Non-pregnant females showed no interest in being near roads.
But the distance between roads and the birthing sites used by pregnant moose shrank by about 410 feet (125 meters) a year.
An expanding bear population in the region is probably the main driver behind this steady movement toward areas of high human activity, Berger said.
In areas without bears, the moose moms didn't seem to gravitate toward roads—supporting the idea that moose actively seek out human-built corridors as refuges from predation.
Grizzly bears have only recently moved back into the Grand Teton region, Berger noted. (related photos: survival of the grizzly bears.)
Over time, he predicts, the bears will become increasingly bold in pursuing moose into areas close to roads and the shield effect will diminish.
Observations from the past few years suggest the predators are starting to lose their fear.
"The bears are starting to figure this out," Berger said.
But the new finding contrasts with results from other locations.
Terry Bowyer, a biologist at Idaho State University in Pocatello, studied moose-bear interactions in Denali National Park in Alaska.
"Moose [in Denali] do not give birth near roads, and bears are not traffic-averse," Bowyer said.
Both he and study author Berger agree that the disparity is probably due to the Alaskan populations' more continuous association with humans, as well as with each other.
The new finding from the Grand Tetons is fascinating, Bowyer said.
"It illustrates how humans may influence predator-prey dynamics, something that previously had been underappreciated."
Berger added that national parks are often used to study species in a natural setting.
But animal behavior may be influenced in unexpected ways by the millions of visitors flooding the parks each year and the facilities built to accommodate people.
"We need to better understand the consequences of the infrastructure we put in place," Berger said.
"Just by being there we have changed the distributions and behavior of some species."
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