Recovery Strategy for the Grizzly Bear (Ursus arctos), Prairie Population, in Canada
- 1.1 Assessment information from COSEWIC
- 1.2 Species description
- 1.3 Populations and distribution
- 1.4 Needs of the Grizzly bear (Prairie population)
- 1.5 Threats
- 1.6 Suitable habitat
Date of assessment: May 2002
Common name: Grizzly bear (Prairie population)
Scientific name: Ursusarctos
Committee on the Status of Endangered Wildlife in Canada (COSEWIC) status: Extirpated
Reason for designation: Extirpated in the Prairie region of Canada.
Canadian occurrence: AB, SK, MB
COSEWIC status history: The species was considered a single unit and designated Not at Risk in April 1979. Split into two populations in April 1991 (Prairie population and Northwestern population). The Prairie population was designated Extirpated in April 1991. Status re-examined and confirmed in May 2000 and in May 2002. Last assessment based on an update status report.
The grizzly bear (Ursus arctos) is larger than the black bear (Ursus americanus). It has a distinctive hump between its shoulder blades that is not present in the black bear. The grizzly bear has a nose that turns up at the end, unlike that of the black bear whose nose arches down. Grizzlies are typically browner than black bears, although they can range from nearly white through blond to black. The guard hairs on the shoulders and back of grizzlies are often tipped with white, which gives the fur a grizzled appearance. Another distinctive characteristic of grizzly bears is their fossorial fore-claws used for digging out winter dens, roots, and rodents (Schwartz et al. 2003).
Grizzlies are sexually dimorphic: males are 1.8 times larger than females on average (Hilderbrand et al. 1999). Typical body mass of an adult female ranges from approximately 100-125 kg for interior populations to 225 kg for coastal bears in North America (Schwartz et al. 2003). Apart from a few anecdotal reports, there is little information on the physical characteristics of grizzly bears from the Prairie population, but their size was probably similar to bears living in the interior.
Ursos arctos is commonly known world-wide as either a grizzly or brown bear. Historically, its distribution included Asia, the Middle East, North Africa, Europe, Great Britain, and North America (Servheen 1990 in Kansas 2002). The global distribution and abundance of grizzlies decreased from the mid-1800s to present by an estimated 50% (Servheen 1990 in Ross 2002). Grizzly bear populations are known, or believed, to occur now within the holarctic regions of 42 Eurasian countries, the U.S.A., and Canada, but many of these populations are insular, small, and endangered (Servheen et al. 1999 in Ross 2002, Ross 2002, Proctor et al. 2005).
Grizzlies lived across North America prior to European settlement (Nielsen 1975, Banci 1991). A glacial fossil record of a grizzly bear, 11 700 ± 250 years old, was found in southern Ontario (Peterson 1965 in Ross 2002). Historically, grizzlies occurred in northern and western North America (Figure 1), although some patches were vacant (Mattson and Merrill 2002), and some small outlier populations (e.g., Labrador) apparently existed (Loring and Spiess 2007).
The decline of grizzly bear populations during the 19th century was mainly attributed to European exploration and settlement, and the associated introduction of firearms (Banci 1991, Mattson and Merrill 2002, Ross 2002). The population decline on the Prairies was especially severe, aggravated by the eradication of wild bison (Bison bison) and the advent of agriculture (Nielsen 1975, Mattson and Merrill 2002, Alberta Grizzly Bear Recovery Team 2005). Grizzly bears were rarely seen on the Canadian Prairies after 1900 (Nielsen 1975, Kansas 2002).
Adapted from Mattson et al. 1995, McLellan 1998, Kansas 2002, Ross 2002, and Hamilton et al. 2004; prepared by Environment Canada 2008).
Description of figure 1
Figure 1 provides a visual representation of the historical and current range of the Grizzly Bear in North America.
COSEWIC identified two separate populations of grizzly bears: i) the Northwestern population (NWP), designated as Special Concern, and ii) the Prairie population, designated as Extirpated. The NWP is within Canada's current grizzly bear range (Figure 1), exclusive of the Prairie Ecozone (Figure 2). The Prairie population represents grizzly bears that occupied the Prairie Ecozone up to the 1880s. When conducting an assessment, COSEWIC occasionally distinguishes among groups or populations, if a single-status designation for a species will not accurately assess its extinction probability.
In 2002, approximately 27 000 - 29 000 grizzly bears comprised the NWP: greater than 14 000 bears lived in British Columbia; 6 000-7 000 bears in the Yukon, 5 100 in the Northwest Territories, 1 000 in Alberta, and 800 - 2 000 in Nunavut. Even though the Prairie population is extirpated, individual grizzly bears from the NWP still occasionally foray to the Alberta Prairie (Kansas 2002, Ross 2002, Morton and Lester 2004).
