2802-4151 birds in 1988 (Appendix C), dropping to a low of 180-267 birds in 2004, and currently is estimated at 186-276 birds. The Sage-Grouse population in Saskatchewan has declined 90-96% from 1988 to 2005. Harris (1998) speculated that the pre-settlement population of Sage-Grouse in Saskatchewan may have been near 10 000 birds and using this estimate the decline to 2005 has exceeded 97%. The total Canadian population (AB and SK) has declined from somewhere between 3834-5680 birds in 1988 to a total of approximately 471-698 birds in 2005, a decrease of 82-92% in less than two decades, while the historical range of Sage-Grouse in prairie Canada has been reduced by 94 percent (Aldridge 2000).
1.3.2 Proportion of population in Canada
Although North American population estimates for Sage-Grouse are difficult to calculate, Braun (1998) estimated the 1998 population to be 142 000 birds. Connelly et al. (2004) estimated the population of males at 50 566 and if the 2:1 sex ratio were used, this would indicate that the minimum breeding population is just over 150 000 birds. Hence, Canada’s population makes up less than one percent of the population of Sage-Grouse remaining in North America.
1.4 Needs of the greater sage-grouse
1.4.1 Ecological and social role
Sage-Grouse are the largest of indigenous North American grouse species (Aldridge 1998a, Connelly et al. 2004, Nelson and Martin 1953, Sibley 2003) and are sagebrush obligates. They are year-round residents in the sagebrush-grasslands of the semi-arid mixed-grass prairie of southeastern Alberta and southwestern Saskatchewan where they are at the northern extremes of the Sage-Grouse range in North America (Aldridge 1998a, Braun 1998, Connelly et al. 2000, Connelly et al. 2004). Sage-Grouse feed primarily on sagebrush leaves, with dependency on forbs and insects at various times of the year.
The Sage-Grouse is a unique upland bird with very high public appeal. Land users are acutely aware of and protective of Sage-Grouse on their properties. The annual breeding display by males at traditional leks is a wildlife viewing attraction for ecotourists and photographers. Educational institutions incorporate lek surveys into upland bird natural science programs and the unique status of the Sage-Grouse makes it an excellent candidate for inclusion in any educational program regarding sagebrush-grassland prairie ecosystems. In Alberta however, a moratorium on visiting lek sites has been recommended because of the potential for disrupting the birds (D. Eslinger, pers. comm., Alberta Sustainable Resource Development).
The dramatic courtship displays by breeding males at leks was of cultural interest among First Nations who created dances and costumes to mimic male strutting behaviour (Autenrieth 1981). Sage-Grouse were considered a source of food both prior to and after European settlement, albeit low quality because of poor taste. Sage-Grouse were hunted in Saskatchewan in an unregulated fashion until 1938, after which the species received protection under the Wildlife Act (Canadian Sage-Grouse Recovery Team 2001). There is evidence of numerous closed seasons during the early 1900s in Saskatchewan and anecdotal evidence suggests that residents hunted Sage-Grouse for food during the 1930s depression period (McAdam 2003). The species was considered a game bird in Alberta and was hunted from 1967 through 1995. Hunting seasons were short with small bag limits. Demand was low and birds were hunted primarily as a trophy species (Canadian Sage-Grouse Recovery Team 2001).
1.4.2 Food habits
Sagebrush is important for food as well as cover (Braun et al. 1977, Connelly et al. 2000, Connelly et al. 2004, Patterson 1952), with leaves comprising virtually 100% of the Sage-Grouse winter diet (Connelly et al. 2004, Patterson 1952, Wallestad et al. 1975). Forbs and insects are dietary requirements at other times of the year (Drut et al. 1994a and 1994b, Wallestad et al. 1975) and may be critical for hen reproductive success (Barnett and Crawford 1994) as well as growth and survival of chicks (Johnson and Boyce 1990, Johnson and Boyce 1991, Huwer 2004). The availability of forbs to pre-laying hens can influence nest initiation, clutch size, and reproductive success (Barnett and Crawford 1994, Coggins 1998, Connelly et al. 2004).
