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© R. Bear Stands Last- All Rights Reserved

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Roads to Trouble

Killing Wilderness and Bears

“Roads probably pose the most imminent threat to grizzly habitat today…The management of roads is the most powerful tool available to balance the needs of bears and all other wildlife with the activities of humans…Any un-roaded land represents important and unique opportunities…Management should seek to maintain these areas as un-roaded wherever possible.” - US Fish and Wildlife Service, Grizzly Bear Recovery Plan, 1993

Over the last decades, experts have documented the harmful effects of roads and motorized vehicle use on grizzly bears, other wildlife, and their wildland ecosystems. Of particular concern is road-building and unregulated all-terrain vehicle (ATV) use on public lands, including the only habitats remaining for wildland-dependent species, such as grizzlies.  Some effects of roads can be mitigated, as with highway under or over passes, while others cannot. With too many roads and too little wilderness, grizzly bears likely wink out.


Historically, grizzly bear managers have focused on managing logging roads and related use but, due to technological improvements which allow vehicles to penetrate further into the most remote country, use has escalated to extraordinary levels.


Ironically, the mighty grizzly bear is more sensitive to roads and human development than most other wildlife species, so protecting the grizzly bear protects other species as well.


Using different methodologies, studies in Yellowstone and the South Fork of the Flathead have pointed to the need for road densities below 1 mile/square mile in order for female grizzly bears to survive.  Refining this analysis to account for variations in landscape and forest cover, researchers in Yellowstone found that road densities should be as low as 0.26 miles/square mile.

Some key findings


Grizzly Bears:  Grizzlies are displaced from areas with roads and motor-vehicle activity, which in turn increases the likelihood of conflict with humans and the probability of human-caused mortality.


  • Bears avoid areas of human activity, development and roads by as much as 4 km, regardless of the level of human activity.

  • Roads and vehicle use fragment critical bear habitat, shrinking habitat into smaller secure pockets. This isolates populations and lowers genetic diversity.

  • A 1999 Study by the Interagency Grizzly Bear Study Team found that grizzly bear deaths in roaded areas is five times as likely as in non-roaded areas.  (Mattson et al. 1996)

  • In a 1989 Study, 63% of all know human-caused grizzly deaths were found to occur within 1 km of a road on Montana’s Rocky Mountain Front. Of the 11 bears killed near roads, 10 females.  (Aune & Kasworm 1989)

  • Using different methodologies, studies in Yellowstone and the South Fork of the Flathead have pointed to the need for road densities below 1 mile/square in order for female grizzly bears to survive. 

  • Refining this analysis to account for landscape variability and forest cover, researchers found that road densities should be as low as .26 miles/square miles in a flat, clear-cut area of the Targhee Forest. 


Bison, Elk and Other Big Game:  The availability of ungulate meat like bison and elk is an important factor in the survival of Yellowstone grizzly bears.  This meat accounts for almost half of the annual intake for females and more than 70% of the intake for males. Consider these facts.


  • Bison, elk and other big game are entirely displaced from an area when road densities reach 6 miles/square mile.

  • Vehicle use reduces elk habitat effectiveness by 25% where road/trail densities exceed 2 miles/square mile.

  • Roads and vehicle use fragment and reduce big game habitat, disrupt natural migratory patterns and isolate populations. 

  • Vehicle use leads to competition for resources, and an increase in stress levels and potential for illness.

  • Vehicle use impacts breeding habits, calf survival and the social order of herds.

  • Vehicle use results in a disproportionate loss of bull elk by facilitating access.


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