Effects of winter recreation on elk

Authors(s): W. Clark

Publication: Effects of winter recreation on wildlife of the Greater Yellowstone Area: a literature review and assessment. Report to the Greater Yellowstone Coordinating Committee. Yellowstone National Park, Wyoming.

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Publication Date: 0000-00-00

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Abstract: POPULATION STATUS AND TREND By the early 1900s, elk (Cervus elaphus) populations throughout North America had been decimated by commercial exploitation, competition with domestic livestock, and habitat changes. Most of the estimated 50,000 remaining elk were concentrated in the Yellowstone National Park (YNP) and Jackson Hole areas (Seton 1927). Protection of wildlife in YNP through installation into Yellowstone of the U.S. Army in 1886 and passage of the Yellowstone Park Protection Act in 1894 helped to reduce illegal killing in the park, and by the early 1900s the park?s elk population began to stabilize or increase in number (Houston 1982, Robbins et al. 1982). Conflicts with livestock operations, combined with a series of severe winters that resulted in heavy losses of elk, caused continued concern about the future of the elk population that wintered in the Jackson Hole area (Robbins et al. 1982). In response to these concerns, Congress in 1912 passed legislation authorizing creation of the National Elk Refuge (NER) in Jackson Hole. Since the early 1900s, when management efforts were directed primarily at preserving and enhancing elk populations in the Greater Yellowstone Area (GYA), the management of elk populations has undergone several phases. In YNP, predator control, winter feeding, and effective protection from poaching resulted in a stable or increasing elk population (Houston 1982), which, in turn, created concerns about habitat degradation. Beginning in the 1930s and continuing until 1969, an average of 327 elk per year were removed from the park (Houston 1982), mainly from the northern range, through trapping for translocation and shooting. In 1969, the park placed a moratorium on elk removals (Cole 1969). That period marked the beginning of a management philosophy that continues to the present, in which the park has attempted to allow natural processes, to the maximum extent possible, to regulate ungulate numbers within Yellowstone. After the NER was established in Jackson Hole, the elk population there began to stabilize, although the number of elk in the adjoining Grand Teton National Park (GTNP) continued to decline until mid-century (Smith and Robbins 1994). Managers have been concerned about the large numbers of elk wintering on a restricted area in the NER and the impacts that they may have on forage supply and habitat quality. Therefore, an elk hunt was established on the refuge and in a portion of the adjoining GTNP (Smith and Robbins 1994). The states of Montana, Idaho, and Wyoming manage elk herds in the GYA by monitoring herd numbers and often herd composition, setting population and habitat objectives, and conducting regulated hunts. All of the elk herds in the GYA are subject to hunting in at least a portion of their ranges. Some elk that summer in YNP, which is closed to hunting, may be hunted as they migrate south to winter range (Smith and Robbins 1994). Most of the elk herds in the GYA were either stable or increasing during the 1980s (USFWS 1994), although a few have experienced declines in recent years. Populations south of YNP have been at or above stated population objectives in recent years. Currently, an estimated 50,000?60,000 elk inhabit the GYA, in 10?12 separate herds (USFWS 1994). The northern Yellowstone elk herd summers in the northern and eastern portions of YNP and surrounding mountains, and as far south as Yellowstone Lake (Houston 1982). This herd?s winter range extends from the Lamar Valley in the northeastern corner of YNP, north and west to the Dome Mountain Wildlife Management Area outside YNP (USFWS 1994). This herd numbered around 20,000 in the early 1990s (USFWS 1994), but counts in 1998 and 1999 indicate that the northern herd currently numbers around 12,000 animals (Montana Fish, Wildlife and Parks, unpublished data; National Park Service, unpublished data). A migratory herd of approximately 3,000? 4,000 elk summers in the northern mountains of YNP and moves into the southern portion of the Emigrant elk management unit north of YNP during winter (MFWP 1992). This herd, which has been increasing in recent years, joins a resident herd of approximately 800? 