Effects of winter recreation on moose

Authors(s): D. Tyers

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: The distribution of moose (Alces alces) corresponds to environments where snow is a dominant feature in the winter. Moose are anatomically and behaviorally suited for areas where winter conditions can be harsh. These are often the same areas where humans pursue winter recreational activities. Because of this, there is a strong potential for some types of winter recreation to affect moose. POPULATION STATUS AND TREND Moose may have been rare in western North America during historic as well as pre-Columbian times (Peterson 1955, Kelsall and Telfer 1974, Kay 1997). However, since about 1900 moose appear to have extended their range and/or become more numerous (Kelsall and Telfer 1974, Kay 1997). Estimating moose population size has proven to be a consistent problem in many areas (Timmermann 1974, 1993; Gasaway et al. 1986), and a lack of accurate estimates has hampered good management (Gasaway et al. 1986). Some attempts to determine moose population status and trend in the Greater Yellowstone Area (GYA) have been equally problematic (Tyers unpublished data, Gasaway 1997), and a good count for this region has not been achieved. Although demographic data are not available at a large landscape level, it is known that moose are uncommon compared to other ungulates in the GYA. In addition, populations are often at low density. In these circumstances, a conservative approach to moose population management is advised (Tyers unpublished data, Gasaway 1997, Karns 1997). Some information on moose populations in the GYA is available. Houston (1982) reported that moose remains have not been found in archeological sites in northwest Wyoming or south central Montana. He concluded that moose had not yet occupied northwest Wyoming in 1830 (Houston 1968), but had colonized the Yellowstone area by the 1870s; they appeared on Yellowstone?s northern range around 1913 (Houston 1982). Schullery and Whittlesey (1992) reviewed the documentary record for wolves and related wildlife species in the Yellowstone National Park area prior to 1882. Based on historic accounts, they concluded that moose were common in the southern part of the park in 1882, and rare sightings were made near or on the northern range about the same time. Recent studies indicate a population decline following the 1988 Yellowstone fires in areas where fire effects were severe and in areas where moose rely on older lodgepole pine forests for winter range (Tyers unpublished data, Tyers and Irby 1995). In response to these data, Montana Fish, Wildlife and Parks has significantly reduced hunting quotas in districts north of Yellowstone National Park (T. Lemke, Montana Fish, Wildlife and Parks, personal communication). In portions of the GYA where moose have different winter-use patterns or where fire effects are not an issue, the trend may be different. Several hypotheses have been proposed to explain the biogeography of moose in western North America. Kelsall and Telfer (1974) presented five hypotheses to explain the relatively recent expansion of moose. These include: (1) moose have had a limited amount of time to colonize North America since the last glaciation; (2) climatic variation?the Little Ice Age and associated severe winter weather limited moose populations around 1700?1800; (3) disease once limited moose numbers; (4) European settlement modified the original climax forests, which were poor moose habitat, and created seral vegetation types that moose prefer; and (5) predators once limited moose, but the near extermination of native carnivores allowed moose to extend their range and expand their populations. Kay (1997) proposed a sixth hypothesis: moose were extremely vulnerable to predation by Native Americans who had no effective conservation practices. The result was a control of moose biogeography by native hunting. Loope and Gruell (1973) proposed a seventh hypothesis specific to the GYA: a very low moose population during the 19th century was the result of fires, which maintained early successional vegetation. They speculated that moose populations have increased in this century in northwest Wyoming as forests have matured under a management policy of fire suppression. A primary factor in this, they believe, is an increase in subalpine fir, a shadetolerant species found in older forests. They further hypothesized that subalpine fir is the staple food item in the diets of moose in the area. Tyers (unpublished data) tested this hypothesis and demonstrated that moose along the northern border of Yellowstone National Park feed primarily on subalpine fir saplings in older lodgepole forests. Although the Shiras moose is a relatively recent arrival to the GYA, available habitat is now occupied. However, future population trends are uncertain. Habitat conditions, human influences, and exposure to predation vary considerably across the GYA. In addition, the small home range size of moose and