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The Impacts of Snowmobiling and Cross-Country Skiing on Ungulates
Across the United States, outdoor recreation continues to rise in popularity while wildlife habitat continues to shrink. These converging trends increase the potential for negative human-wildlife interactions and make it imperative that society recognize how recreation affects wildlife (Knight and Temple 1995). This article reviews the literature concerning the impacts of snowmobiling and cross-country skiing on ungulates, and comments on the limitations of this research.
Ungulates are hoofed mammals such as deer, elk, bison, and moose. Although it is important to know how humans affect these animals throughout the year, the harsh, limiting conditions of winter make this a particularly vulnerable season for ungulates. As a result, wildlife biologists commonly recognize that winter recreationists potentially have a greater impact than their warm season counterparts (McCool 1978). During the winter, ungulates may be more susceptible to disturbance, which causes an increase in energy expenditure. Disturbances can elevate heart rate, increase vigilance, displace animals from their habitat, and can be detrimental if prolonged or repeated (Canfield et al. 1999).
Scientific studies find that both snowmobiling and cross-country skiing disturb ungulates, however, which form of recreation has a greater impact is still a source of controversy. Furthermore, most studies use different methods to measure the impacts of winter recreation, resulting in conflicting conclusions. Here is a brief review of the literature.
Several studies have examined the impacts of snowmobilers on ungulates. Bollinger et al. (1972) found that deer did not change their home range, or the area of land over which they moved, as a result of snowmobile activity. He did report though, that deer movements increased when snowmobiles were present. Dorrance et al. (1975) concluded that deer moved away from snowmobile trails during periods of snowmobile use, and that, at a test site with historically low snowmobile use, deer home ranges increased as a result of snowmobile activity.
A 1978 study by Richens and Lavigne reported that while snowmobiles did not îcause [deer] to [permanently] abandon preferred bedding and feeding sights," the deer did flee when snowmobiles approached. They even concluded that snowmobiles used in a judicious manner to create trails --- by compacting snow --- would benefit deer by facilitating movement to new sources of forage. Studying reindeer, Tyler (1991) found that flight response from snowmobiles consumed 0.4% of the reindeerøs daily energy expenditure. He concluded that, with one snowmobile disturbance per day, the reindeer were not adversely affected. However, Moen et al. (1982) found that deer heart rates increased in response to snowmobile provocation, raising energy expenditures without necessarily changing behavior.
Creel et al. (2001) compared fecal glucocorticoid levels in elk and wolves with snowmobile activity. He and his colleagues found that elk stress hormone levels rose and fell daily corresponding to the amount of snowmobile traffic. They also found that these levels were higher during snowmobile season than during the off season. For wolves, they reported that fecal glucocorticoid levels were substantially higher in an area with diffuse snowmobile traffic compared to an area where snowmobiles were not permitted.
Literature on the impacts of cross country skiing is much more limited. Ferguson and Keith (1982) were the first to publish a study on the effects of cross-country skiing on the distribution of moose and elk. They found that both moose and elk moved away from ski trails when the trails were in use. Further, they concluded that cross-country skiing influenced moose distribution during the winter, with moose being less likely to reside in areas used by cross-country skiers. Cassirer et al. (1992) reported that when people walked or skied directly towards elk, the elk were temporarily displaced, but returned shortly after people left the area.
Limitations of the Research
A direct comparison of the impacts of snowmobiles and cross-country skiers has been addressed in only two published studies (Freddy et al. 1986; Hardy 2001). Both studies found that cross-country skiers have a greater immediate impact because they are less predictable, and therefore more startling. Other studies have also found predictability to be a major factor in animal response to disturbance (Vaske et al. 1995). However, no studies compare the impacts of cross-country skiers and snowmobilers using the same predictable trails. Nor have any studies observed ungulate response to snowmobiles and crosscountry skiers both traveling in unpredictable locations. Additionally, no studies have considered the difference in noise produced by the two types of recreation, or the difference in distances travelled by motorized and non-motorized recreationists. Snowmobiles produce 73 decibels recorded from 50 feet, a level similar to a busy city street (WWA 2001; Smith 2002). A carefully controlled study is needed to establish the effects of noise.
A major limitation of published research on the impacts of snowmobiles is a failure to consider changes in snowmobile technology over the last few years. Modern snowmobiles have more power and can exceed speeds of 100 mph, but the studies cited here restricted speeds to 15 mph (Freddy et al. 1986; Tyler 1991). In addition, the power of new snowmobiles allows them to traverse terrain not previously possible, and to enter wildlands that were once devoidof any human disturbance during the winter months. This combination of speed and range has revolutionized access to remote habitat, and with it the potential for disturbance to wildlife.
Another gap in the research is in snowmobilesø impacts to vegetation. Both vegetation trampling and mortality and have been well documented (e.g. Wanek and Potter 1974), but no study has measured if a decrease in forage could impact ungulate populations.