1,000 elk that summers in the Absaroka Mountains north of Yellowstone and winters in the foothills east of the Yellowstone River, north of YNP (MFWP 1992). Three herds inhabit the area to the west and northwest of YNP. The Madison?Firehole herd resides year-round in the Madison and Firehole river drainages within and adjacent to the western boundary of YNP. Numbering approximately 600?800 animals (USFWS 1994), this herd is generally non-migratory (Craighead et al. 1973). Geothermal sites and thermally influenced areas are critical to the overwinter survival of this herd, which winters in a harsh area where snow depths peak at 115?150 cm annually (Craighead et al. 1973, Pils 1998). The availability of thermally influenced areas with associated reduced snowdepths may provide an upper limit to the size of this herd (Craighead et al. 1973). Another population of elk summers in the Gallatin and Madison ranges within YNP and west of the YNP western boundary and winters east of the Madison River in the foothills of the Madison Range (USFWS 1994). This population is believed to be increasing and was estimated at nearly 7,000 in 1992 (MFWP 1992). The Gallatin herd summers primarily in the northwest corner of YNP and winters along the Gallatin River in the Gallatin Canyon area in Montana (USFWS 1994). This herd numbers approximately 1,200?1,400 animals (MFWP 1992). Wildlife managers are concerned about increasing development on this herd?s winter range in addition to a lack of security cover (MFWP 1992). A sub-population of the Gallatin herd summers at high elevations along the Gallatin Mountain Range and in the northwest corner of YNP (USFWS 1994). This group winters in the mountainous areas west of the Yellowstone River and northwest of the YNP boundary. The total Gallatin area elk population was estimated at about 2,900 during the early 1980s (USFWS 1994), and had increased to approximately 3,600? 3,800 by 1992 (MFWP 1992). Three elk herds along the eastern boundary of YNP summer primarily in the park. The Clark?s Fork herd winters along the Clark?s Fork River northwest of Cody, Wyoming, and numbered approximately 3,600 animals in 1988 (USFWS 1994). The North Fork Shoshone herd winters along the North Fork Shoshone River drainage west of Cody, Wyoming. This herd was estimated at roughly 2,900 elk in the late 1980s (USFWS 1994). The Carter Mountain herd winters in the Carter Mountain area and along the South Fork Shoshone River southwest of Cody, Wyoming, and consists of approximately 3,100 elk (USFWS 1994). To the south and southwest of YNP and GTNP are three elk herds that spend all or part of the year in the GYA. Elk from the Targhee herd south of YNP summer generally outside YNP and winter along the Idaho?Wyoming border south of YNP (Mack et al. 1990). Approximately 500 elk were counted in the Targhee herd in the late 1980s (USFWS 1994). The Jackson herd, which winters on the NER and in the Gros Ventre River Valley, summers in the mountains to the north and east, including areas in Yellowstone and Grand Teton national parks and portions of the Bridger?Teton National Forest (Mack et al. 1990, Smith and Robbins 1994). From 1978 to 1982, roughly 7,600 elk wintered on the NER annually (Smith and Robbins 1994). The entire Jackson elk herd was estimated at approximately 16,000 animals in 1988 (USFWS 1994). The Sand Creek elk herd in eastern Idaho, which numbered approximately 4,200?4,900 in the mid- to late 1980s, summers east of Highway 20 in or near YNP, and winters in the Sand Creek winter range southeast of Dubois, Idaho (Brown 1985). LIFE HISTORY Elk are gregarious animals, and for most of the year males and females remain grouped in separate herds. Females begin to restrict their range and gather in traditional rutting areas in August and September (Martinka 1969), where, by early October, they are joined by males (Nowak 1999). During October males compete for females and attempt to gain and hold a harem of females through displays involving high-pitched bugles, antler thrashing, urine spraying, and fighting (Murie 1951, Geist 1982, Nowak 1999). Males may incur serious injury during the rut, which is usually done by late October. Many elk populations in the western U.S. migrate to low elevation winter range (Nowak 1999), where they may aggregate in groups of up to several thousand animals (Boyd 1978). The gestation period is roughly 250?265 days (Clutton-Brock et al. 1982, Taber et al. 1982), after which usually a single calf is born, generally in late May or early June (Murie 1951, Peek 1982). Sex ratio at birth is usually 1:1 (Peek 1982). Females may separate themselves from the larger herd to give birth in isolated areas, where they remain with their calves for several weeks (Boyd 1978). Lactation may last 4?7 or more months (Nowak 1999). Females generally attain sexual maturity at about 2? years of age, and then are capable of producing a calf annually (Nowak 1999). Males are capable of mating at the same age, but most do not successfully breed until much later because of competition from older bulls (Nowak 1999). In wild populations few elk live longer than 12?15 years, with males often living shorter lives than females because of injuries incurred during the rut and decreased ability to deal with poor forage condition during the winter when they are nutritionally stressed from the rut (Peek 1982, Nowak 1999). In heavily hunted populations, the ratio of adult bulls to adult cows may be quite low (Peek 