07/11/2026
Male grizzly bears in Yellowstone use the same hiking trails that tourists walk during the day. They just wait until dark.
A 2025 study published in the Journal of Wildlife Management by Loggers and colleagues examined 17 years of GPS collar data from grizzly bears in Yellowstone National Park and compared it against the locations of recreation trails and backcountry campsites. Male grizzlies showed pronounced trail use during crepuscular and nocturnal hours, the window between last light and first light when the trails are empty. They were not wandering near trails by accident. They were selecting them as travel corridors, using maintained paths as energy-efficient routes through steep terrain the same way hikers do, just on a different schedule.
The trails are easier to walk than the surrounding forest. A grizzly bear moving through a dense Yellowstone drainage at night can either push through deadfall, wade through streams, and climb loose slopes, or it can walk a packed-dirt trail that humans graded and cleared of obstacles. The bear takes the trail. It saves energy. It covers more ground. And it does it during the hours when the thing it wants to avoid, people, is asleep in a tent or back in a parking lot.
Yellowstone's annual visitation doubled between 1980 and 2015.
The bears watched that happen in real time and adjusted. The study found that in areas with unrestricted recreation, male bears had already shifted their trail use to avoid peak human hours. In restricted areas, bear management zones where the Park Service limits human access seasonally, the same males showed even more pronounced nocturnal trail use, suggesting they were more comfortable using trails openly when fewer people were around. The implication is that in unrestricted areas, the presence of hikers had already pushed male bears into a tighter nocturnal window. The bears had read the schedule and compressed their activity into the gap.
Neither s*x spent time near backcountry campsites. The bears used the trails between the campsites but avoided the campsites themselves. They were treating the trail network the way a commuter treats a highway system: useful for getting somewhere, not for stopping.
The female bears did something different, and stranger.
In restricted areas where human access was limited, females varied their trail use and movement rates much more than males. In unrestricted areas, where hikers were present during the day, females were more consistent. The researchers interpreted this as a security tradeoff, but not between bears and people. Between female bears and male bears.
Male grizzlies kill cubs. Infanticide by adult males is a documented cause of cub mortality across grizzly populations. A female with cubs needs to avoid large males more urgently than she needs to avoid hikers. In areas with steady human foot traffic, large males stay away. The trail becomes a buffer zone. The hikers do not know it, but their presence on the trail during the day is functioning as a shield that keeps aggressive males out of the drainage until nightfall. The female and her cubs can forage in relative safety during the hours when the hikers are present because the thing that would actually kill her cubs will not come near the trail until the people leave.
When recreation was experimentally reduced by 85 percent in one Banff study area in 2023, grizzly bear detections on those same trails increased by 185 percent. The bears were not gone. They had been there the entire time, waiting in the timber for the trail to clear. When it cleared earlier, they came out earlier.
A hiker walking a Yellowstone backcountry trail at two in the afternoon is walking a route that a grizzly bear walked at two in the morning. The same packed dirt. The same drainage. The same bends where the trail drops toward the creek. The bear knows the hiker's schedule better than the hiker knows the bear exists.
Source: Loggers et al. (2025), Journal of Wildlife Management / Loggers et al. (2024), Journal of Wildlife Management / The Wildlife Society / Interagency Grizzly Bear Study Team.