Effects of Winter Recreation on Grizzly Bears.

Authors(s): D. Reinhart and D. Tyers

Publication: Effects of Winter Recreation on the Wildlife of the Greater Yellowstone Area: a Literature Review and Assessment

Publisher: Greater Yellowstone Coordinating Committee

Publication Date: 0000-00-00

Type:

Location: Yellowstone National Park Wyoming

Abstract: POPULATION STATUS AND TREND Historically, grizzly bears (Ursus arctos horribilis) ranged throughout most of western North America. Today, only a fraction of historic population levels occupy a remnant of their former distribution range (USFWS 1993). Loss or degradation of habitat in conjunction with unregulated hunting and livestock depredation control are cited as the main factors contributing to their decline (USFWS 1993). Grizzly bear populations have persisted only where large areas of public land maintained in a natural state provide necessary habitat components. Limited and/or regulated human activity has proven to be a requirement for the maintenance of grizzly populations (Mattson 1990). Today, there are six recovery zones designated within the conterminous United States (USFWS 1993). One of these zones includes a portion of the Greater Yellowstone Area (GYA), where a self-perpetuating grizzly bear population exists. Under the authority of the Endangered Species Act (ESA), the U.S. Fish and Wildlife Service listed the grizzly bear as a threatened species in 1975. Recovery goals for the Yellowstone grizzly have since been established (USFWS 1993). However, the bear?s longterm future remains uncertain and controversial. Threats to its existence are numerous (Picton et al. 1985, Mattson and Reid 1991, Eberhardt et al. 1994, Eberhardt and Knight 1996). In addition, determining population size and the characteristics used as a basis for trend predictions have been problematic (Schullery 1992, Eberhardt et al. 1994, Eberhardt and Knight 1996). The grizzly bear population declined in the early 1970s following the closure of open garbage dumps and subsequent human-caused mortality around the GYA. Since then, trend data indicate a modest population increase (Eberhardt and Knight 1996). While grizzly bear mortalities, including human-caused deaths, have varied widely in the GYA during the past decade, cub production has increased (Eberhardt et al. 1994, Eberhardt and Knight 1996). A turning point in the earlier trend came in the mid-1980s when government agencies committed substantial resources toward the goal of preventing adult female grizzly bear mortality and protecting important grizzly bear habitat (Eberhardt et al. 1994, Gunther 1996). Human-caused mortality of grizzlies, especially females, continues to be of particular concern in the recovery of this species; direct human-caused mortality is the cause of virtually all grizzly bear population declines and extinctions (Mattson 1993). There are several factors that complicate efforts to deal with this issue. It is impossible to predict the number of bear mortalities that will occur in a given time frame, and the range of variation from year to year can be large. Although the grizzly population may be increasing, human use of the GYA is also increasing. This means the potential for bear?human conflicts and human-caused mortalities persist and will probably grow. Numerous researchers have analyzed grizzly bear mortality data for the GYA (Povilitis 1987, Craighead et al. 1988, Knight et al. 1988, NPS 1988). Their findings indicate that most grizzly bear mortalities since 1974 involve humans and can be classified as either illegal shootings or management-control actions. Povilitis (1987) found that almost half of the mortality risk was associated with people carrying firearms on national forest lands. Within Yellowstone National Park, almost all grizzly bear mortalities were the result of management actions by the National Park Service against habituated, human-food-conditioned grizzlies (Gunther 1994). Knight et al. (1988) reported that known and probable deaths of grizzly bears tend to be centered around specific areas in and around Yellowstone National Park. They described these as ?population sinks? and identified them as the gateway communities surrounding Yellowstone National Park, major development areas within the park, sheep grazing allotments, and various other human concentration areas. One of the major problems associated with human development in occupied bear habitat is the availability of attractants (garbage and human and pet food). Human garbage is cited as one of the major contributors to bear conflicts with humans (Herrero 1985). If food is obtained at one of these sites by a bear, the bear may periodically check the site for more food. The bears that are thus conditioned are often the target of management actions and usually become mortalities. Bears are also killed by illegal shooting. These shootings may be categorized as selfdefense, defense of property, hunters mistaking grizzlies for black bears, and poaching. An increase in people in areas where there are bears increases the likelihood of mortalities by shooting. There are other issues to consider in the long-term status of the Yellowstone grizzly bear. The population may reach carrying capacity, causing a decrease in subadult survival (Eberhardt and Knight 1996). Available food may be reduced by climatic change (Picton et al. 1985, Mattson and Reid 1991), loss of whitebark pine from blister