One of the earliest written accounts of an encounter with a grizzly bear on the Prairies was by Henry Kelsey in 1691 (Kelsey 1929). Written records from early explorers, fur-traders, naturalists, settlers, hunters, and the Geological Survey of Canada, are the primary sources used to describe historical wildlife populations. Our limited knowledge of the extirpated Prairie population of grizzly bears is based largely on these incidental observations, which may not accurately describe the population. For example, most historical observations occurred near a major river (Figure 3). This may be because humans often travelled and settled by water, and/or because bear densities were higher there.
During 1754, Henday reported grizzlies east of the Red Deer River, and around the Battle River Valley, near Wainwright (MacGregor 1954 in Nielsen 1975). During 1787, Thompson recorded numerous grizzlies in the Bow River Valley, as far east as Calgary. Bears were also present near Fort Saskatchewan (Nielsen 1975). Dr. J. Richardson, a naturalist, stated that grizzly bears were most numerous in the woody country along the eastern base of the Rockies, particularly in areas interspersed with open Prairies and grassy hills (Richardson 1829 in Nielsen 1975).
461 508 km2; Adapted from the Ecological Stratification Working Group 1995; prepared by Environment Canada 2008.
Description of figure 2
Figure 2 provides a visual representation of the Prairie Ecozone, which area was occupied by Grizzly Bears, Prairie population, up to the 1880s. The Prairie Ecozone size is approximately 461 508 km2 and it includes the Prairie region of Alberta, Saskatchewan and Manitoba.
The Palliser Expedition, 1857-1859, frequently encountered grizzlies along the South Saskatchewan, Bow, and Red Deer Rivers. Over two days, members saw seven grizzly bears in the river valley near Medicine Hat. Grizzly bears were also seen on the Prairies north of the Red Deer River (Nielsen 1975). Fur-trading records provide some indication of bear abundance. In 1871, Cowie, a Hudson's Bay fur-trader, received 750 grizzly skins while trading at the Cypress Hills; he estimated that independent traders obtained many more (Nielsen 1975).
By the late 1800s, grizzly bears were rarely seen east of the foothills. For example, Cowie first visited the Cypress Hills in 1871. When he returned twelve years later, he reported that the hills were empty of grizzly bear, elk, and bison (Stegner 1962 in Nielsen 1975).
The grizzly bear population in southern Alberta declined during the 19th century because of extensive hunting and mortality associated with human settlement, ranching, and farming, which increased after the Dominion Lands Act (1872) and the Canadian Pacific Railroad (1883) were established (Nielsen 1975).
Grizzly bears seemed common in Saskatchewan, especially near major rivers (e.g., Battle, North Saskatchewan). During the 1850s, it was well known that grizzlies occurred far down the South Saskatchewan River (Hind 1860 in Nielsen 1975). Grizzly bears were frequently seen near Devil's Lake and Fort Pitt near Lloydminster (Graham 1847 in Nielsen 1975). A "considerable number" of grizzly bear skins were brought to Fort Pelly in 1857; more were traded when the carts from Fort Qu'Appelle, Fort Ellis, and the Touchwood Hills arrived (Klaus 1961 in White 1965). Grizzlies were also observed outside of the Prairie Ecozone, east and north of Prince Albert: Birch Hills in 1772, Nipawin in 1808, Prince Albert in 1820, Pasquia Hills and Cumberland House in 1784, and Wapaweeka Hills near La Ronge (White 1965, Nielsen 1975). During the 1920s, a few grizzlies were reportedly present in the Pasquia Hills, which span the Manitoba-Saskatchewan border (Sutton 1967).
In southern Manitoba, grizzlies were not numerous in the Red River Valley, but were abundant in the Pembina Mountains. In his journals (1799-1814), Henry the Younger reported grizzly skins being obtained from the Pembina River Valley, Pembina Mountains, Portage La Prairie, and Salt River. In North Dakota, near the Manitoba border, grizzly bears were "very common" at Devil's Lake [Lac du Diable], and "seen in droves" on the banks of the Cheyenne [Schian] River, the "nursery of buffalo and deer" (Henry 1897 in Seton 1953).
Even though the Prairie population is extirpated, individual grizzlies from the Northwestern population sometimes travel from the Rocky Mountain foothills to the Prairies in Alberta. Since 1998, sightings of grizzly bears on the Prairies have increased, primarily in the St. Mary and Milk River drainages. These visits to the Prairies are usually short; however, occasionally, grizzly bears establish a semi-permanent residence (Morton and Lester 2004).
