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The Effects of Motorized Access on Wildlife in the Northern Rockies
The U.S. northern Rocky Mountains cover a huge area of relatively pristine and undeveloped land, creating unique areas of core habitat for many important carnivore and ungulate species. However, many parts of this region also have a long history of resource extraction and road building. On Forest Service lands alone, there are more than 50,000 miles of roads. Today many areas in this region are being rapidly developed and critical wildlife habitats are increasingly being fragmented. In this paper, I review recent studies regarding the effects of roads and motorized vehicle access on carnivores and ungulates in the northern Rocky Mountains. Numerous other studies, outside the geographic focus area, are not addressed.
Overall ecosystem effects of motorized vehicles and roads are well documented. Roads contribute to habitat fragmentation, decreased habitat effectiveness, interrupted migration and travel patterns, increased human-wildlife encounters, and increased direct mortality (Havlick, 2002). While roads are linear and fragmenting, they do offer some level of predictability for wildlife. Off-road vehicles (ORVs), however, travel on trails or cross-country on snow or open landscapes, and are not generally predictable. This further decreases habitat effectiveness, and creates additional opportunities for direct collision and negative human-animal encounters (Havlick, 2002).
ORV technology has advanced considerably in the last two decades, and machines can now travel much farther and faster than ever before. This obviously increases the ability of users to venture deeper into the mountains. As well, ORV ownership has skyrocketed in the last decade. As of 2003, there were approximately 36 million registered all-terrain vehicles (ATVs) and 12 million registered snowmobiles nationwide (Brininstool, 2006).
Heavily studied in the past two decades, grizzly bears show behavior modification and mortality effects from roads and vehicle use (For a more comprehensive review see the RIPorter 13.1). In a study examining habitat selection, road density and vehicle traffic effects on female grizzly bears in the Swan Mountains of northwest Montana, Mace et al. (1996) reported that habitat selection decreased in direct proportion to road density. During spring, when bears are most vulnerable and when vegetation availability increased at low elevations, bears selected habitat with an average density of 0.52 km/km2. In summer, when vehicle traffic counts were highest, bears again negatively selected for areas with a higher road density. Negative selection continued through the fall, when average road density for selected habitat was 0.34 km/km2. In addition, bears negatively selected for roads that had traffic counts of over 10 vehicles per day (Mace, et al. 1996).
A study in the Badger-Two Medicine area of the Lewis and Clark National Forest in Montana found that bears selected against a 200-900m zone surrounding ATV trails and selected against a 400-650m zone surrounding single-track trails with some motorbike use (Graves, 2002).
Wolves have also been extensively studied in the northern Rockies. Most importantly for wolves is the direct correlation between mortality and roads. In a study on wolf dispersal from Glacier National Park, 21 of 25 dispersing wolves were killed by humans (15 shot, 4 poisoned, 2 trapped), and they were killed within 200m of a road or seismic line (Boyd and Pletcher, 1999). Whittington, et al. (2005) reported unpublished Parks Canada data that 43 wolves had been killed by vehicle collisions from 1994-2004 in Jasper National Park.
While studies in the Midwest suggest a 1mi/mi2 threshold for wolf persistence, wolves in the Rocky Mountains will often utilize habitat with higher road densities than in the Midwest (Claar, et al. 1999). Numerous studies from both the Midwest and the Rocky Mountains point out that wolves will generally select areas of higher road density when there is low human presence and select areas of lower road density as human presence increases (Fuller, et al. 1992; Whittington, et al. 2005; Boyd-Heger, 1997).
Few studies address the effects of motorized vehicles on lynx in the northern Rockies, however, two recent studies report confounding results. A 2004 study in the Uinta Mountains of northeast Utah discovered that coyotes do utilize compacted snow trails caused by snowmobiles to access deep snow habitat preferred by lynx. The authors showed that 70-80% of coyote tracks were located in areas that had snowmobile trails present over 60% of the time (Bunnell, et al. 2004).
A 2007 study, however, reported little interspecies competition between lynx and coyotes. Conducted in the Seeley Lake area, a popular snowmobile destination in northwest Montana, researchers concluded that although coyotes did use compacted snowmobile trails more than expected, it was unlikely that the trails strongly affected interspecies competition (Kolbe, et al. 2007).
There is a limited amount of data regarding wolverines and motor vehicles; however, there are comprehensive habitat and mortality studies that can be used to extrapolate vehicle effects on wolverines. A study of wolverine habitat use in central Idaho found that wolverines generally prefer high elevation habitats throughout the year and in areas with high roadless percentage (81% roadless in study area), they did not select negatively against roads (Copeland, et al. 2007).
A study in British Columbia concluded that female wolverines negatively selected for habitat in areas that had helicopter and backcountry skiing and for areas that had been logged while positively selecting for roadless areas (Krebs, et al. 2007). A study in Montana concluded that trapping is a significant source of mortality for wolverines. Of the 14 known mortalities during the study period (2001-2005) nine were from trapping. Roads and trails allow access for trappers and thus act as a significant impediment to wolverine population viability (Squires, et al. 2007).
Nearly all the scientific literature agrees that increased road densities result in decreased elk populations (for further review, see Rowland, et al. 2003). In a seminal study, Lyon (1983) stated that at road densities of 1 mi/mi2 effective elk habitat was reduced by 25%. At road densities of 2 mi/mi2 effective habitat decreased by 50%, and at road densities of 6 mi/mi2 elk use of suitable habitat declined by 75%. Other studies corroborate a decrease in elk populations, success of elk hunting, and increased poaching as road densities increase (Gratson and Whitman, 2000; Canfield, et al. 1999).
Perhaps the most informative study on elk and ORVs was conducted in the Starkey Experimental Forest in northeast Oregon. Wisdom et al. (2004) subjected the elk to a series of disturbances by all terrain vehicles (ATVs), mountain bikes, horseback riders and hikers in a controlled experiment. Probability of elk flight response for ATV, mountain bike and hiking disturbances was 0.65 when the disturbance was at close range (under 500m), and 0.55 for horseback riders. Beyond 500m, probability declined for hiking and horseback riding, but remained high for ATV and mountain biking until distance increased to 1500m. Additionally, elk moved more when subjected to ATV and mountain bike activity than horseback or hiking (Wisdom, et al. 2004).
A Yellowstone National Park study reported generally minimal behavior response by elk to over-the-snow activity in the park. However, the authors acknowledged that behavioral responses varied depending on number of participants, number of animals in a group, location of animals (meadow, forest, geothermal habitats), and interaction times (White, et al. 2005). Additionally, some studies indicate that elk non-behavioral responses to snowmobiles in Yellowstone National Park are significant. A 2002 study reported that fecal glucocorticoid levels (a measure of stress) paralleled snowmobile activity and were higher for snowmobiles than for wheeled vehicles (Creel, et al. 2002).
Motor vehicles affect wildlife on both an ecosystem and individual scale throughout the northern Rocky Mountains of the U.S. While additional research is needed to examine the particular effects on specific species and populations, almost all scientific evidence points to increased habitat fragmentation, decreased habitat suitability, direct mortality effects, and increased flight response across species and habitats. As motor vehicles, particularly off-road vehicles, continue to penetrate areas of historically secure habitat, wildlife will continue to feel negative effects.
Greg Peters is a University of Montana Environmental Studies graduate student and currently an intern with Wildlands CPR. He initially conducted an assessment on this topic for American Wildlands.
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