Insects and forbs are essential in the diet of chicks (Connelly et al. 2004, Drut et al. 1994b, Fischer et al. 1996, Huwer 2004, Kerwin 1971, Klebenow and Gray 1968, Patterson 1952, Peterson 1970, Connelly et al. 2004), with insects comprising up to 60% of the diet of week-old chicks (Peterson 1970). Newly hatched chicks deprived of insects die within 10 days of hatching (Johnson and Boyce 1990). Chicks <21 days of age need 15 g of insects/chick/day for survival and development, while those >21 days of age need insects for optimal development (Johnson and Boyce 1991). Chicks begin to consume forbs at about two weeks of age (Klebenow and Gray 1994, Peterson 1970) and forbs comprise up to 80% of their diet during later summer months (Kerwin 1971). Sage-Grouse production is greater when >80% of the chick diet is comprised of insects and forbs (Drut et al. 1994b). Forbs are a rich source of protein and provide habitat that enhances the availability of insects (Huwer 2004). Adult Sage-Grouse consume sagebrush, forbs and insects (Rasmussen and Griner 1938, Wallestad et al. 1975) during summer with sagebrush comprising <60% of their diet during this period (Hanf et al. 1994, Wallestad et al. 1975). Although Thorpe (2002) notes that the majority of forbs used by Sage-Grouse during the summer (Kerwin 1971) are exotic species, indicative of heavily used range, it is unknown if these forbs are selected preferentially or if they are used as the only nutritional foods available in an altered environment.
1.4.3 Habitat requirements
Sage-Grouse have specific habitat requirements within the sagebrush-grassland complex for feeding and loafing sites, breeding areas, nesting cover, brood-rearing areas, and wintering grounds (Braun et al. 1977, Connelly et al. 2003). The majority of research on Sage-Grouse habitat comes from the range of big sagebrush (Artemisia tridentata) (Connelly et al. 2004), which is taller, more robust, and provides greater cover than the silver sagebrush (A. cana) found in prairie Canada (Aldridge 2001, Aldridge and Brigham 2002, Thorpe 2002, McAdam 2003). The descriptions below use information from both types of habitat.
Leks are open areas of sparse vegetation (<26% ground cover) (Connelly et al. 2004, Patterson 1952) located slightly lower than surrounding areas, often near standing water (Aldridge 2000) with widely spaced sagebrush (7% cover, <10 cm) (Peterson 1980). Leks range in size from 0.4 -16 ha (Dalke et al. 1963, Patterson 1952, Scott 1942) and are typically surrounded by taller (15-30 cm) sagebrush flats (Peterson 1980) used for feeding, roosting, and nesting (Clark and Dube 1984, Peterson 1970, Thorpe et al. 2005). Females may pre-select areas with good nesting habitat, with lek site selection by males resulting from the presence of females (Connelly et al. 2000). Degradation of sagebrush flats near leks is an important factor in lek abandonment (McAdam 2003, Thorpe et al. 2005).
Sage-Grouse nesting habitat is typically a broad area of sagebrush (>1 km2 in Alberta) with horizontal and vertical vegetative diversity (Aldridge 2000). Alberta hens select large patches containing a heterogeneous distribution of taller and denser sagebrush (Aldridge 2000, Aldridge and Brigham 2002, Aldridge 2005) and taller (>18 cm) but less dense grass cover than random (Aldridge 2000, Aldridge 2005, Aldridge and Brigham 2002). Herbaceous cover provides both scent and physical nest concealment (DeLong et al. 1995). Nesting habitat is usually located near leks with average lek-to-nest distance ranging from 1.1 to 6.2 km. Autenrieth (1981) found 85% of nests ≤6.4 km from leks and Wakkinen et al. (1992) found >90% of nests ≤3 km from leks. In Wyoming and Montana, Holloran (2005) and Moynahan et al. (in press [a]) found 64% and 60% of nests within 5 km of leks. In Alberta, average lek-to-nest distance is 4.7 km (0.42 – 15.4 km) with only 41% of nests located within 3.2 km of a lek (Aldridge 2000). The degree of fragmentation of prairie habitat is important to success of ground-nesting birds as nests in small patches (<100 ha) of cover are subject to higher nest depredation than those in large patches (>1000 ha) (Herkert et al. 2003).
