Summary of Key Conclusions (for a brief audio summary see this video)

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• Grizzly bears manifest greater reactivity to pedestrians in several different ways, including greater likelihood of both flight and aggression during encounters, greater likelihood of spatial and temporal displacement, and greater avoidance of areas and times of day frequented by pedestrians.

 

• As a tautology, grizzly bears that are less reactive are more tolerant, with tolerance arising from either habituation to the presence of pedestrians or the need to abide nearby people as a prerequisite for accessing food or security from other bears.

 

• Grizzly bears likely transfer tolerance for other bears to pedestrians, with tolerance for conspecifics most evident in high-density coastal bear populations. The greater the intraspecific tolerance, the less reactive bears are likely to be during encounters with people.

 

• Benign human activities that are highly predictable in time and space lessen the likelihood of surprise encounters and allow for the emergence of tolerance among bears, both of which predictably lessen reactivity by bears.

 

• High levels of tolerance for pedestrians are most evident in areas with high densities of bears together with pedestrians concentrated in specific locales at specific times of day. The classic example of this circumstance is where anglers or bear viewers are closely regulated while near coastal salmon spawning streams.

 

• Under such conditions, adolescent grizzly bears and females with cubs-of-the-year (COY) often concentrate near pedestrians as means of escaping intraspecific competition as well as hazards posed by potentially predatory adult males. Under these circumstances, pedestrians plausibly serve as a “shield” for more security-conscious or subordinate bears.

 

• In the absence of spatially and temporally highly-predictable activity typically associated with heavy pedestrian traffic, there is essentially no evidence that pedestrians serve as “shields.” This important proviso covers almost all of the backcountry of interior North America.

 

• All other circumstances aside, individual bears that are more tolerant of pedestrians are less likely to be displaced by or avoid people. Compared to intolerant bears, tolerant bears are also more likely to be efficient foragers when pedestrians are nearby (nearer than 50-100 m).

 

• Even so, there is ample evidence that grizzly bears in coastal regions are, in aggregate, displaced by pedestrians, most commonly to times of day that are suboptimal for foraging. Absent avoidance and high levels of tolerance, foraging efficiencies are also commonly impaired by the presence of pedestrians especially when within 150 m.

 

• In interior regions, grizzly bears react more strongly to encounters with pedestrians when they are “startled” or “surprised,” which more often happens at distances of less than 30 to 150 m, typically in areas with greater vegetation cover and the obscuring sound of running water. Strong reactions predominantly include flight (during roughly 70% of encounters), but also aggression (during roughly 4-6%). Human injury is likely to occur during only 3-6 out of every 1000 encounters.

 

• Grizzly bears are more likely to react strongly to encounters with pedestrians in open areas, including alpine areas and grasslands, as well as in areas heavily used by people. Both circumstances predictably increase the odds that involved bears will feel both threatened and surprised.

 

• Compared to other bears, females with COY are far more likely to react strongly to encounters with pedestrians, most notably by 4 to 7-times more often charging the involved people. This greater reactivity almost certainly arises from defense of vulnerable offspring.

 

• After encounters, grizzly bears in interior regions flee on average nearly 2 km, increase levels of activity for 24-72 hours afterward, shift activity towards nocturnal and crepuscular hours, and select for areas of greater cover, all of which entail predictable energetic costs.

 

• Grizzly bears avoid areas near backcountry trails by an average of 250 m and backcountry campsites by an average nearer 550 m, while additionally selecting for night-time hours when near backcountry pedestrian facilities, presumably to avoid day-time concentrated human activity.

 

• Grizzly bears also avoid areas seasonally closed to dispersed pedestrian activity during times of year when these areas are open to human use, with impacts compounded by decreased use of open areas and more marked avoidance of areas where pedestrian activity is concentrated.

 

• As an exception to what would otherwise be a rule, grizzly bears are attracted to areas where big game hunters provision bears with food in the form of remains from ungulate kills, but with resulting increased risks to hunters arising from surprise encounters and the contestation of carcasses with bears.

 

• Compared to other bears, females with COY tend to exhibit greater avoidance of heavily-used pedestrian facilities, whereas adolescent bears tend to more often seek out areas with more human activity presumably to find security from dominant adult bears and to more freely access food.

 

• Overall, displacement and avoidance are most consistently exhibited by grizzly bears in the form of increased activity during nocturnal and crepuscular hours and diminished activity during daylight hours when people are most active.

 

• Overall, females with COY are most impacted by the presence of pedestrians, with implications for human safety. The notable exception to what would otherwise be a rule is in areas with heavy, concentrated, and predictable pedestrian activity, where females can find refuge for their cubs near people from threats posed by predatory adult males.