the strong fidelity moose show to a geographic area tend to create many fairly discrete populations. For these reasons, it is likely that local populations will display very different trends. As evidenced by the hypotheses for recent moose range expansion explained above, future trends in the GYA will be largely determined by predation and habitat quality. Humans, bears, and wolves prey upon moose in the GYA. The recent reintroduction of wolves is an important variable with unknown consequences. Some have speculated that wolves will play a major role in regulating moose populations, and a decrease in moose numbers will be noticed (Messier et al. 1995). The 1988 Yellowstone fires were a landscape-level disturbance that affected the successional stage of vegetation. This will undoubtedly be a determining factor for moose populations in a large spatial and temporal context. In many parts of the GYA, a return to an early successional stage represents a decrease in moose winter habitat that will reduce carrying capacity (Tyers unpublished data). Riparian areas with deciduous vegetation are important foraging areas for moose. They are limited in size and distribution and are particularly vulnerable to human impacts. Management of these areas will also play a role in determining moose population trends. LIFE HISTORY Moose are seasonal breeders with the mating season in the fall and calving in the spring. Most cows ovulate for the first time between 16 to 28 months of age, although those in populations on poor range may not breed until 40 months. Most cow moose produce either single or twin calves. Twinning varies widely across North America and may be correlated to habitat quality and carrying capacity. Triplets have been reported but are rare. Most cows produce a calf or calves each year. Neonatal predation is common and can be high (Schwartz 1997). Average life span is highly variable; generally, it may be 7 or 8 years with a maximum age at possibly 20 (Ballard and Van Ballenberg 1997). HABITAT As a generalization, the moose is an animal of the boreal forests?the coniferous forests that occur in a broad band across northern North America and Eurasia. Boreal forests also extend southward at higher elevations in the mountains. The climate within this biome is characterized by cold winters and short, mild summers (Brewer 1994). Food and cover are the primary factors limiting geographic distribution in the north (Kelsall and Telfer 1974), and climate is the factor in the south (Reneker and Hudson 1986). The most critical factor, especially to the southern distribution of moose, is temperature (heat) (Karns 1997). Moose are browsers?herbivores that eat primarily shrubs and trees (Peterson 1955, Renecker and Schwartz 1997). Specifically, they eat twigs and foliage high in cell-soluble sugars that ferment readily in the rumen. These are foods that are considered to be, comparatively, of poor quality. In addition, they are characterized as concentrate selectors. Because of their body size, they require large amounts of abundant food to survive. To satisfy this need, they seek out concentrations or patches of biomass in the environment where they can spend relatively long periods of time foraging. For example, moose seek out or select willow (Salix spp.) that often offers large amounts of forage bunched together on the landscape. Because of their dietary constraints, the quantity of biomass for foraging determines moose density. The large body size of moose is an advantage in boreal regions for coping with predators and periods of extreme cold and deep snow (Renecker and Hudson 1986, 1989). However, it also imposes limitations on activities. Moose have a difficult time dissipating heat, and heat stress can lead to a reduction in overall activity during warm periods. Ambient air temperatures above 23? Fahrenheit in winter and above 57? Fahrenheit in summer can be stressful and can cause moose to seek cooler areas. In a broader sense, problems with thermal regulation restrict range expansion into more temperate climates. Telfer (1984) placed moose habitat in six broad categories: boreal forests, mixed forest, large delta floodplains, tundra, subalpine shrub, and stream valleys. These may be further described as either permanent or transitory in nature (Geist 1971, Peek 1997). Permanent habitats are those that persist and do not succeed over time to a different pattern of vegetation. For example, alluvial habitats are dynamic in that flooding and streambed alteration produce a constantly changing system, but they are permanent in the sense that the same type of vegetation is present after a disturbance. Boreal forests are more transitory. Fire can radically alter the vegetative composition; a mature forest can be changed to a shrub community. The shrub community will eventually be dominated by a forest that is vulnerable to a fire event just as the first one was. The pattern is cyclic, and each successional stage is transitory to the next. Throughout much of their