A draft Prairie Grizzly Operation Strategy was developed by the Alberta Government (Morton and Lester 2004). Their approach is to monitor the movements and behaviour of the few grizzly bears that frequent the Prairies and to respond to each unique bear accordingly. When possible, a grizzly bear is captured, tagged with a radio or satellite transmitter, and monitored. Information on habitat use by the bear and potential conflict areas is obtained, and can aid in alleviating fears and misconceptions the public may have. Management actions range from monitoring to direct intervention, such as removing attractants or relocating bears (Morton and Lester 2004).
Copied from Nielsen 1975; prepared by Environment Canada 2008.
Description of figure 3
Figure 3 provides visual representation of a list of the recorded observations of grizzly bears in Alberta and Saskatchewan during 1820-1869, including the name of the observer, the date, the location and the details associated with each observation.
Because there is scant information about the ecology of bears on the Canadian Prairies, much of what is presented in this recovery strategy is based on recent studies of interior populations of grizzlies in North America (see Ross 2002).
The biological needs of a grizzly bear vary distinctly by season. During winter, a grizzly resides in its den for 4.5-7 months, does not eat, catabolizes fat and proteins for sustenance (Ross 2002), and loses 16-37% of its body mass (Hellgren 1998in Ross 2002). Litters are born and nursed while mothers are dormant. Spring to fall, foraging is the primary activity, so the bear can replenish its depleted energy reserves and store fat for the next winter hibernation.
Grizzly bears have low reproductive rates because of late maturation, small litters, and long intervals between successive litters (Kansas 2002). On average, a mother has her first successful litter at 5-8 years of age. Litter size, based on surviving cubs, is usually 2, and rarely 4 or more. Litters are produced about every 3 years (Ross 2002, Garshelis et al. 2005, Schwartz et al. 2006). Female reproductive senescence occurs about age 28 (Schwartz et al. 2003).
An offspring accompanies its mother for 2-5 years (Garshelis et al. 2005, Schwartz et al. 2003). At independence, a young bear establishes its own home range. Sons usually disperse away, but daughters often establish home ranges next to or overlapping their mother's home range. Natal dispersal lasts 1-4 years (McLellan and Hovey 2001b in Ross 2002). In southeastern B.C., males dispersed 29.9 km and females 9.8 km, on average (McLellan and Hovey 2001b in Ross 2002). In Yellowstone National Park, the mean dispersal distance of 4 subadult males was 70 km (Blanchard and White 1991 in Ross 2002). Grizzly bears will occasionally disperse much further (e.g., 340 km; P.I. Ross unpubl. data in Ross 2002).
Grizzly bear longevity is highly variable and depends on several factors such as individual traits, population characteristics, habitat quality, and the level of protection from humans. During a long-term study in Alberta, the average age of grizzly bears handled was 15-18 years (G. Stenhouse pers. com.). The predicted average longevity was 13.6 years for females experiencing good conditions for survival, whereas it was 2.6 years for males exposed to less favourable conditions (Johnson et al. 2004). Grizzly bears can live >30 years (Schwartz et al. 2006).
Grizzly bears are opportunistic omnivores (Schwartz et al. 2003). The relative content of meat versus plant material in their diet depends on food availability, which varies by season and region (Ross 2002). Female body size and productivity (litter size) varies positively with the proportion of meat (e.g., Pacific salmon, Oncorhynchus spp.) in the diet (Hilderbrand et al. 1999). High berry consumption and meat are important for weight gain prior to hibernation (Ross 2002).
Diets of North American grizzly bears have been studied extensively (see Ross (2002) for an overview of studies in Canada). Roots (e.g., members of the sweetvetch genus,Hedysarum spp.), forbs, graminoids, horsetails (Equisetum spp.), sedges (Carex spp.), and berries (e.g., buffaloberry, Sheperdia canadensis; cranberry, Vaccinium spp.) are the main plant foods consumed. Ungulates, burrowed mammals, and carrion are the usual sources of meat in the diets of non-coastal bears (Ross 2002). Grizzlies will scavenge from other carnivores, such as cougars (Puma concolor) (Murphy et al. 1998).
There are few details about the diet of the Prairie population, but it was probably similar to the diet described above. Historical accounts tell of Prairie grizzlies consuming wild bison (Nielsen 1975, Mattson and Merril 2002), buffaloberries (Spry 1968), and chokecherries, Prunus spp. (Coues 1897 in Nielsen 1975). Today, Prairie sources of wild meat for grizzly bear consumption would be much reduced; the extensive herds of wild bison are gone and other sources of carrion would be much less because large carnivores rarely occur on the Prairies now.