1982). The major source of mortality in most elk populations, including those in the GYA, is hunter harvest and associated crippling loss and illegal kills (Peek 1982). Wolves, cougars, and occasionally coyotes and domestic dogs may prey on both adult and calf elk (Murie 1951, Hornocker 1970, Carbyn 1983, Murphy et al. 1992, Gese and Grothe 1995). Both black and grizzly bears may be an important predator on elk calves in some areas (Murie 1951, Singer et al. 1997). Other sources of mortality are drowning, miring in thermal mud, fighting during the rut, entanglement in fences, and starvation (winterkill) (Murie 1951). Vehicle collisions also contribute to elk mortality in most GYA herds. HABITAT Skovlin (1982) described the basic requirements of elk habitat. Habitat selection is determined by topography, weather, vegetational cover, and escape cover. Elevation is probably the most important topographic influence, determining seasonal availability of habitats. The most important influences of weather on elk habitat use are snow depth and condition, which limit elk movement and forage availability. Vegetative characteristics that are important determinants of elk habitat use include cover for both thermoregulation and hiding or escape, as well as forage availability. Elk are an ecotone species (Skovlin 1982). Studies have shown that although elk are primarily grazers, their use of an area was higher when shrubs were intermixed with forest stands or where forest stands contained more than one successional stage (Lonner 1976). Ecotones provide a greater variety of forage plants used by elk, and more plants occur at a variety of phenological stages because of differences in microclimates where habitat types are intermixed (Skovlin 1982). With the exception of the population in the Madison River drainage in and adjacent to YNP (Craighead et al. 1973), elk in the GYA are migrators, tending to return to the same winter and summer ranges year after year (Peek 1982). Although they are not migratory, the Madison River elk do exhibit seasonal changes in habitat use (Craighead et al. 1973). Migrating elk often follow the same travel routes, which are determined by topographic features and natural travel lanes (Adams 1982). Although movement to winter range is dictated primarily by increasing snow depth and density at higher elevations (Adams 1982, Farnes et al. 1999), summer and winter ranges fulfill differing habitat needs for elk. SUMMER RANGE Because of their large body size, elk have a relatively slow fattening rate, so summer range and the pulse of vegetative productivity between spring and the rut in autumn is of great importance in their ability to build up reserves with which to survive the winter (Geist 1982). Adult female elk face serious energy demands during lactation (Nelson and Leege 1982), which occurs while they are on spring and summer range. Grass is the most important forage type for elk during the spring greenup months, usually making up more than 85 percent of their diet (Nelson and Leege 1982). Grasses, forbs, and browse are all used to varying degrees during the summer, depending on availability (Kowles 1975, Nelson and Leege 1982). Leaves of browse species may also be consumed (Peek 1982). In addition to providing high quality forage, spring and summer range must provide opportunities for escape from biting insects as well as shade for escape from heat stress. Interspersion of cover to open areas appears to be important in determining calving areas because of the need for hiding sites used by newborn calves (Peek 1982). WINTER RANGE Snow depth and snow characteristics appear to be the driving factors in the timing and rate of elk migration to winter range (Lovaas 1970, Adams 1982). Characteristics important in elk use of winter range include areas of low snow cover to facilitate movement and access to forage, escape cover from predation, and security from harassment and associated energy expenditures. Areas used by elk in winter are often low elevation valleys where snow accumulations are low, but may also include windblown ridgetops and thermal areas and thermally influenced habitats where snow depths are generally low and some green vegetation may be found year-round (Craighead et al. 1973). Adult females, calves, and younger elk of both sexes generally winter in large groups in low elevation habitats (Adams 1982). Some females calve while on winter range, in which case hiding cover for calves is of critical importance as described above. Adult male elk generally seek widely dispersed small patches of habitat providing nutritious forage that will build up lost energy reserves and recover from injuries incurred during the rut (Geist 1982). Bulls are often found on the fringes of winter range occupied by cow/calf groups (Peek 1982) or at higher elevations and in areas of greater average snow depth. This separation of the sexes on the winter range may help to reduce competition for limited forage (Peek 1982). Elk diets on winter range are influenced strongly