During the first 2-3 weeks post-hatch, Sage-Grouse use brood-rearing areas near nest sites (<3 km) consisting of sagebrush habitat (Berry and Eng 1985, Connelly et al. 2000). These areas have less sagebrush cover (14% canopy), with a greater canopy (15%) of grasses and forbs (Autenrieth 1981, Kerwin 1971, Martin 1970, Sveum et al. 1998, Wallestad 1971) with a diversity of insects (Dunn and Braun 1986, Drut et al. 1994a), which are important criteria for brood habitat (Huwer 2004, Klebenow 1969, Sveum et al. 1998). As sagebrush habitat dries during June and July, hens with broods seek out mesic wet meadow sites that are also richer in forbs and insects, (Klebenow 1969, Patterson 1952) and select nearby areas with larger sagebrush for roosting and loafing (Dunn and Braun 1986). Availability of these mesic habitats may be a limiting factor in both Alberta and Saskatchewan (Aldridge 2000, Aldridge 2001, Aldridge and Brigham 2002) and the risk of chick death increases as the drought index increases (Aldridge 2005). Low availability of mesic forb habitat may result in hens and broods spending greater time using riskier habitats to meet daily nutritional requirements (Aldridge 2005). Males tend to move away from lek sites to separate summer habitat areas (up to 9 km) that provide high-density sagebrush cover (Hagen 1999). Hens and broods move into dense sagebrush in late summer and fall before moving to wintering grounds (Drut et al. 1994a, Patterson 1952, Wallestad 1971).
During the fall, Sage-Grouse congregate in sexually segregated flocks (Beck 1977, Eng and Schladweiler 1972, Connelly et al. 1988). Winter flocks normally consist of <50 birds (median = 10-16 birds for males, 15-20 birds for females) (Beck 1977). There has been little investigation into winter habitat used by Sage-Grouse in prairie Canada but in other areas, habitat used during winter is influenced by temperature, exposure to winds, and snow depth (Connelly et al. 2004). Sage-Grouse will burrow into snow to reduce exposure to inclement conditions (Beck 1977). Winter sites are commonly on west or south facing slopes (<5% slope) or drainages (Beck 1977, Crawford et al. 2004). Most winter sites consist of tall (25-80 cm), dense (>20% canopy) sagebrush (Crawford et al. 2004, Eng and Schladweiler 1972, Hagen 1999, Hanf et al. 1994, Wallestad 1975) with access to sagebrush above snow for food (Connelly et al. 2000, Crawford et al. 2004, Eng and Schladweiler 1972, Patterson 1952, Wallestad et al. 1975) and cover (Beck 1977). Females tend to use denser stands than males (Beck 1977). Connelly et al. (2000) recommend maintenance of sagebrush with a canopy of 10-30% and plant height that is 25-30 cm above the snow.
1.4.4 Limiting factors
Aldridge (2005) suggests that only 11% of the entire sagebrush habitat in southeastern Alberta can be classed as primary or secondary nesting habitat with reasonable expectations of nest success. Evidence suggests that the availability of secure habitat for nesting and the lack of adequate forb and insect rich mesic habitat for chick survival is limiting in prairie Canada (Aldridge 2000, Aldridge 2005, Aldridge and Brigham 2003). Only 5% of this range can be considered primary or secondary brood rearing habitat with reasonable expectations of brood survival (source habitat) (Aldridge 2005). Finally, Aldridge (2005) considers 63% of the nesting habitat and 75% of the brood rearing habitat chosen and used by Sage-Grouse in Alberta to be high risk habitat for nests and broods, respectively, acting as sink habitat for production (high occurrence but low fitness). Sage-Grouse either miscue in their selection of habitat types or are forced, through habitat availability, to nest and rear broods in sink habitat with resulting poor annual production and recruitment (Aldridge 2005). The availability of quality winter habitat and the related effect on annual recruitment and survival has not been evaluated in Canada.