Grizzly bears require "food, seasonal foraging habitat, denning habitat, and security in an area of sufficient size for survival" (U.S. Fish and Wildlife Service 2007).
Little is known of the specific habitat requirements of the Prairie population, other than from incidental historical observations (Figure 3; Spry 1968, Nielsen 1975). River valleys probably provided suitable forage for bears (M. Gibeau, pers. com.) because of the abundance of berries, roots, ungulates (Nielsen 1975), and carcasses of drowned bison (Nelson 1973 in Nielsen 1975). Relative to the exposed Prairie flats, valleys as well as ravines, coulees, and other depressions would have been more productive ecosites supporting more abundant plant growth and higher ungulate densities. In 1859, at Bad Hill, Saskatchewan (Figure 3), favourite habitat of the grizzly bear was described as the "many deep ravines, for the most part overgrown with poplars and thick brushwood"; two people gathering berries were attacked there by a grizzly bear concealed by bushes (Southesk 1969 in Nielson 1975).
Similarly, during the 1800s, in the western contiguous United States (U.S.), especially in the drier ecoregions, grizzlies seemed to concentrate along rivers and streams where food (including bison carcasses) and cover were more abundant (Mattson and Merrill 2002).
In the barren grounds of Canada's central Arctic, which has no tree cover like the Prairies, grizzly bears preferred eskers and tall shrub riparian zones (McLoughlin et al. 2002).
Steeper terrain in river valleys should provide better denning habitat, with more abundant snow insulation, relative to the open Prairie. In Alberta's Rocky Mountains, grizzlies prefer to den in habitats that support deep snow conditions. Typical site characteristics include: steep slopes (i.e., 30-80%), with north and east aspects (Kansas 2002). Among North American populations, grizzly bears consistently selected steep den sites (Linnell et al. 2000 in Schwartz et al. 2003).
Security at den sites appears to be an important factor. Grizzlies may respond to human disturbance around den sites by abandoning their dens, and/or increased activity and heart rates. Bears are especially sensitive around the time of den entry, and possibly during spring, when females with cubs are confined to the den area (Linnell et al. 2000 in Schwartz et al. 2003).
The goal of secure habitat is to minimize the mortality risk (see Section 1.5.1) and disruption to grizzly bears caused by human activities; the proximity or density of motorized access usually determines whether the habitat is considered secure (e.g., Gibeau et al. 2001, U.S Fish and Wildlife Service 2007) or suitable (e.g., Ross 2002, AGBRT 2005) for grizzly bears. Secure habitat, primarily national parks, wilderness areas, and large blocks of public lands, was considered essential to the recovery of the Yellowstone grizzly bear population (U.S Fish and Wildlife Service 1993; 2007).
The extent of a grizzly bear's home range can overlap with other grizzlies, and changes in response to social factors [e.g., sex, reproductive status, and density], and environmental factors [e.g., habitat quality and seasonal weather] (U.S. Fish and Wildlife Service 2007). Local climate influences the home-range area by affecting primary productivity and food availability (McLoughlin and Ferguson 2000 in Ross 2002). For example, home ranges are usually small in temperate coastal areas, where growing seasons are long and productive, and large in the dry and cold interior and northern regions. In Canada, the average size of an adult female home range was 52 km2 in the Khutzeymateen Valley, B.C., compared to 2434 km2 in the Central Arctic (Ross 2002). Also, within a region, the home-range size varies between 113 - 668 km2 in Canada's boreal plains (Ross 2002) and 35 - 884 km2 in the Central Canadian Rockies (Gibeau et al. 2001), for adult female grizzlies. Bears with access to dependable, high-quality food resources, typically have smaller home ranges than bears with unreliable and scattered foods (Schwartz et al. 2003).
The average home-range size of Prairie grizzlies is unknown, but was likely related to the abundance, distribution, and predictability of food resources. Productivity on the Prairies can vary substantially by year (e.g., drought conditions) and location, so it seems probable that Prairie grizzlies had relatively large home ranges, with core activity areas centred on productive ecosites, such as river valleys and coulees.
Population gGrowth: Survival and reproduction
Adult female survivorship often accounts for most variation in the population growth (λ) of long-lived iteroparous species (Crooks et al. 1998, Crone 2001). This appears true for grizzly bears (Harris et al. 2006). Even though extremely low reproductive rates were evident in Alberta's central Rockies, positive population growth (λ>1) was still possible because of high adult female survival (Garshelis et al. 2005).