by forage availability, which is in turn affected by snow depth and density. In general, elk prefer to consume dried grasses during the winter, followed in preference by browse species and then conifers (Nelson and Leege 1982). HUMAN ACTIVITIES Elk face many obstacles in surviving the winter, some of which can be compounded by the impacts of human activities. Winter is an energetically difficult time, in which elk must carefully balance energy expenditures against energy intake in order to survive. Forage quality is lower in the winter than at any other time of year. In experimental feeding trials most elk lost weight on diets that mimicked winter diets (Nelson and Leege 1982). Winter habitat quality may play an important role in the reproductive success of females. The overwinter nutritional condition of elk has been correlated with reproductive success. Thorne et al. (1976) correlated high winter weight loss in pregnant females with prenatal calf loss, low calf birthweight, and low survival of newborns. Poor winter diet may also be associated with poor milk production (Taber et al. 1982). Adult males usually enter the winter in relatively poor condition and often injured as a result of rutting activity in the fall (Geist 1982). Quality of winter habitat alone may determine whether some males survive the winter, when forage quality is at its lowest and often is least accessible (Geist 1982). Up to approximately 87 percent of the daily forage consumed by an elk in winter is used for standard metabolic function, leaving less than 15 percent for growth, reproduction, temperature regulation, and activity (Nelson and Leege 1982). Because of the low quality of winter forage, elk often rely on reducing energy expenditures to increase their chances of surviving and successfully reproducing (Marchand 1996). Movement through snow is energetically costly for elk, becoming considerably more costly as snow depth exceeds knee height (Halfpenny and Ozanne 1989). Farnes et al. (1999) reported that when snow-water equivalent, a measure of snow density, reaches 6 inches, elk are generally unable to continue foraging in that area and must move to areas of lower snow depth or density. Elk are apparently unable to crater through snow deeper than approximately 40 cm in search of food, and at greater depths they may switch to foraging on browse (Marchand 1996), which is generally a poorer quality food than grasses. After elk have foraged in an area, the disturbed snow around craters often becomes very dense and precludes further foraging in that area, forcing elk to seek other areas or other sources of food (Farnes et al. 1999). Elk rely on fairly restricted winter ranges in which food and cover may be limited or of marginal quality, and, consequently, any activity preventing them from using all or part of that range could have negative impacts on their ability to survive or to successfully reproduce. In many areas within the GYA historic winter range has been settled by humans and converted into developments or agricultural uses. Human settlement on historic winter range may decrease the quality or availability of winter range, through changes in habitat, increased harassment by humans, or competition with livestock (Skovlin 1982, Taber et al. 1982). The NER was created in response to the fact that much of the historic winter range in the Jackson Hole area had been converted to agricultural and other uses, depriving elk of critical habitat needed to survive the winter. Human settlement in the GYA may already have restricted some elk herds to smaller or less productive winter ranges, putting them at greater risk of negative impacts from other forms of disturbance or displacement. Cows with calves generally winter at lower elevations than do bulls (Adams 1982), but low elevation valleys and river corridors are also the areas most often used by humans for settlement, agriculture, and road-building (Glick et al. 1998). Elk in the Madison?Firehole elk herd are extremely restricted during the winter, surviving in small patches of thermally influenced habitat along the Madison and Firehole river corridors (Craighead et al. 1973, Aune 1981). The groomed road between West Yellowstone and Old Faithful, however, transects the core of this critical winter habitat (Aune 1981). Some research has been conducted into the effects of disturbance on elk behavior and movements. Elk in some areas have apparently changed traditional travel routes in response to human settlement and to hunting pressure, particularly on winter range (Picton 1960, Kimball and Wolfe 1974, Smith and Robbins 1994). Logging activity in some areas has increased year-round access for recreationists into elk habitat, which in some areas has resulted in changes in elk distribution (Skovlin 1982). Declines in elk use of areas within 0.25?1.8 miles of roads have been reported, with distances varying according to the amount and kind of traffic, quality of the road, and density of cover adjacent to the road (Lyon and Ward 1982). Avoidance