Sage-Grouse require large blocks of interconnected sagebrush habitats (Connelly et al. 2004, Patterson 1952). Habitat alteration that reduces patch size and removes or degrades the quality of sagebrush generally has negative consequences for all sagebrush obligates (Braun et al. 2002). Historically, bison (Bison bison), pronghorn (Antilocapra americana) and elk (Cervus elaphus) inhabited southern prairie Canada (Hood and Gould 1992, Rangeland Conservation Service Ltd. 2004), and varying levels of disturbance by grazing and fire resulted in a landscape typified by patchiness (England and DeVos 1969, Bradley and Wallis 1996, Hood and Gould 1992). Major factors involved in the decline of Sage-Grouse populations are the loss, fragmentation, and degradation of habitat (Braun 1998). Humans have altered all of the sagebrush-grassland range in North America (Braun 1998, Connelly et al. 2004, Perdix Professionals 2005) and the potential to sustain populations in an altered landscape is dependant on remaining suitable habitats to continue to provide the seasonally required habitat components. It is important to recognize that declines in Sage-Grouse populations have likely been caused by a complex of factors (Braun 1998) that also include predation, disease, direct mortality factors, alteration of hydrological regimes and climatic factors.
1.5.1 Habitat loss
Cultivation of sagebrush-grassland range is one of the primary causes of habitat loss and fragmentation across the North American Sage-Grouse range (Dalke et al. 1963, Harris 1998, McAdam 2003, Patterson 1952, Wallestad and Pyrah 1974). More than 70% of sagebrush-dominated rangeland has been converted to agricultural crops (Braun 1998) with losses of 80% in Saskatchewan since the early 1900s (Harris 1998). Loss of sagebrush habitat near leks has resulted in abandonment of leks in both Saskatchewan and Alberta (Aldridge 1998b, Dube 1993, McAdam 2003). McAdam (2003) assessed habitat parameters around occupied and abandoned Sage-Grouse leks in Saskatchewan. Cultivation rates within 3.2 km of currently active leks were 5.4 ha/year from 1955 to 1971, and 24.3 ha/year from 1971 to 1996, while those rates at abandoned leks were 25.5 ha/year and 63.7 ha/year for the same time periods (McAdam 2003). On a finer temporal scale, Thorpe et al. (2005) suggested that cultivation may have contributed to loss of habitat and lek abandonment historically, but loss of habitat since 1981 has been insignificant. Cultivation since 1988 is not thought to be a causative factor in population declines and lek abandonment in Saskatchewan (McAdam 2003, Thorpe et al. 2005).
1.5.2 Habitat degradation
Livestock grazing is one of the major agricultural impacts on the Canadian prairie. There are 2.3 million cattle in Alberta Agriculture’s Southern Region and 50% of the farmland (2.6 million ha) in that region is comprised of native pasture (Alberta Agriculture, Food and Rural Development 2003, Statistics Canada 2001). This magnitude of use is certain to have some impact on the vegetation composition and structure of native grasslands (Perdix Professionals 2005). For example, stocking intensity can markedly affect the amount of residual vegetation that remains after grazing (Van Poollen and Lacey 1979). There is some indication that a conservative level of grazing may be beneficial to Sage-Grouse. Natural succession on ungrazed range will result in climax vegetation communities (Bird 1961) leading to homogeneous plant composition (Rangeland Conservation Services Ltd. 2004). Light grazing maintains greater plant diversity (Stohlgren et al. 1999), and could increase abundance of forbs necessary for chick survival (Thorpe and Godwin 2003). Heavy grazing leads to natural selection for low-growing, prostrate forms of vegetation (Milchunas and Lauenroth 1993), which provides lower quality nesting cover. Thorpe and Godwin (2003) found that moderate grazing results in higher dominance of shorter grasses allowing forbs to flourish but also results in less vertical structure as cover for Sage-Grouse (Thorpe and Godwin 2003). Heavy grazing can decrease both annual and perennial forbs in grasslands (Hayes and Holl 2003). Depending on intensity, grazing can result in changes in habitat structure and species composition of both upland and riparian areas, and degradation of riparian habitat (Autenrieth et al. 1982, Call and Maser 1985, Patterson 1952, Rasmussen and Griner 1938). Thorpe and Godwin (2003) studied differences between grazed and ungrazed areas in Grasslands National Park. They looked at vegetation components important for sage grouse habitat and found only modest differences. This lack of difference was attributed to the fact that either grazing was at moderate levels, or because the period of protection in GNP had been too short for vegetation changes to become apparent; they concluded that vegetation patches that varied between lightly and heavily impacted may be needed to provide the best sage grouse habitat (Thorpe and Godwin 2003).