rust infection (Kendall and Arno 1990, Mattson and Reid 1991), and a decrease in Yellowstone cutthroat trout as a result of whirling disease and competition with lake trout (Varley and Schullery 1995). LIFE HISTORY Much is known about the life history of the Yellowstone grizzly bear (McNamee 1984). However, only those details that relate to the topic of winter recreation use will be mentioned here. Cubs are born in the den from late January to early February. They are helpless and rely on the mother for warmth and nourishment. The average litter size is about two (Schullery 1992). This is a time when both mother and offspring are especially vulnerable (Reynolds and Hetchel 1980). HABITAT DENNING In a five-year study of Yellowstone grizzly bears in the late 1970s, November 9 was found to be the mean entrance date for 70 bears tracked to their dens. The earliest entrance date recorded was September 28 for a pregnant female and the latest was December 21. Pregnant females entered dens earliest, but differences in the mean denning dates of sex and age groups other than pregnant females were not significant. Bears frequented the immediate area of den sites from 8 to 22 days before entering (Judd et al. 1986). Male grizzlies were usually the first to leave their dens, emerging between mid-February and late March. The other population segments generally emerged in the following order: single females and those with yearlings and two-year-olds followed by females with new cubs. The last group emerged between early and mid-April (Judd et al. 1986). Judd et al. (1986) concluded that bears did not seek den sites in open areas or show strong preference for a specific type of canopy coverage; however, sites with whitebark pine and subalpine fir appeared to be preferred for dens. Both tree species are found at higher elevations. Elevation of dens ranged from 6,500 to 10,000 feet; and the average elevation was 8,100 feet, with an apparent clumping in the range of 8,000 to 9,000 feet. Dens were found on all aspects, but there was an apparent preference for north exposures. Most dens were found in the 30 to 60 degree slope range. Some dens were reused, but others collapsed after a season of use (Judd et al. 1986). Judd et al. (1986) concluded that availability of denning sites did not appear to be a critical element of grizzly bear habitat in the Yellowstone area since grizzly bears appear to be able to use sites with a wide range of environmental characteristics. In addition, given the amount of protected habitat in Yellowstone National Park and the surrounding national forest wilderness areas as well as the large size of a grizzly bear?s home range, they did not think den sites would become scarce in the foreseeable future. Denning studies in Canada, Alaska, and the Northern Continental Divide Ecosystem (IGBC 1987) indicate that while there are differences in entry and emergence dates, there is commonality in the data on den characteristics. These data also indicate the adaptability of grizzly bears in den site selection and a strong fidelity to denning areas. Although den re-use has been documented in many areas, it is not considered common; however, returning to a denning area is. These denning areas apparently possess characteristics that make them favorable, and some individuals remain traditional in using them (IGBC 1987). PRE-DENNING AND POST-EMERGENCE The activity of grizzly bears before denning and after emergence follows a predictable pattern that is determined by feeding behavior. The food habitats of Yellowstone grizzly bears are summarized in Knight et al. (1984) and Mattson et al. (1991). These investigations show that grizzly bears are opportunistic feeders that use a wide variety of animal and vegetal food items. Although diet varies as much by season as by month, trends are discernible. The main items in the diet of Yellowstone grizzly bears are whitebark pine nuts and ungulates. Grizzly bears obtain a substantial portion of their energy from ungulates in the spring (Mattson 1997). This food source is estimated to be one of the top two sources of energy in the average diet, especially during March, April, May, September, and October (Knight et al. 1984). Carrion scavenged from March through May constitutes a major portion of this ingested meat (Mattson et al. 1991), with peak availability of carcasses occurring around mid-April (Green 1994, Green et al. 1997). In fall, bears aggressively forage to store fat for winter. This pursuit is called hyperphagia and is characterized by a determined attempt to increase calorie intake. The most important fall diet item for Yellowstone grizzly bears are whitebark pine seeds. Because the need for food is so intense, bears may approach areas of human activity that they would ordinarily avoid during this time when whitebark pine seeds are not available (Mattson 1990, Mattson et al. 1992). In spring, bears leave their denning sites at higher elevations and search for carrion from winter-killed bison and elk. Therefore, key spring habitats for Yellowstone grizzly bears are ungulate winter ranges (Mattson 1997). Bear use of ungulate carcasses during spring varies among habitats. Green (1994) found that grizzly bear use of spring carcasses increased with elevation and that bears were more likely to use carcasses in the geothermally influenced habitats of the Firehole?Gibbon and Heart Lake areas than in the low elevation areas of the