of roads results in habitat near roads becoming effectively unavailable to elk (Lyon 1983). Ward et al. (1976) and Hieb (1976) state that harassment can be of concern because elk will readily desert productive habitats when disturbance is excessive. When elk groups crossing highways en route to winter range are interrupted by traffic, they have been observed spending a great deal of time searching for the rest of the group before continuing directional travel (Adams 1982). Logging roads with associated debris piled along the edges have proven to be barriers to elk movements in some areas (Lyon and Ward 1982). This is likely to also be true of snow berms piled along plowed roads during the winter. Elk flight distances in reaction to humans varies by season, habitat, conditioning, and type of human activity (Skovlin 1982). When elk are disturbed by hunters, they may travel long distances before stopping (Adams 1982), sometimes up to 8 miles before reaching security cover or protected areas (Altmann 1958). Solitary elk appear to have longer flight distances than do groups (Skovlin 1982). Elk experience an accelerated heart rate during the alert state immediately preceding flight caused by harassment, car horns, gunshots, and sonic booms (Ward and Cupal 1979), but elevated heart rate has rarely been linked to changes in reproduction or survival (Ferguson and Keith 1982). Repeated flight, however, particularly through deep snow, uses energy reserves that might otherwise be used to help elk survive the critical final weeks of winter (Skovlin 1982). Lyon and Ward (1982) reported that logging activity occurring on elk winter range results in less movement by elk than logging activity on summer range does, possibly due to the reduced vigor of elk during winter, the difficulty of movement in deep or crusted snow, and the lack of alternative areas to which to move. Aune (1981) also observed that in YNP, elk were less likely to flee from snowmobiles or skiers late in the winter than they were earlier in the season. He suggested that this was likely due in part to habituation by elk to snowmobile traffic, and in part to decreased vigor of elk later in the season combined with the increasing difficulty of flight through deep, crusted snow. Proximity of escape cover that breaks the line of sight between elk and the disturbance may reduce flight distances and consequently the amount of energy used in flight. Moving automobiles and trail bikes had little effect on elk resting in timber at distances of only 0.13 miles (Lyon and Ward 1982). Findings from studies of elk behavior in response to specific human winter recreational activities are varied. Ferguson and Keith (1982) researched the influence of crosscountry ski trail development and skiing on elk and moose distribution in Elk Island National Park in Alberta, Canada. They found no indication that overwinter distribution of elk was altered by cross-country skiing activity. However, it did appear that elk moved away from ski trails, particularly those that were heavily used, during the ski season. Anecdotal observations indicate that elk may be relatively sensitive to the sight and sound of snowmobiles, moving away when only a few machines are present (Bureau of Land Management, unpublished data in Bury 1978). Anderson and Scherzinger (1975) reported that when recreational snowmobile activity increased in the Bridge Creek Game Management Area in northeastern Oregon, winter elk counts decreased by 50 percent. After the area was closed to snowmobiling, the population returned to its previous numbers. Aune (1981) found that heavy snowmobile traffic in YNP occasionally inhibited free movement of wildlife, temporarily displacing them from certain areas. The most significant impact on wildlife distribution appeared to be within 60 m of groomed snowmobile trails. Aune (1981) also reported that snowmobile activity in YNP resulted in average elk flight distances of 33.8 m, compared to average flight distances of 53.5 m in response to skiers. In another study, elk began to move when skiers approached to within 15 m in an area heavily used by humans year-round, and within 400 m in an area where human activity is much lower (Cassirer et al. 1992). Elk in YNP fled more frequently and over greater distances from skiers off established trails than from skiers on established trails (Aune 1981). During winter in Rocky Mountain National Park, elk were relatively undisturbed by visitor activities occurring on roads, but they exhibited longer flight distances from an approaching person than from an approaching vehicle (Shultz and Bailey 1978). Ward (1973) reported that elk are easily conditioned to repeated patterns of human activity, but tend to be disturbed by deviations from normal patterns. In YNP, Aune (1981) found that wildlife species, including elk, were more likely to be displaced by or exhibit flight responses to snowmobile traffic during the preseason when traffic was limited to occasional administrative travel than they were to the