Removal of vegetation affects habitat suitability by increasing exposure of Sage-Grouse to predators and weather extremes (Aldridge 1998b). Reduction of tall grass and mid-height shrub cover in nesting habitat can increase nest predation rates (Gregg et al. 1994, Seida 1998, Watters et al. 2002). Residual grass cover in the spring following grazing is necessary for concealment of nests from predators (Beck and Mitchell 2000). Livestock grazing in Sage-Grouse range may result in trampling of sagebrush seedlings and a subsequent decline in sagebrush health in areas where cattle congregate (Adams et al. 2004, Connelly et al. 2000, Owens and Norton 1992) as well as a reduction in herbaceous understory required for secure nesting sites (Dobkin 1995). Adams et al. (2004) propose that silver sagebrush decreases in response to moderate to heavy grazing intensity while Thorpe and Godwin (2003) suggest that silver sagebrush is an ‘increaser’ species in response to grazing. It may be that sagebrush is an increaser under light to moderate grazing (Thorpe and Godwin’s study area) but a decreaser under moderate to heavy grazing intensity.
Prior to fire suppression, periodic fires were important in shaping the prairie landscape (Adams et al. 2004, Hood and Gould 1992, Rangeland Conservation Service Ltd. 2004) however, there is little information on the effects of fire in sagebrush areas. A combination of unburned and burned areas is often essential in providing a diversity of conditions needed to meet the requirements of species inhabiting sagebrush communities (Wrobleski and Kauffman 2003). Fire suppression is thought to increase big sagebrush canopy cover rendering it unsuitable as brood-rearing habitat (Kaufman 1990, Winward 1991). Fire can be used to open up dense sagebrush stands so that understory vegetation can increase (Nelle et al. 2000). Silver sagebrush, on the other hand, reproduces by both seeds and sprouting (Thorpe 2002). Light spring burning may result in increased production of new shoots (Adams et al. 2004) as well as resprouting in senescent plants or in areas trampled by livestock (Connelly et al. 2000, Owens and Norton 1992). There is a need for greater knowledge of the relationship between fire and the sagebrush community.
1.5.3 Habitat fragmentation
Human alteration of the environment via construction and water impoundments causes physical loss of sagebrush habitat (Braun 1998) and the creation of anthropogenic edge causes many bird species including Sage-Grouse to avoid areas adjacent to edges (Herkert 1994, Herkert et al. 2003, Holloran 2005, Howerter 2003, Koper 2004, Pasitchniak-Arts and Messier 1995, Stephens 2003). Noise and activity caused by humans disrupts local breeding activities and Sage-Grouse tend to avoid these areas (Braun 1998). Fences and power lines across sagebrush habitat create additional travel corridors for mammalian predators and perch sites for avian predators, effectively fragmenting Sage-Grouse habitat (Aldridge 1998b, Braun 1998).
Road construction impacts Sage-Grouse population viability by physically removing and fragmenting potential habitat as well as creating travel corridors for mammalian predators (Aldridge 1998b, Braun 1998). Increased vehicle traffic and disturbance of leks by people can disrupt breeding activities and may result in lek abandonment (Aldridge 1998b, Braun 1998, Connelly et al. 2000, Herkert et al. 2003). Even low levels of vehicular traffic (≤12 vehicles/day) within 3 km of leks may reduce nest initiation rates by hens and increase distances that hens move from leks during nest selection (Lyon and Anderson 2003). The avoidance of habitat near roads reduces range availability and contributes to decreased survival (Braun et al. 2002, Holloran 2005).
Increases in petroleum industry activities in southern Alberta in the late 1970s to early 1980s, and again in the 1990s coincide with dramatic Sage-Grouse population declines (Braun et al. 2002), although the declining Sage-Grouse population cannot be attributed to any single factor (Braun 1998). More than 1500 wells have been drilled within the Sage-Grouse range of southeastern Alberta and approximately 30% are still active (Braun et al. 2002). Exploration and extraction involves construction and/or operation of drilling rigs, pump jacks, pump shacks, compressor stations, as well as construction of roadways, pipelines, and power lines to service these facilities (Aldridge 2000). Most of these activities result in either direct habitat alteration through removal of vegetative cover (Aldridge 1998b, Braun et al. 2002) or fragmentation and increased disturbance. Noise from nearby pump jacks disrupts breeding activity at leks (Aldridge 2005, Braun et al. 2002, Dube 1993, Holloran 2005) and leads to lek abandonment (Aldridge 2000, Holloran 2005). Hens with broods show strong avoidance of human dominated landscapes and the risk of brood failure increases substantially with each well site that is visible within 1 km of brood-rearing areas (Aldridge 2005). Impacts from oil and gas extraction activities are both short and long-term (Braun et al. 2002, Holloran 2005). In Alberta, disturbance by oil and gas extraction and construction near leks has resulted in abandonment of at least six leks (Aldridge 1998a, Braun et al. 2002, Dube 1993) and, although not the sole cause of Sage-Grouse declines, there is no question that these activities are a major contributor to the cumulative landscape effects that are suppressing populations.