Although female survival is most important, reproductive success also influences population growth. A female grizzly's reproductive performance is associated with her diet. A female's age of first reproduction varied primarily with vegetation productivity among interior North American populations of grizzly bears (Ferguson and McLoughlin 2000 in Garshelis et al. 2005). Litter size and female body mass correlated positively with the proportion of meat in the diet (Hilderbrand et al. 1999). Low productivity of adult females in Alberta was attributed to diet, possibly due to restricted habitat use because of human disturbance (Gibeau et al. 2001, Garshelis et al. 2005). The effects of habitat quality and diet on adult female survival and reproductive performance are important considerations when assessing the potential for the recovery of a grizzly bear population.
Population Recolonization: Dispersal
Grizzlies disperse short distances relative to other large carnivores (Ross 2002; see Section 1.4.1). Female offspring tend to reside near their maternal home range; this trait reduces the rate at which grizzlies can recolonize areas where breeding populations have been depleted (Weaver et al. 1996 in Kansas 2002). Grizzly bear dispersal is a slow process lasting 1-4 years (McLellan and Hovey 2001b in Ross 2002). During dispersal, offspring need habitat suitable for foraging and denning (Ross 2002), and a landscape not dominated by humans, so the potential for human-caused mortality is low (Proctor et al. 2005). The dispersal behaviour (i.e., short distance and long duration) and habitat requirements of grizzly bears, do not favour successful recolonization (i.e., re-establishing a viable population after extirpation) through natural processes, especially in human-dominated landscapes.
Grizzly bear populations in southwestern Canada are prone to being small and isolated, because the landscape is extensively modified, fragmented, and inhabited by humans. Genetic analyses revealed demographically-isolated, vulnerably small (≤ 100 animals) populations of grizzly bears in southern B.C.: inter-population movement was limited for females, and reduced for males, by a highway and associated settlements (Proctor et al. 2005). The authors attributed limited inter-population movement across the transportation and settlement corridor to bears avoiding human-activity centres, and increased bear mortality in these areas, due to bear attractants (e.g., garbage) and concerns about human safety (Proctor et al. 2005). A fragmented system will impede the persistence or recovery of a grizzly bear population, because small isolated populations are more likely to become extinct or extirpated (Lande 1988).
Human-caused mortality is the foremost threat to the persistence of grizzly bear populations in North America (Mattson and Merrill 2002, Ross 2002, AGBRT 2005, Schwartz et al. 2006, U.S. Fish and Wildlife Service 2007). Lesser yet pervasive threats are habitat loss and degradation, which adversely affect the vital rates and dynamics of grizzly bear populations (see Table 1).
|Threat Category||General Threat||Specific Threat*||Stress|
*Assumes no sport hunting permitted
Table 1 provides a visual representation of the Threat Classification Table for the grizzly bear, Prairie population . The threat categories identified in the table are: 1)human-caused mortality (see section 1.5.1), 2) habitat loss (see section 1.5.2), 3)habitat degradation (see section 1.5.3). Additional information included in the table briefly describes for each threat category the following: general threat, specific threat and stress.
Grizzly bear mortality is highest where bears and humans interact (Johnson et al. 2004). During 1850 - 1970, grizzly bear populations in the contiguous U.S. were more likely to persist where human densities were low (Mattson and Merrill 2002). During 1983 - 2001, humans were the greatest cause of grizzly bear deaths in the Greater Yellowstone Ecosystem (GYE) (Schwartz et al. 2006). Human causes of bear mortality are sport hunting, preservation of life or property, management actions, illegal kills, vehicle/train collisions, incidental trapping, and problems during relocation or research captures (e.g., Ross 2002, Schwartz et al. 2003, AGBRT 2005, Garshelis et al. 2005, Gibeau 2005, Haroldson et al. 2006).
Motorized access increases opportunities for humans to observe and encounter grizzly bears. Roadways typically have high human use (e.g., >1 vehicle / day, Johnson et al. 2004) and are associated with high grizzly bear mortality (McLellan and Shackleton 1988, Stenhouse et al. 2003a in AGBRT 2005, Johnson et al. 2004). For example, outside of national parks in Alberta, 89% of 172 human-caused grizzly bear deaths occurred within 500 m of a road (Benn 1998 in AGBRT 2005). Secure habitat (i.e., > 500 m from a motorized access route) is considered essential for the recovery of grizzly bears in the GYE (U.S. Fish and Wildlife Service 2007).
Grizzly bears living near humans may become habituated to humans, and are more susceptible to management actions because of concerns about public safety and/or economic loss (e.g., livestock depredation). Habituated and "conflict" bears are more likely to die (Mattson et al. 1992, McLellan et al. 1999, Gunther et al. 2004, Haroldson et al. 2006).
The growth of a grizzly bear population is sensitive to the survival of its adult females (see Section 1.4.4), and so, even small changes in this mortality rate may lead to a population decline. Grizzly bear populations can sustain only very low mortality rates (Schwartz et al. 2003).