heavier traffic occurring during the recreational season. This may have resulted from habituation by elk to the presence of snowmobile traffic and to establishment of a more constant traffic pattern during the recreational season. This change in response may also have resulted from decreasing physical condition of elk later in the winter, and increasing snow depth and crusting that inhibited flight. Elk also demonstrated a shift to a more crepuscular activity pattern when recreational snowmobile activity increased (Aune 1981). It has been suggested that the presence of groomed ski and snowmobile trails may provide a means for energy efficient travel for elk and other wildlife during winter. Ferguson and Keith (1982) found no indication that elk used groomed ski trails as preferred travel routes in Elk Island National Park, Alberta. Elk in the Madison?Firehole and Gibbon River corridors of YNP used groomed snowmobile trails increasingly as snow became deeper and more crusted and as animal condition declined through the winter (Aune 1981). Trails created by only one or two passes of a snowmobile and ungroomed ski trails, however, were not compacted sufficiently to support the weight of an elk and consequently were not used. Elk suffer greater chances of mortality from vehicle collisions when using roads and trails, particularly if they become trapped by plowed snow berms or other obstacles along road and trailsides. POTENTIAL EFFECTS Winter recreational activity can result in a variety of impacts on elk, depending on the nature and duration of the activity and the condition of the affected animals. Elk may readily habituate to predictable activity, so that recreational activities taking place on wellestablished routes and over a predictable time interval may have little effect on them after they become accustomed to the activity. Elk may learn to avoid areas of continual noise or disturbance, however, effectively removing a portion of otherwise available habitat from their use. This avoidance can have negative impacts on elk by reducing the amount or type of forage available and thereby adding to nutritional stress. Human activity occurring in low-snow areas may impact elk primarily because those areas are likely to be favored by elk late in winter when they are in poor condition. Antler hunting, for example, is an extremely popular activity during the late winter in many portions of elk habitat in the GYA, particularly on the northern range. This activity places humans generally on foot or horseback in low-snow winter range areas where bulls may be concentrated late in winter. The generally unpredictable, off-trail nature of this activity has the potential to create significant disturbance and stress to bull elk at a time when their energy reserves are at their lowest. Conversely, elk may learn to use groomed roads or trails, and plowed roads as energyefficient travel routes during the winter. It is not known whether the energy savings of using plowed and groomed roads and trails is greater or less than the costs of disturbance encountered while using such travel routes. Plowed roads may represent barriers to movement by elk if there are high snow berms on either side of the road, and may contribute to vehiclecaused mortality of elk using roads or trails. Roads may also provide energy efficient means of travel for predators in winter, increasing their ability to access prey and thereby increasing vulnerability of prey species such as elk. Activities occurring in unexpected places or at unexpected times, such as skiing on lightly used trails or off-trail skiing, off-trail snowmobile use, or opening of previously closed areas can cause elk to flee, thereby using valuable energy reserves. Flight may be particularly costly for elk if snow is deep or crusted, or if elk are already in nutritionally stressed condition. Activity that occurs repeatedly but unpredictably may result in cumulative energy use over the course of the winter that might compromise an elk?s ability to survive or reproduce. Repeated disturbance that does not result in flight may create stress in the form of increased heart rate and hormonal and other physiological changes, but any effects that these changes may have on overall survival and reproduction have not been well researched. The effects of disturbance by humans may be lessened if adequate hiding cover is available nearby. Disturbances that occur late in winter, when elk are in their poorest physical condition and the forage supply may be depleted, are likely to have a more negative impact than those occurring earlier in winter. Inability of elk to move through late-winter deep and crusted snow may compound the stress associated with disturbance at that time. text continued in website

Keywords: animal, mammal, ungulate, Cervidae, Cervus elaphus, elk, wapiti, Yellowstone National Park, Jackson Hole, Grand Teton National Park, National Elk Refuge, Teton County, livestock, grazing, human activity, habitat, hunting, population, mortality, bibliography