Currently, there appears to be acceptable gene flow between birds in Alberta, northern Montana, and Saskatchewan (K. Bush, pers. comm., University of Alberta) but loss of habitat or avoidance of habitat linkages by Sage-Grouse due to anthropogenic impacts could result in effective fragmentation of populations and loss of genetic heterozygosity. Isolation of populations can result in inbreeding depression as exhibited in isolated populations of other lekking species such as Greater Prairie-Chickens (Westemeier et al. 1998). Associated effects of population isolation can include loss of genetic diversity, inbreeding, reproductive morphological deformities and, ultimately, population extirpation.
Golden Eagles (Aquila chrysaetos), Ferruginous Hawks (Buteo regalis), Red-tailed Hawks (B. jamaicensis), Swainson’s Hawks (B. swainsonii), Rough-legged Hawks (B. lagopus), Gyrfalcons (Falco rusticolus), Northern Goshawks (Accipiter gentilis), Great Horned Owls (Bubo virginianus), Common Ravens (Corvus corvax), coyotes (Canis latrans), bobcats (Felis rufus), weasels (Mustela spp.) and American badgers (Taxidea taxus) are known to prey on Sage-Grouse (Autenrieth 1981, Schroeder et al. 1999, Patterson 1952). Northern Harriers (Circus cyaneus) and rattlesnakes (Crotalus viridis) are known to prey on Sage-Grouse chicks (Huwer 2004, Schroeder et al. 1999) and there is some indication that harriers may also attempt predation on adult males on leks (Fletcher et al. 2003). Coyotes, badgers, American Crows (Corvus brachyrhynchos), raccoons (Procyon lotor), skunks, weasels, red foxes, common Ravens, and Black-billed Magpies (Pica pica), are known predators of Sage-Grouse nests (Autenrieth 1981, Schroeder et al. 1999, Patterson 1952). Normal predation in an unaltered environment is not considered a limiting factor for Sage-Grouse (Connelly et al. 2000). Changes in predator and prey guild composition and abundance brought about by habitat alteration and human intrusion has an increasingly important effect on Sage-Grouse productivity (Aldridge and Brigham 2003). The cumulative result of these impacts appears to be manifested in low Sage-Grouse chick survival and recruitment into the breeding population despite high reproductive effort (Aldridge 2000, Aldridge 2005, Connelly et al. 2004). High predation rates are usually a secondary symptom of habitat deficiencies in an altered and fragmented habitat that does not provide protection from predators and may increase predator foraging efficiency through amplified amounts of edge (Braun 1998, Connelly et al. 2000, Greenwood et al. 1995, Sargeant et al. 1993, Stephens 2003). For example, Sage-Grouse will avoid habitat within 600 m of power lines and risk from predators is increased within 1 km of power lines (Braun 1998).
There is some indication that the numbers of some predators (e.g., coyotes) have increased on the southern prairies (Hyslop 1998, Vriend and Gudmundson 1996), likely in response to low fur prices, declines in harvest for the fur trade, and changing intraguild dynamics with the loss of the prairie wolf (Canadian Sage-Grouse Recovery Team 2001, Pruss 1994). Raccoons have increased substantially in the Canadian prairies over the past 30 years (Lungle 1991). The Sage-Grouse range overlaps with the reintroduced swift fox (Vulpes velox), which is a historical predator of Sage-Grouse egg and chicks.
Farm and ranch yards also alter the natural environment and create microcosms suitable to support of a suite of predators (Connelly et al. 2004, Howerter 2003, Stephens 2003). Domestic dogs (Canis familiaris) and cats (Felis cattus) can be predators while wild species, such as red foxes (Vulpes vulpes), and skunks (Mephitis mephitis), readily adapt to and thrive in these altered environments (Connelly et al. 2004).