range, moose are found in transitory habitats. Specifically, they are closely linked to early seral stages where shrub biomass is plentiful (Dryness 1973, Wittinger et al. 1977, Irwin and Peek 1979). In many areas, moose benefit from the removal of the forest canopy (Taber 1966, Krefting 1974, Kelsall and Telfer 1974, Leresche et al. 1974, Irwin 1975, Peek et al. 1976). Disturbances such as fire, logging (or other forms of mechanical manipulation), disease, or wind events can create favorable moose habitat by removing trees that compete for resources with shrubs. However, it is also known that moose winter habitat-use patterns can be highly variable between regions and years (Peek 1974a), which reflects adaptive responses to different environmental conditions. Peek (1974a) cautioned against making unequivocal generalizations about moose winter habitat selection and suggested that the amount of variability can make these descriptions misleading. Included are statements about the role of transitory habitats, forest canopies, and seral stages in moose habitat. He stated that this variability has special consequences to management because it is important to determine the forage species locally preferred by moose and then favor those species through management actions. Snow conditions have an important influence on moose habitat-use patterns (Peek 1997). Conditions include temperature, density, hardness, and depth (Peek 1997), and factors that affect the ability of moose to access browse (Peek 1971, Schladweiler 1973). The presence or absence of a forest canopy can have a significant effect on snow conditions. For example, moose often prefer open brush fields for foraging where browse is abundant. They have also been known to seek coniferous forests when snow conditions impeded movements in open areas (des Mueles 1964, Kelsall 1969, Telfer 1984, Peek et al. 1976, Rolley and Keith 1980, Thompson and Vukelich 1981). Travel in forests is often less energy demanding because tree branches ameliorate snow density, hardness, and depth through shading and intercepting falling snow. Several studies have reported specific snow depth thresholds for moose. Snow depths of 25.5 inches have been reported to affect habitat use and movements of moose (Kelsall 1969, Thompson and Vukelich 1981, Pierce and Peek 1984). In Quebec, des Mueles (1964) found that moose shifted to more dense coniferous areas when snow depth reached 30 to 34 inches, and moose did not use areas where the snow exceeded 42 to 48 inches, even when the snow was soft. Kelsall (1969) reported moose were severely restricted by snow depths of 27.5 to 35.5 inches. Kelsall and Prescott (1971) found that when snow depths reached 38 inches in New Brunswick moose where confined to areas with high forest canopies. Tyers (unpublished data) demonstrated that moose on Yellowstone?s northern range avoided snow depths greater than 31.5 to 43 inches and were not found when snow exceeded 54.5 inches. Peek (1974a) reported on the variability in the winter habitat used by moose in North America. He reviewed 41 different reports: 13 from the Intermountain West; 6 from Alaska; and 22 from Canada, Minnesota, and Maine. His review highlighted the variation and commonality in the diet and forest successional stage used by moose. In another document (1974b) he focused on the Shiras moose. He identified five different types of winter habitat for the Shiras moose in the Intermountain West, an area that includes the GYA: 1. Willow bottom/stream/conifer complex occurring along high-gradient streams. 2. Flood plain riparian community containing extensive willow stands. 3. Drainages where willow-bottom communities are very limited and are of little importance to moose, but where conifer and aspen types are important, and the diet is more varied than in areas where willow is plentiful. 4. Arid juniper hills. 5. Willow communities that are important but are neither limited nor extensive. Moose are forced from these areas by snow conditions into adjacent forested slopes where subalpine fir stands support low-density moose populations in winter. Studies conducted in the GYA portion of the Intermountain West accent the variability of moose habitat use. The results generally fit into one of Peek?s (1974b) five categories, but there are important differences in habitat use by moose in this area and the moose of other areas. For example, McDowell and Moy (1942) did a descriptive study of moose habitat use in the Hellroaring/Slough Creek area north of Yellowstone National Park (Peek?s Type 5). They noticed an early winter association of moose and the limited willow areas, and then a move to adjacent conifer types, presumably in response to increasing snow depths. Harry (1957) and Houston (1968) documented use by moose of the extensive willow areas on the flood plains of Jackson Hole, Wyoming (Peek?s Type 2). Stevens (1970) found Douglas fir and aspen communities to be the key winter range in the Gallatin Mountains (Peek?s Type 3). Tyers (unpublished