Finally, the published studies lack data on the long-term impacts of recreation. While short-term studies measuring the immediate response of individual ungulates are easier to accomplish, they do not address how accumulated exposure affects a population over several seasons.
While the scientific literature is inconclusive, a snowmobileøs ability to cover large distances into remote areas, as well as the reach of its noise, may imply that snowmobiles have a greater impact on ungulates than previously understood. These concerns combined with snowmobilesø other environmental impacts may be of more consequence than the finding that when cross-country skiers are in unpredictable locations, they can have a greater impact than snowmobiles in predictable locations.
Research has shown, however, that both groups have the potential to negatively affect ungulates; therefore our primary concern should be on cumulative detrimental impacts. Although none of the published studies have proven that either type of recreation influences ungulates at the population level, Creel et al. (2002) and Hardy (2001) have presented evidence that individuals are feeling stress from wintertime recreation. The cumulative effects of this stress may someday lead to a reduction in ungulate populations.
It would be wise to take steps now to manage recreation access and educate recreationists about the impacts of their behavior. A good management strategy would restrict recreation to established, and therefore, predictable trails. Limiting the extensive range of snowmobiles may also be a good mitigation strategy, and keeping trails out of critical ungulate habitat areas is essential. Educational measures should focus on teaching recreationists not to seek close encounters with wildlife, and how to act so as to decrease ungulate disturbance.
--- Teresa Elise Welsh is a graduate student in Environmental Studies at the University of Montana.
Bollinger, J. G., O. J. Rongstad, A. Soom, and T. Larson. 1972. Snowmobile noise effects on wildlife. Final Report. University of Wisconsin-Madison.
Canfield, J. E., L. J. Lyon, J. M. Hillis, and M. J. Thompson. 1999. Ungulates. Chapter 6 in Effects of Recreation on Rocky Mountain Wildlife: A Review for Montana, coordinated by G. Joslin and H. Youmans. Committee on Effects of Recreation on Wildlife, Montana Chapter of The Wildlife Society.
Cassirer, E. F., D. J. Freddy, and E. D. Ables. 1992. Elk responses to disturbance by cross-country skiers in Yellowstone National Park. Wildlife Society Bulletin 20:375-381.
Creel, S., J. E. Fox, A. R. Hardy, J. Sands, B. Garrot, and R. O. Peterson. 2002. Snowmobile activity and glucocorticoid stress responses in wolves and elk. Conservation Biology 16(3):809-14.
Dorrance, M. J., P. J. Savage, and D. E. Huff. 1975. Effects of snowmobiles on white-tailed deer. Journal of Wildlife Management 39(3):563-69.
Ferguson, M. A. D., and L. B. Keith. 1982. Influence of Nordic skiing on distribution of moose and elk in Elk Island National Park, Alberta. Canadian Field-Naturalist 96(1):69-72.
Freddy, D. J., W. M. Bronaugh, and M. C. Fowler. 1986. Responses of mule deer to disturbance by persons afoot and snowmobiles. Wildlife Society Bulletin 14:63-68.
Hardy, A. R. 2001. Bison and elk responses to winter recreation in Yellowstone National Park. Masterøs thesis, Montana State University. Knight, R. L., and S. A. Temple. 1995. Wildlife and recreationists: coexistence through management. Chap 20 in Wildlife and Recreationists: Coexistence Through Management and Research, edited by R. L. Knight, and K. J. Gutzwiller. Washington D.C.: Island Press.
McCool, S. F. 1978. Snowmobiles, animals, and man: Interactions and management issues. Transactions of the North American Wildlife Conference 43:140-48.
Moen, A. N., S. Whittemore, and B. Buxton. 1982. Effects of disturbance by snowmobiles on heart rate of captive white-tailed deer. New York Fish and Game Journal 29(2):176-83.
Richens V. B., and G. R. Lavigne. 1987. Response of white-tailed deer to snowmobiles and snowmobile trails in Maine. Canadian Field-Naturalist 92(4):334-43.
Smith, S. 2002. The snowmobile lobbyøs snow job. Earth Island Journal. Summer: 13.
Tyler, N. J. C. 1991. Short-term behavioural responses of svalbard reindeer Rangifer tarandus platyrhynchus to direct provocation by a snowmobile. Biological Conservation 56: 179-94.
Vaske, J. J., D. J. Decker, and M. J. Manfredo. 1995. Wildlife management: An integrated framework for coexistence. Chap 3 in Wildlife and Recreationists: Coexistence through Management and Research, edited by R. L. Knight, and K. J. Gutzwiller. Washington D.C.: Island Press.
Wanek, W. E. and D. Potter. 1974. A continuing study of the ecological impact of snowmobiling in northern Minnesota (final research report for 1973-1974). The Center for Environmental Studies, Bemidji State College, Bemidji, Minnesota. 53pp.
Winter Wildlands Alliance. 2001. Losing ground: The fight to preserve winter solitude. 13 November. Available at http://ww.winterwildlands.org