Declines in the populations of the primary prey species of predators may increase the impact of predation on Sage-Grouse. The abundance of small mammals as prey species for avian and mammalian predators is strongly influenced by the degree of grazing that occurs (Koper 2004, Skinner et al. 1995). Skinner et al. (1995) found that the greatest biomass of small mammals occurs on ungrazed grasslands, suggesting that grazing intensity plays a major role in determining the abundance of small mammals as a food source for avian and mammalian predators. Predation is also of major importance to hens with broods as the amount of forb and insect food decreases (Braun 1998). Poorer quality feeding areas may force birds to spend greater times fulfilling nutritional requirements, to feed in poorer quality and potentially riskier habitat, or to travel farther to obtain adequate food, resulting in greater risk of predation and greater energy expenditure (Gregg et al. 1993, Fischer et al. 1996, Pyle and Crawford 1996).
Sage-Grouse are host to a variety of parasites and disease-causing organisms (Connelly et al. 2004, Kerwin 1971) but these are not considered major mortality factors (Connelly et al. 2004, Patterson 1952). However, the recent discovery of West Nile virus (WNv) in Sage-Grouse populations may be cause for concern. Mortality from WNv was discovered in four populations of Sage-Grouse in 2003, (Alberta, Montana, Montana-Wyoming border, and Wyoming) (Moynahan in press [b], Naugle et al. 2004) with survival decreasing by 25% (Naugle et al. 2004, Walker et al. 2004). Late summer survival in the WNv areas of Montana and Wyoming was 20% compared to 76% outside of WNv-infected areas (Walker et al. 2004) and male and female lek attendance was substantially lower during the following spring (Walker et al. 2004). Although no WNv antibodies were found in 112 blood samples collected from live birds within the infected areas in 2003 (Naugle et al. 2004), subsequent sampling in Wyoming revealed that 10% of infected Sage-Grouse do survive WNv and develop antibodies (D. Naugle, pers. comm., University of Montana, Missoula). However, with very low Sage-Grouse survival rates, WNv could potentially be devastating for small, fragmented populations (Naugle et al. 2004).
1.5.6 Direct mortality factors
Hens and broods using cultivated crops (e.g. alfalfa fields) as foraging areas are subject to injury and mortality from farm equipment (Aldridge 2000, Patterson 1952). Increased traffic volumes on roads and trails can increase collisions with vehicles (Aldridge 2005). Physical structures in the sagebrush-grassland range can result in avoidance behaviour by Sage-Grouse (fragmentation effect) and increased predator foraging efficiency (predator perches). Sage-Grouse are also killed by flying into power lines and fences (Aldridge 2000, Patterson 1952) and structures, such as hydro line towers, or communication towers (Call and Maser 1985). The increasing focus on wind power as a source of electricity generation should be of concern (D. Eslinger, pers. comm. Alberta Sustainable Resource Development) especially if wind turbine towers are erected in or near Sage-Grouse habitat.
1.5.7 Alteration of natural hydrology
Water impoundments in xeric landscapes can affect the health of sagebrush communities and the availability of mesic meadows and the associated food sources necessary for chicks. Impediments to natural flow of waters reduce the frequency of flood events that are important for the maintenance of sagebrush habitat (McNeil and Sawyer 2001). In southeastern Alberta, the number of water impoundments has increased four-fold in the last 50 years (McNeil and Sawyer 2003). Watters et al. (2004) suggest that the number of dams within 3.2 km of leks in southern Saskatchewan has increased 20% in the last 50 years and the number of reservoirs (as a result of these dams) has more than doubled. Livestock use is often intensified near impoundments resulting in degradation of surrounding sagebrush habitat (Canadian Sage-Grouse Recovery Team 2001). Water impoundments >50 ha can result in loss of brood habitat, lek sites, and winter habitat (Braun 1998).