The Prairie landscape has undergone a dramatic transformation during the past century. Much of the land in the Prairie Ecozone has been converted from native Prairie to cropland and hayland. Of the historical range, an estimated 1-39% of the mixed-grass Prairie and 14% of the short-grass Prairie remains (Samson and Knopf 1994). Human occupation of the Prairies is now extensive (Figure 5); approximately 80% of the land is privately owned (Riley et al. 2007). The dominant land use is agriculture (Figure 4); however, resource, rural, and urban developments are also common. A grizzly bear's mortality risk is high on agricultural lands (Johnson et al. 2004) and private lands (Schwartz et al. 2006), because of permanent human presence (U.S. Fish and Wildlife Service 1993). The six U.S. recovery zones for grizzly bears are comprised of only 2-20% private land; the remainder is public land (U. S. Fish and Wildlife Service 2008). Of the publicly-owned land in the Prairie Ecozone, much of it occurs as relatively small parcels, likely insufficient for the recovery of a grizzly bear population. For the recovery of the Yellowstone population of grizzly bears, the Primary Conservation Area measured 9 210 mi2 (23 854 km2, 2 385 400 ha; U.S. Fish and Wildlife Service 2007).
River valleys, considered important habitats for Prairie grizzlies (see Section 1.4.3), are not common in the Prairie Ecozone. During the past century, major Prairie rivers were dammed (e.g., South Saskatchewan, Qu'Appelle, Old Man), resulting in the permanent loss of habitats located on the floor and lower slopes of these river valleys, further reducing an already limited resource necessary for any recovery efforts.
Prepared by Environment Canada 2008. Source for vegetation cover: PFRA Western Grain Transportation Payment Program classified imagery (1993-2001).
Description of Figure 4
Figure 4 provides a visual representation of the natural vegetation cover in the Prairie Ecozone (Alberta, Saskatchewan, Manitoba). On the right side of the figure which is delimiting the Prairie ecozone, there is a colour coded legend for each of the following cover: in pale yellow: cropland; in brown: hayland; in white: grassland; in pale green: shrubs; in dark green: trees; in pink: wetlands; in blue: water bodies; in red: other lands.
Human infrastructure (e.g., towns, roadways, industrial facilities, utility right-of-ways) degrades habitat for grizzlies (Ross 2002, AGBRT 2005). Genetic analyses reveal that grizzly bear populations in southwestern Canada are demographically fragmented: a highway and associated settlements limit female and reduce male movements among populations (Proctor et al. 2005). Near human developments and activities, female grizzlies underutilized productive habitat (Mattson et al. 1987, McLellan and Shackleton 1988, Mace et al. 1996, Gibeau and Stevens 2005). In contrast, in areas with little human disturbance, grizzly bears use high quality habitats efficiently (Gibeau and Stevens 2005). Adverse effects on bear foraging behaviour can translate into reduced body mass and reproductive output, and increased mortality.
Also, in developed areas, improperly stored human garbage and food may attract a bear, which will usually result in a management action. Bears with a history of management actions or conflicts with humans are less likely to survive (Johnson et al. 2004, Haroldson et al. 2006). Motorized transport (e.g., vehicles, trains) can disturb bears, and increase the likelihood of a bear being injured or killed (e.g., Mattson et al. 1987, Nagy et al. 1989, Gibeau et al. 1996). A characteristic of the Prairie landscape is the grid road system which provides extensive motorized access (i.e., north-south roads at one-mile intervals and east-west roads at two-mile intervals), which would not favour grizzly bear survival.
Lastly, climate change may affect vegetation productivity on the Prairies, in a region that already experiences extreme conditions, such as droughts. A bear's growth and reproduction would likely decrease, and its home range increase, if food was less nutritious and abundant.
Suitable habitat is determined by the grizzly bear's ecological requirements, at the individual and population level (see Section 1.4), in combination with reducing threats to the species (see Section 1.5). Habitat selection by grizzly bears is variable, and depends on factors such as individual characteristics (e.g., age, sex, reproductive status), seasonal and yearly weather, abundance and distribution of food, competition, and other biotic and abiotic factors (McLoughlin et al. 2002). To account for detailed habitat requirements of grizzlies on the Prairies would require specific data on habitat use and food resources which is not available for the extirpated Prairie population. No populations of grizzly bears currently exist in Prairie habitat exclusively, so extrapolations of a general nature were made from interior North American populations, mainly located in mountains and foothills. Food resources are not accounted for and are recognized as an important gap in the habitat assessment.