data, Tyers and Irby 1995) investigated moose habitat use on Yellowstone?s northern range and documented moose using older lodgepole pine forests during the most difficult winter months where they browsed almost exclusively on subalpine fir saplings and seedlings (Peek?s Type 5). HUMAN ACTIVITIES There are few examples in the literature that describe the effect of various types of human activity on wintering moose. Although several studies address changes in movements and habitat use, none appear to demonstrate resulting demographic changes. Moose are thought to be comparatively tolerant of humans and to have the ability to develop a high level of habituation (Shank 1979). This is illustrated in several ways, including flight distance. Moose unaccustomed to humans usually run about 150 yards, but habituated individuals may allow approaches to within 20 to 25 yards (Shank 1979). As a further example, Westworth et al. (1989) found that moose in British Columbia were able to habituate to disturbances associated with surface mining, including vehicular traffic, plant machinery, and blasting of ore reserves. Pellet group densities, used as an index of moose abundance, were highest on a transect 100 yards from the open pit. This transect had a particularly high density of browse leading the authors to concluded that moose distribution was influenced more by browse availability among different habitat types than by disturbance associated with mining. Pellet groups also demonstrated moose activity as close as 15 yards from the pit at sites where browse was present. The response of moose to the mine in British Columbia (Westworth et al. 1989) and similar situations may be explained by a theory proposed by Geist (1971). He stated that if visual and acoustical stimuli are predictable in space and time, the process of habituation by wildlife is enhanced. Mine activity and some forms of winter recreation can be predictable. In contrast, panic responses may occur as a result of any kind of abrupt unexpected intrusion (Busnel 1978). Westworth et al. (1989) proposed that the mine was actually an asset to moose. Moose in the area are exposed to predation by wolves. The mining activity displaced wolves, offering security to moose not available away from the mine site. Rudd and Irwin (1985) investigated impacts to wintering moose resulting from oil and gas extraction and recreational activities in western Wyoming. The number of shrub species available in proximity to a plowed road was the best predictor of moose presence or absence. Relative to people on snowshoes, skis, or snowmobiles, trucks associated with resource extraction caused the greatest disturbance to moose. People on snowshoes or skis caused more disturbances than snowmobiles. The average distance 18 moose ran to escape trucks was 16.9 yards, and the average distance at which moose where displaced was 169 yards; 21 percent were displaced, and 48 percent showed some type of disturbance behavior. The average distance 19 moose moved away from people on snowshoes or skis was 16.6 yards, and the average distance at which moose were displaced was 80.7 yards; 17 of the 19 moose moved to a different location, and all showed signs of disturbance. The average distance 242 moose ran to escape a snowmobile was 10.5 yards, and the average distance at which moose were displaced by snowmobiles was 59.25 yards; 50 percent of the encounters between moose and snowmobiles resulted in displacement while 94 percent showed some form of disturbance. Rudd and Irwin (1985) recommended that winter recreational use and mine activity be restricted near preferred moose winter range. Ferguson and Keith (1983) addressed the influence of nordic skiing on moose and elk in Elk Island National Park, Alberta. They found that cross-country skiing influenced the general over-winter distribution of moose. Moose tended to move away from areas near heavily used trails more than lightly used trails during the ski season (January through March). Daily movements away from trails occurred after the onset of skiing. However, once displacement occurred, additional skiers did not generate a greater displacement. The flight behavior of moose is unusual and often misinterpreted. Their reputation of being tolerant to humans may in part be because their stress response is more subtle than that of other ungulates. Shank (1979) reported a common response of moose to a disturbance was that they rarely reacted immediately and overtly to disturbing stimuli unless that stimulus was very intense. Often, they continued feeding and might even increase the intensity of feeding. While this is occurring, they moved without obvious sign of stress toward cover. Once cover was reached, they usually looked directly at the source of the disturbance, often for the first time, and then ran. Until the moose bolts, stress may not be obvious because it is expressed in less noticeable physiological responses, such as increased breathing and elimination rates. Reports dealing