Yellowstone northern range. This occurred even though most spring carrion in Yellowstone National Park was found on lower elevation ungulate winter range (Green 1994, Mattson 1997, Green et al. 1997). Various studies have indicated that live ungulates are used as food when they are most available and vulnerable, as weakened animals during the spring (Henry and Mattson 1988, Green et al. 1997), as calves during May and June (Gunther and Renkin 1990), or as weakened bulls during the fall rut (Schleyer 1983). A few grizzlies have learned to kill adult elk during the summer (Servheen and Knight 1993). Another high-energy diet item for Yellowstone grizzly bears following den emergence is whitebark pine seeds. Whitebark pine seeds are an energy-rich bear food typically found at higher elevation forest stands during the fall (Mattson and Reinhart 1994). However, after a high whitebark pine cone crop, cones will remain available during the following spring. As a result, bears will forage in these higher elevation habitats, apparently preferring this food item to carrion (Mattson 1997, Green et al. 1997). HUMAN ACTIVITIES Judd et al. (1986) acknowledged that a deficiency in their investigation of grizzly bear denning activity in the GYA was the lack of insights gained on the impact of humans to bears during this period in their lives. The den sites they investigated were remote from humans at all times of the year, and there was no opportunity to address this issue. One of the few studies that did deal with this topic was conducted in Alaska. It considered the impact of winter seismic surveys and small fixed-wing aircraft on denning grizzly bears (Reynolds et al. 1984). Grizzly bears used in the study were radio-collared or had heart-rate transmitters implanted. Potential sources of disturbance included the sounds of aircraft, sounds of operating vehicles (trackmounted drill rigs, geo-phone trucks, survey Bombardiers, snow machines, support trains), and sounds of shock waves associated with the detonation of about 85 pounds of dynamite at approximately 100 feet below the surface. Detonations conducted within a range of 0.8 to 1.2 miles of the bears did not cause them to leave the den. However, movements within dens were sometimes detected following blasts (Reynolds et al. 1984). When seismic vehicles passed within 5/8 mile of the den, the bear?s heart rate was elevated much more often than when undisturbed (Reynolds et al. 1984). Circumstantial evidence indicated that an unmarked bear left its den when seismic activity was within 650 feet of the den, but tractors and tracked vehicles came within 325 feet of a denned female with 3 yearlings without causing den abandonment. Mid-winter over-flights of dens with small fixed-wing aircraft did not change the heart rates of two females denning with young; however, flights conducted closer to the time of den emergence did change the heart rates of bears. The authors concluded that even if animals did respond to noises associated with seismic exploration activities, effects on them were probably minimal at these distances and at this level of activity (Reynolds et al. 1984). None of the radio-collared bears deserted dens, and there was no evidence of mortality. Other research shows varying effects of human use on hibernating bears. Harding and Nagy (1980) documented grizzlies successfully denning on Richards Island, Northwest Territories, in the general area of hydrocarbon mining activity. Of the 35 dens they located, 28 were within the potential impact area, including several within one to four miles of active mine areas. However, Goodrich and Berger (1994) demonstrated that black bears abandoned den sites in response to disturbance. Reynolds and Hechtel (1980) speculated that agitation within the den could have serious consequences for females with newborn cubs. Watts and Jonkel (1989) supported this idea and added that the ability of bears to reduce energy output in the winter may be a function of the secure den environment. In addition, human disturbance during denning could accelerate starvation and has resulted in den abandonment. They concluded that poor quality den sites and adverse weather could elevate metabolic rates and increase energy demands. Also, Geist (1978) discussed the implications of energy expenditure for animals and noted that when they are excited, the energetic costs from increased metabolism and heart rate can be significant. Presumably, this would hold true for bears in a den. By their nature, dens represent locations where bears concentrate activities. This raises the concern of bear?human conflicts around dens. However, there are few documented cases of people being injured by bears in the vicinity of den sites. Herrero (1985) concluded this type of behavior may be due, in part, to the fact that dens are consistently in remote areas less traveled by people. To a greater extent, grizzly bears may be affected by human activity while foraging during the pre- and post-denning periods. The pre-denning and post-emergence periods are critical times for bears. In the first time frame, they are in an intense feeding mode to store fat for the winter, and in the second time frame they are in search of food after depleting their reserves over the winter. POTENTIAL EFFECTS The literature indicates that bears can be impacted by human activities in winter. There are three stages in the annual cycle of the grizzly bear when it