Traveling Fast and Silent: Mountain Biking With Grizzly Bears

The impacts of mountain bikers on wildlands and wildlife is at the center of a heated nation-wide debate fueled by increasing numbers of increasingly well-organized bikers intent on gaining access to backcountry areas. There is no better example of the contentious debate between mountain bikers and wilderness advocates than in deliberations over how to manage remaining roadless areas on the Custer-Gallatin National Forest in Montana. Proponents of mountain-biking feature rights and equity in a rhetoric that unambiguously places ego front and center. Opponents feature moral imperatives to protect intrinsic values as well as irreplaceable wildlands for future generations.

Debates such as this one arising from fundamentally different ethical stances—even visceral impulses—are rarely resolved through the invocation of evidence. Under such circumstances most people selectively promote or disregard information in service of ideological purposes. Even so, I remain incurably optimistic about the prospects for empiricism.

Given these premises, what follows is a summary of what is known or can be readily deduced about both the impacts of mountain bikers on grizzly bears as well as the impacts of mountain bikers on themselves through hazards that inevitably arise from moving silently and at high speeds in areas occupied by grizzlies. I’ve restricted my focus to grizzly bears because they are an animal I am familiar with. Beyond that I know just enough to be dangerous. What I present here is extracted from a report I recently produced in which I review research on relations between grizzlies and people on foot (i.e., pedestrians) and within which you can find relevant citations and references for what follows.

The Hazards of Mountain Biking

Mountain bikers occupy a conceptual middle-ground between pedestrians and people on or in motorized transport. They do not employ noisy mechanized equipment that potentially gives advance warning of their progress, but at the same time they move at potentially high speeds. Unlike people enclosed in hard-sided mechanized vehicles, but like people riding off-road-vehicles (OHV) or on foot, they are exposed to the risks of physical injury from an attacking grizzly bear. Given these provisos, mountain bikers qualify for extrapolation of research that is otherwise focused on pedestrians, primarily because of their comparative silence as well as vulnerability.

Emblematic of this point, Brad Treat was killed by a grizzly bear in Montana during June of 2016 after essentially colliding with the bear while he was traveling at high speed on a mountain bike along a trail with limited visibility. This incident elevated the profile of risks for both people and bears posed by mountain biking, although a number of similar incidents in Canada had highlighted the hazards of mountain biking as much as 20 years earlier. Concern about risks have also been magnified by the fact that mountain biking is becoming more popular in areas occupied by grizzly bears, reflective of the 28% increase nationwide in this activity during the last 10 years.

The few scientific investigations of encounters between bikers and grizzly bears paint a stark picture. Data pooled from all of the available reports show that 87% of all documented encounters were at distances less than 50 m, and that 52% involved females with young. Of these close encounters, 89% resulted in the biker either being approached or charged by the involved bear. Not surprisingly, of the 41 encounters described by bicyclists interviewed by Matt Schmor in Alberta, bears were described as being “startled” during 66% of them.

These risk-related figures are far in excess of the averages for other encounters between pedestrians and grizzly bears. The percent of encounters that elicited some kind of aggressive response from involved bears is an astounding 14-times greater for mountain bikers compared to for people on foot. Even if, compared to pedestrians, a greater number of “encounters” went undetected by mountain bikers, this alone would not account for the magnitude of this disparity. Moreover, the obvious heightened reactivity of bears to mountain bikers is not surprising given that average encounter distances were closer for bikers compared to the average 70-90 m involving pedestrians—and well within the overt reaction distance recorded for most grizzly bears.

These results are not unexpected. As Jake and Steve Herrero noted nearly 20 years ago, mountain biking is a perfect recipe for hazardous close encounters with grizzly bears given that bikers are often traveling silently at comparatively high speeds (11-30 km per hour), which increases the odds of rapid closure prior to detection, along with amplified reactivity among even highly tolerant bears. This same point has subsequently been made in several assessments of hazards posed by mountain biking in grizzly bear habitat.

The disproportionately large number of encounters between mountain bikers and female grizzly bears with young is also not surprising. If a person is approaching at high speed, solitary bears are plausibly better able to detect the approach and leave before being seen. By contrast, females with young are predictably challenged and delayed by marshaling their offspring before being able to depart, even if they detect an oncoming bicyclist at a distance. The plausible outcome is an encounter at close range with a highly reactive female grizzly bear mobilized in defense of her young.

And, Then, Impacts on Bears

The flip side of this dynamic between mountain bikers and grizzly bears is the likely short- and long-term impacts on involved bears. Greater immediate reactivity on the part of bears almost certainly translates into more rapid and sustained subsequent flight, along with longer-term energetic and physiological costs associated with impaired foraging, increased movements, and displacement of activity to sub-optimal times of day.

Moreover, if an encounter has turned out tragically for the involved human, the involved bear will likely pay for the outcome with its life, as was apparently intended when numerous well-armed men expended considerable effort to find the grizzly that killed Brad Treat after a surprise collision.

Mountain Biking is Hazardous for People and Detrimental to Bears

The weight of evidence unambiguously supports concluding that mountain biking is far more hazardous for involved people and more impactful on affected bears compared to any other pedestrian activity with the exception of hunting. Given this perhaps self-evident verdict, it is not surprising that Parks Canada seasonally or permanently closed trails to mountain bikers several years ago in areas where chances of hazardous encounters were high (the Minnewonka, Moraine Lake Highline, and Bryant Creek trails).

Returning to where I started, I am under no illusion that this recitation of evidence and well-supported inferences will settle debates over whether mountain bikers should have increased access to roadless wildlands. If nothing else, those who view recreating on bikes as an entitlement would probably insist that potential harm to animals such as grizzly bears be proven beyond any reasonable doubt—as opposed to being well-supported by the weight of evidence, as in this essay. In the end, evidence is judged in reference to ethical propositions that inescapably reflect the kinds of people we want to be and the kind of world we want to leave our grandchildren.

David Mattson worked for the grizzly study team for 2 decades. He retired from the US Geological Survey two years ago.