specifically with collisions between wintering moose and vehicles and trains are more common. Examples can be found from most areas with important moose populations. Because winter recreation frequently involves plowing roads and accessing recreation areas with motorized conveyance, the topic is relevant. Lavsund and Sandegren (1991) reviewed moose/vehicle relations in Sweden and described the situation as a serious problem both in terms of human safety and mortality of moose. Risk was highest at dawn and dusk and higher at night than during the daytime. In southern Sweden where winter snow accumulation is less important, collisions peak in early summer during calving and in autumn during the rut. In northern Sweden, collisions peak during December and January when snows initiate moose migrations to lowland ranges where major roads are common. Various methods were tried to reduce the number of moose/vehicle collisions. Repellants in the form of flashing lights, sounds, and scents were not effective. The results of roadside clearing to improve visibility for drivers demonstrated a reduction that was no better than what might have been arrived at by chance. Efforts to educate drivers on how to scan the roadside and anticipate risks did not seem to change driver behavior?good drivers were cautious, and bad drivers remained incautious. Neither road authorities nor drivers were interested in reducing the speed limit. Fencing the roads was effective at reducing collisions by 80 percent. In Alaska, measures were taken to mitigate moose/vehicle collisions along a stretch of highway that was improved (Child et al. 1991). A moose-proof fence, moose underpass, and highway lighting all were effective at significantly reducing collisions. Collisions were reduced 95 percent in the fenced portion of the highway when compared to the previous decade before the highway was improved and mitigation measures were put in place. The reduction in loss of moose allowed an increase in hunter harvest. Child et al. (1991) estimated that approximately 10 percent of the annual allowable harvest in the province of British Columbia die as a result of collisions on highways and railways. The impact of this on the demographics of the moose population is unknown. Collisions between moose and motorists on the Kenai Peninsula, Alaska, were also reported to be a severe problem (Del Frate and Sparker 1991). The number of road-killed moose nearly doubled following the new policy of the Department of Transportation to improve snow-clearing efforts. Better road conditions allowed motorists to travel faster. Collisions also increased during a severe winter when moose sought relief from harsh snow conditions by attempting to winter close to plowed roads. In response, a public awareness program was started using roadside signs, bumper stickers, and programs in schools. The number of moose mortalities declined 18 percent the following year, but the authors were not confident the education program was responsible. The results were confounded by mild winter conditions that allowed moose to winter farther from the roads. As mitigation, they called for avoiding building roads in moose winter range, brushing roadsides to increase visibility, and fencing. Rudd and Irwin (1985) found that site features had some effect on how moose tried to escape humans. When exiting roads freely, moose selected areas with less steep slopes than random samples, especially slopes of less than 5 percent. In 83 percent of the cases, moose exited at points where snow depth along the road was less than the average depth, although this difference was not statistically significant. During forced exits, moose chose slopes in proportion to what was available. The average snow depth of the berm was significantly greater along the road than where moose exited under duress. The average canopy closure was significantly greater at these exit spots than in random samples. Bubenik (1997) reported that mature, healthy moose stand their ground when confronted by wolves, and inexperienced moose generally run and are killed. Child et al. (1991) and Bubenik (1997) saw a connection between this and the high incidence of collisions with trains. Moose use the same survival strategy during confrontations with trains as they do with wolves. With trains this tactic is fatal. The problem is exacerbated by the effect of headlights, which hypnotize moose and interfere with avoidance movements. Anderson et al. (1991) determined that snow conditions greatly influenced annual variation in moose killed by trains in Norway. Mean annual snow depth was able to explain 84 percent of the annual variation in train kills. They believed three factors were responsible for this close correlation. First, early snows seemed to increase the speed, timing, and magnitude of moose movements to winter range. This places them on train tracks earlier in the season. Secondly, although moose are morphologically adapted for survival in snow, snow depths of greater that 39 