is vulnerable to the impacts of winter recreation use: (1) pre-denning, (2) denning, and (3) post-den emergence. Because of this, it is important to address a longer time frame than the traditional winter months. For example, the pre- and postdenning periods for bears overlap the fall and spring seasons, respectively. Therefore, it is reasonable to consider the pre- and postdenning time for bears as biological events instead of restricting an analysis of effects to calendar dates. By the nature of how some recreational facilities are managed, winter visitor use generates effects on grizzly bears in the fall and spring that would otherwise not occur. The existence of winter-use facilities and programs likely encourage additional public visitation in the shoulder seasons. Winter recreational effects on bears are thus contingent on when and where facilities open in the fall and close in the spring. Destruction of den sites or denning habitat does not appear to be a major issue in the GYA at present or in the near future. Neither does disturbing bears while they are preparing or occupying dens, although the possibility exists. The main concern is the potential for bear? human conflicts and displacement of bears while they are foraging during the pre-denning and post-emergence periods. Specifically, this involves bears engaged in wide-ranging foraging efforts before denning, mainly near whitebark pine habitats. It also includes the use of ungulate wintering areas by bears seeking carrion after leaving dens, and, to a lesser degree, bears using over-wintered whitebark pine seed crops at higher elevations. Grizzly bears of the GYA may be affected by human winter recreation use of the following Potential Opportunity Areas: (1) Destination areas. Human activity at destination areas has the potential to negatively impact grizzly bears. This is primarily in the context of the pre- and post-denning periods. For example, spring surveys of grizzly bear habitats have shown that bears generally used carcasses less often than expected within 3 miles of a major park development (Green et al. 1997). Moreover, when bears come in proximity to park developments, more bear management actions and subsequently more grizzly bear removals occur (Mattson 1990, Reinhart and Mattson 1990). Winter destination areas are becoming more popular. They include major ski areas, resorts, developments in Yellowstone National Park, and park gateway communities. These areas have been historic population sinks for grizzly bears in the GYA (Knight et al. 1988). The potential for bear?human conflicts is high when winter developments remain open after bears emerge from hibernation and are using spring habitats (approximately March 15) (Green et al. 1997). This is especially critical when these developments occur in or near areas where winter-killed ungulates and over-wintered pine nut crops may be found (Mattson et al. 1992). In addition, bears will seek attractants around human developments in the pre-denning period of hyperphagia when food is less available. Frequently, the result is bear?human conflicts. Mattson et al. (1992) concluded there is a relationship between the quality of the fall pine nut crop and the number of conflicts that occur. During years of widespread pine nut use, grizzly bears are seldom found in proximity to human facilities. However, during years of little or no pine nut use, areas near human facilities (less than 3 miles from roads and 5 miles from developments) were used intensively by bears. Also, managers trapped nearly six times as many bears and nearly two times as many bears were killed during years of low pine nut production. Presumably, this was a consequence of bears being nearer and in more frequent contact with humans while seeking alternate foods to compensate for the lack of available pine nuts. (2) Primary transportation routes and (3) scenic driving routes. Year-round roads will exist regardless of winter recreation use. However, winter recreational use management may cause changes in the amount of traffic a road receives. It may also be a catalyst for creating new roads. Winter vehicle use of year-round roads during the denning period does not pose a risk to bears. Bears and traffic are spatially separated during most of the winter, and bear behavior seldom brings them into contact with the road corridor. Bear attractants along roads in the pre- and postdenning periods do present a risk. This could occur at roadside trash collection sites or as deliberate feeding of panhandling bears. An additional concern is road-killed animals (usually ungulates or rodents) that may attract bears to the roadside where they are vulnerable to vehicle collision. (4) Groomed motorized routes and (5) motorized routes. Snowmobile traffic alone on highly and moderately groomed routes does not present a significant impact to bears during most of the winter months. This is because of the predictability of defined snowmobile corridors and because most snowmobile use occurs during the time that bears are in hibernation. Conflict could occur when snowmobile use coincides with spring bear emergence and foraging. The potential for bear?human conflicts in Yellowstone National Park during the spring emergence is exacerbated by the fact that park roads are often located near thermal areas where ungulates congregate in the winter. The geothermally influenced ungulate winter ranges in the Firehole, Gibbon, and