Climatic variation, when combined with other stressors, can compound the effects of other impacts. Anthropogenic threats are compounded by impacts of drought. Drought conditions may affect Sage-Grouse through reduced herbaceous cover at nests and decreased availability of forb vegetation and insects in wet meadows during spring and summer (Aldridge 1998b, Fischer et al. 1996, Hanf et al. 1994). The availability of forbs in upland sagebrush habitat fluctuates dramatically and rapidly in response to temperature and precipitation (Huwer 2004). McNeil and Sawyer (2003) suggest that the lack of significant precipitation events from 1978 to 1995 in southeastern Alberta compounded the effect of increased impediments to natural water flows and may have adversely impacted sagebrush habitat. Not only is vegetative growth reduced under drought conditions but also livestock grazing in wet meadow areas intensifies as these areas usually have better vegetation production than upland areas (Canadian Sage-Grouse Recovery Team 2001). There may be interspecific competition between wildlife species (pronghorn and Sage-Grouse) for food resources (sagebrush and/or forbs) during drought events. Drought can exacerbate the degradation of habitat by grazing livestock if stocking rates are not reduced dramatically during these periods (Braun 1998). Reduction in the quality of habitat and vegetative cover not only results in lower reproductive effort but the lack of adequate cover may also increase predation rates and brood mortality (Braun 1998). Birds that are already reproductively stressed by other footprints on the landscape may not be able to cope with the additional stressor associated with drought conditions.
Years with good winter moisture carryover or springs with average or above average moisture regimes may result in increased Sage-Grouse production (Autenrieth 1981, Wallestad 1975). However, heavy rainfall during egg laying or unseasonably cold temperatures with precipitation during the hatch period may result in nest failure or poor hatch rates (Wallestad 1975).
1.6 Actions already completed or underway
A number of initiatives have enhanced knowledge about Sage-Grouse in silver sagebrush communities of prairie Canada. Pertinent studies that have been completed or are in progress are:
- Ongoing annual spring surveys of strutting males at active and inactive leks in Alberta, Saskatchewan, and Grasslands National Park (pers. comm., S. McAdam, Saskatchewan Environment; D. Eslinger Alberta Sustainable Resource Development; P. Fargey, Parks Canada Agency).
- One spring aerial survey (2004) in search of new Sage-Grouse leks in southern Saskatchewan (pers. comm., S. McAdam).
- Aerial photographic interpretation/mapping of silver sagebrush communities in Alberta and Saskatchewan (Jones et al. 2005, Penniket and Associates Ltd. 2003, 2004).
- Relationships between silver sagebrush soils and landscapes associated with silver sagebrush and Sage-Grouse in Alberta with predictive mapping tools to assist in habitat management (McNeil and Sawyer 2001).
- Relationships between soil nutrients, grazing patterns and the presence or absence of active and inactive leks in southern Saskatchewan (King et al. 2005).
- The ecology of silver sagebrush and beneficial grazing management practices for Sage-Grouse in southeastern Alberta (Adams et al. 2004).
- Assessment of sagebrush range health and water impediments around Sage-Grouse leks in southern Saskatchewan with site plans for areas surrounding leks in the Frenchman Valley watershed, Saskatchewan (Watters et al. 2004).
- Effects of water impediments and precipitation on sagebrush habitat in southeastern Alberta (McNeil and Sawyer 2003).
- Habitat vegetative characteristics and land use patterns around active and inactive leks in southern Saskatchewan (McAdam 2003, Thorpe et al. 2005).
- Vegetative differences between grazed and ungrazed sagebrush lands in Grasslands National Park (Thorpe and Godwin 2003).
- Habitat use, habitat characteristics, and reproductive parameters of Sage-Grouse in southeastern Alberta (Aldridge 2002, 2005).
- Ongoing research (Ph.D. study – K. Bush, in progress) into level of historic and current genetic diversity and genetic isolation in Sage-Grouse populations in Alberta, Saskatchewan, and Montana.
- Established study sites to monitor relationship between livestock use and habitat characteristics pertinent to Sage-Grouse (D. Eslinger, pers. comm., Alberta Sustainable Resource Development).
- Completion of a provincial Sage-Grouse recovery plan for Alberta outlining objectives and strategies to be pursued to achieve population recovery (Alberta Sage-Grouse Recovery Action Group 2005)
- Completion of conservation plans by a multi-jurisdictional northern mixed-grass trans-boundary initiative for several ecosystem landscapes in southern Alberta, southern Saskatchewan, and northern Montana with Sage-Grouse as one of the target species of special significance (Smith Fargey 2004).
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