inches seemed to motivate moose to seek the plowed railroad beds for movements between feeding sites. Third, as snow depths increased moose were less successful at escaping the tracks in the face of oncoming trains. Because of snow conditions they returned to solid ground on the tracks and tried to outdistance the approaching train instead of climbing over the snow berm. In addition, more collisions occurred after dark when moose were more active; they became hypnotized by train lights and train personnel had greater difficulty observing moose. They also found temperatures below 20? C tended to increase the risk of collision, while temperatures above 0? C had the opposite effect. The authors speculated this occurred because moose are foraging more actively at lower temperatures. Becker and Grauvogel (1991) investigated moose/train collisions in Alaska. They observed that most moose that were struck were using the tracks as a travel corridor in a winter environment. Most had time to exit the tracks but, instead, usually tried to outrun the train. Snow depths were around 35.5 inches, and moose that did leave the tracks floundered and returned to the tracks, which probably increased their sense of vulnerability to a perceived predator, the train. They experimented with decreasing the average speed of the trains (from 48 to 25 miles per hour) to see if moose mortalities could be reduced. The reasoning was that at a reduced speed there would be more reaction time for train personnel and more time for moose to escape. The reduction did not reduce the number of moose mortalities, and the train company determined that, based on economics, they could not afford to reduce the train?s speed below 25 miles per hour. The authors believed that a threshold did exist below which a positive response would occur, but it appears to be below 25 miles per hour, which is not economically practical for the train company. Modafferi (1991) also investigated the relationships between moose/train collisions, snowpack depth, and moose distribution. The setting was the lower Sustina Valley in Alaska. More than 73 percent of mortalities occurred from January through March. Mortality was greatest along stretches of railway that passed through moose winter range. As snow depth increased, mortalities increased. POTENTIAL EFFECTS The literature indicates moose can be impacted by human activities in the winter. However, moose habitat requirements are specific, and their use of selected areas is traditional. The presence or absence of moose winter activity is easy to verify through tracks, pellet groups, beds, sightings, and evidence of browsing. Investigations in summer or winter will demonstrate whether or not moose are using the area as winter range. As discussed, the specific attributes of moose winter range are variable. However, in all cases a winter range will include a concentration of accessible browse material such as deciduous trees and shrubs, especially willow and aspen. In some cases, browse may be subalpine fir saplings. Cover, in the form of dense coniferous forests, may also be present. Some of the best moose winter range is found where browse concentrations are in juxtaposition with cover. If snow conditions preclude access to the browse, moose will not be present. Impacts of recreational use may take several forms. Moose may be negatively impacted by a loss of winter habitat if construction of facilities removes habitat features resulting in a loss of foraging opportunities or cover. Negative impacts may also occur if moose are subject to displacement that results in a drain on energy reserves. Because they are often in an environment where snow is deep, flight can be energetically costly. The literature indicates flight and stress are most likely when the source of the disturbance is unpredictable, is severe to sensory perception, and is in close proximity. There is also the possibility that if disturbances are not of this nature, moose may habituate to human activities and show high tolerance. Moose may even seek centers of human activity as security from predators. Moose are also uniquely vulnerable to mortality by collisions with vehicles. This is because of the relationship between moose, browse availability, and snow conditions. Plowed roads or train tracks in moose winter range offer moose relief from snow conditions as well as travel corridors to sources of browse. This, combined with their instinctive response of standing their ground in the face of a perceived threat help explain why this is such a serious problem in many areas. Winters with above average snow depths exacerbate the problem. Text continued on website

Keywords: animal, mammal, ungulate, moose , Alces alces, human activity, habitat, behavior, migration, population, mortality, Greater Yellowstone Ecosystem, Yellowstone National Park, Jackson Hole, Teton County, Predation, Canidae, Canis lupus, Wolf, Wildlife, Management, Hunting, Carnivore, Ursidae, Bear, Food, Foraging, Breeding, bibliography