Norris areas are good examples of locations where the risk of bear?human conflict in the spring is high. (6) Backcountry motorized areas. Most use of ungroomed snowmobile areas should not conflict with bear activity because it coincides with bear hibernation. Moreover, areas of ungroomed snowmobile use typically occur at elevations above bear spring habitats. An exception is when overwintered whitebark pine crops are available, and bears forage at high elevations in the spring. Another possible effect may occur because most backcountry snowmobile use occurs at higher elevations, where most bear denning is found. The potential for conflicts between bears and recreational users does exist when dispersed use occurs after bear emergence (between March 1 and March 15). (7) Groomed nonmotorized routes. Skiing along groomed routes does not present a significant impact to bears during most of the winter months. This is because of the predictability of defined ski corridors and the timing of most skiing coincides with bear hibernation. Conflict could occur when skiing is at the same time as bear foraging in the post-den emergence period. (8) Nonmotorized routes. Skiing and snowshoeing along ungroomed routes does not present an impact to bears during most of the winter months. This is because of the timing of most of this travel coincident with bear hibernation. Conflict could occur when travel coincides with bear foraging in the post-den emergence period. (9) Backcountry nonmotorized areas and (10) downhill sliding. Backcountry skiing, showshoeing, and downhill sliding should not present an impact to bears during most of the winter months. Again, the potential for bear?human conflicts may occur during the late winter period after bears emerge from hibernation. A component of this is the risk of human injury resulting from surprise encounters in backcountry areas as people disperse across the landscape in a manner unpredictable to bears (Herrero 1985). A unique expression of this occurs in low-elevation ungulate winter range where people search for dropped elk antlers. In this case, people intentionally canvas all parts of the terrain and concentrate on areas where wintering and winter-killed elk are found. MANAGEMENT GUIDELINES (1) Destination areas. Early and mid- December and early and mid-March should be used as a time for transition from a fall to winter and winter to spring management strategy, respectively. Appropriate actions include closing facilities, restricting human use in sensitive areas, improving sanitation, and providing public education. Management of developments should reflect recognition of an increased potential each spring for bear?human conflicts and displacement of bears foraging within important habitats. On public land, developments can be regulated, but it is more difficult to address activities at developments on private land. In these cases, coordinated sanitation programs involving private interests and government organizations are needed to remove attractants year-round, with a special emphasis placed on securing attractants during the pre-denning period. (2) Primary transportation routes and (3) scenic driving routes. Good roadside sanitation should be maintained. Signing to inform motorists of the need to secure attractants should be provided. Carcasses should be removed from the roadside between March 1 to November 30. No new roads to accommodate winter recreational use should be built in grizzly bear habitat as more access would ultimately result in more bear?human conflicts. (4) Groomed motorized routes and (5) motorized routes. Grooming and use of snowmobile roads and trails should end by March 15 in areas where post-denning bear activity is high. (6) Backcountry motorized areas. Where winter use occurs in ungulate wintering areas, activity should end by March 15. In areas with whitebark pine forests, a primary issue is the displacement of bears. Because the presence of over-wintered pine nut crops is not consistent, this is an episodic and not an annual concern. Therefore, travel restrictions should be addressed based on yearly monitoring rather than as a continuous restriction. (7) Groomed nonmotorized routes. Depending on the observed risk, grooming and use of these routes should end between March 1 and March 15 in those areas where bears would potentially be drawn to forage. Sanitation procedures around associated support facilities should be strengthened and public education initiated during the same time frame. (8) Nonmotorized routes. Use should be curtailed or restricted depending on the observed risk between March 1 to March 15. Public education should be initiated during the same time frame. (9) Backcountry nonmotorized areas and (10) downhill sliding. Use should be curtailed or restricted depending on the observed risk between March 1 to March 15. Public education should be initiated during the same time frame. (text continued on website)

Keywords: animal, carnivore, bear, mammal, Ursidae, Ursus arctor horribilis, grizzly bear, human activity, hunting, livestock, habitat, behavior, distribution, wildlife, management, population, mortality, bibliography , Greater Yellowstone Ecosystem, suburban area, poaching, food, den, denning, radio collar, rodent, ungulate, bison, elk, wapiti, predation, forage, Bridger-Teton National Forest, Jackson Hole, Teton County, Sheep, fish, Yellowstone cutthroat trout, Oncorynchus clarki bouvieri