To predict whether there is sufficient suitable habitat presently available to recover the Prairie population of grizzly bears, we developed a spatially-explicit habitat model based on coarse-scale geographical data, and a set of simple but important criteria obtained from peer-reviewed journals, expert opinion, and historical observations. An essential feature of this predictive model is that each adult female would have a small area of secure habitat (sensu stricto Gibeau et al. 2001) within her life range. The secure habitat would provide some denning and foraging opportunities, and reduce the potential for human disturbance and human persecution. Food abundance, however, was not modeled.
Geographical information system techniques, described in the appendix, were used to predict potentially suitable habitat in the Prairie Ecozone for adult female grizzly bears, consisting of a 900 km2 life range centered on ≥ 9 km2 of secure habitat for each adult female.
Secure habitat: Model criteria
Habitat was identified as secure if the following criteria all applied:
- ≥ 9 km2 area
- > 500 m from a roadway or railway
- < 0.5 humans / km2 (Figure 5)
- area covered by natural vegetation (cultivated land considered not secure; Figure 4)
- area consists of drainage landforms: u-shaped valley, canyon, deeply incised stream, midslope drainage, shallow valley, upland drainage; headwaters
- area intersects with a lake or watercourse
In the central Canadian Rockies, suitable grizzly bear habitat was considered secure (less potential for bear-human interactions), if it was ≥ 9 km2 (based on the average 1.7 km daily foraging radius of an adult female), and if it occurred > 500 m from a feature with high human use (> 100 human visits / month), (Gibeau et al. 2001).
When restoring grizzly bear populations, Mattson and Merrill (2002) recommended including core areas with < 0.5 humans / km2, because grizzly bear mortality is positively correlated with human presence (see Section 1.5; Figure 5).
Grizzlies on the Prairies would require some natural (non-cultivated) vegetative cover for foraging (M. Gibeau pers. com.), resting and cooling (AGBRT 2005), and as security from humans. In vegetated areas, grizzlies are less visible, so less likely to be killed by humans (AGBRT 2005). The frequency of bear-human interactions is likely related to the complexity of local topography, as well as, the extent of vegetation cover (Mattson and Merrill 2002).
Statistics Canada 2006; prepared by Environment Canada 2008. Source for human density information: Statistics Canada 2006 Census Subdivisions.
Description of figure 5
Figure 5 provides a visual representation of the Human density, by census subdivision, based on Statistic Canada 2006 Census, for the Prairie Ecozone (Alberta , Saskatchewan, Manitoba). On the right side of the figure which is delimiting the Prairie Ecozone, there is a colour coded legend indicating the number of humans/km2 as follows: in gray: 0-0.55 humans/km2; in brown: 0.55-6.9 humans/km2; in pink:7-100 humans/km2; in red: more than 100 humans/km2.
Because a grizzly's active season is only 5-7 months, during which a bear must gain sufficient body mass to supply the energetic requirements of its next denning cycle, bears generally tend to concentrate seasonal activity in the most productive habitats available (Schwartz et al. 2003). On the Prairies, grizzlies should concentrate in river valleys where foraging opportunities are likely the most abundant (M. Gibeau pers. com.). Steeper terrain, present in river valleys and coulees, would also be suitable for bear dens and as secure cover. Historical records of Prairie grizzlies are often associated with river valleys (see Section 1.3.1). Assuming relatively high habitat use in river valleys was key to assessing secure grizzly bear habitat in the Prairie Ecozone, and is accounted for by including drainage and hydrological landforms in the predictive model.
Life-range habitat: Model criteria
Suitable life-range habitat was identified if the following criteria all applied:
- secure habitat is present (as identified above)
- ≥ 900 km2 area
- road density ≤ 0.6 km / km2
- < 0.5 humans / km2 (Figure 5)
- < 10 % cultivated land (cropland and hayland)
When examining the persistence of grizzly bear populations over multiple generations, researchers sometimes prefer a lifetime measure of habitat use, called a "life range", rather than an annual measure of home range. In their analysis of grizzly bear extirpation in the contiguous U.S., Mattson and Merrill (2002) chose a 900 km2 life range for adult female grizzly bears based on their knowledge of historical ecological conditions in the western states. Following Mattson and Merrill (2002), a life range of 900 km2 was chosen to predict the habitat requirements of an adult female grizzly bear on the Prairies, which is reasonable given the home range sizes observed for Canadian populations of grizzly bears (see Section 1.4.3; Table 5 Ross 2002).
High quality grizzly bear habitat should have open-road densities ≤ 0.6 km / km2, such that human-caused mortality of grizzly bears does not exceed a sustainable rate (AGBRT 2005).
When restoring grizzly bear populations, Mattson and Merrill (2002) recommended including extensive core areas with < 0.5 humans / km2. Low human densities would be especially important in a Prairie landscape where secure cover for grizzly bears is minimal.
Because agriculture in the Prairie Ecozone (Figure 4) is ubiquitous, most potential grizzly bear habitat would include some agricultural land, with an elevated mortality risk (Johnson et al. 2004). Grizzly bears in hayland and cropland (annually-seeded crops or summer fallow) would be highly visible to humans, especially after harvest. A potential life range with ≥10 % hayland and cropland was considered unsuitable habitat for a grizzly bear because of high mortality risk (K. Morton pers. com.). Grizzly bears should concentrate in the most productive habitats (i.e., river valleys), however, when productivity is low (e.g., few berries), bears would likely explore other food sources within their home range. Cattle grazing occurs on the remaining grasslands in the Prairie Ecozone, and varies in intensity by location and year. In the western U.S., grizzly bear range declined from 1920 to 1970 as cattle density increased (Mattson and Merrill 2002). Although not accounted for in this model, the mortality risk to Prairie grizzlies would likely increase with the intensity of cattle grazing.
Twenty-five (25) overlapping life ranges were identified as potentially suitable habitat for adult female grizzly bears in the Prairie Ecozone, located primarily in the areas of Cypress Hills, Milk River drainage, and Grasslands National Park (Figure 6). Accounting for roadways and railways reduced potentially secure habitat the most (Table 2). In contrast, cropland and hayland had the greatest negative effect on potentially suitable life-range habitat (Table 3). To support a population of grizzly bears, it is necessary to have large areas of continuous habitat suitable for their survival (see Sections 1.4.4 and 1.5). Our model predicts that the Cypress Hills and the Milk River drainage would have the largest area of continuous suitable habitat, sufficient for only 17 adult female grizzlies. The remaining eight (8) life ranges represent small, isolated habitat polygons, separated from the Cypress Hills-Milk River habitat polygon, by long (> 75 km) stretches of unsuitable habitat (Figure 6). It is important to note that this analysis did not take into account food resources and that the threat of human-caused mortality risk still exists; these are recognized as important gaps.
|Model features (see Section 1.6.1)||# Polygons ≥ 9 km2||Total polygon area (km2)||% Prairie ecozone|
|Drainage landforms only||270||14 389||3.12|
|Drainage landforms and human density||238||9 029||1.96|
|Drainage landforms and road/rail buffers||222||4 065||0.89|
|Drainage landforms and vegetation cover||291||8 731||1.89|
|Drainage landforms and hydrology||260||14 274||3.09|
|Secure habitat: meets all criteria||93||1 453||0.31|
Table 2 provides a visual representation of the resulting identification of secure habitat based on a spatially-explicit habitat model (see Section 1.6.2). This table includes, for each model feature and for the resulting secure habitat, the following: number of polygons ≥ 9 km2; total polygon area (km2) ; % Prairie Ecozone.
|Model features (see Section 1.6.1)||# Secure habitats ≥ 9 km2||Total secure area (km2)||Total life-range area (km2)||% Prairie ecozone|
|Life ranges with secure habitat that meet human and road/rail density criteria, but not agricultural criteria||67||1 068||31 324||0.23/6.8|
|Suitable life ranges: meets all criteria||25||534||11 710||0.12/2.5|
Table 3 provides a visual representation of the resulting identification of suitable life-range habitat based on a spatially-explicit habitat model (see Section 1.6.2). This table includes the following for a group of model features and for the resulting suitable life range: number of secure habitats( ≥ 9km2) ; total secure area (km2); total life-range area (km2); % Prairie ecozone (secure/life range).
Twenty five overlapping life ranges were identified as potentially suitable habitat for adult female grizzly bears in the Prairie Ecozone. Food resources were not accounted for and the threat of human-caused mortality of grizzly bears still exists in suitable habitats, especially on private lands, due to possible conflicts with humans and livestock (prepared by Environment Canada 2008).
Description of figure 6
Figure 6 provides a visual representation of a map of Alberta and Saskatchewan showing the resulting secure habitat and suitable life ranges for grizzly bears in the Prairie Ecozone based on the spatially-explicit habitat model used . The colour coded legend associated with this map and appearing at the bottom right corner of the figure indicates the following: delineation of the Prairie Ecozone in orange; delineation of secure habitat (≥ 9 km2) in pale green; delineation of suitable life range (900 km2) in brown. The map shows that the Cypress Hills and the Milk River drainage would have the largest area of continuous suitable habitat. The remaining eight (8) life ranges represent small, isolated habitat polygons, separated from the Cypress Hills-Milk River habitat polygon, by long (> 75 km) stretches of unsuitable habitat.
- Date Modified: