The presence of humans and human infrastructure in U.S. national parks has lasting effects on the behaviours of the large animals that call them home, according to a new study.

“Wildlife all around the world fear people and avoid areas of high human activity, but it was surprising to see that this holds true even in more remote protected areas,” said Dr. Kaitlyn Gaynor, a zoologist at the University of British Columbia and lead author of the paper published today in the Proceedings of the Royal Society B.

Researchers tracked 229 animals from 10 species across 14 national parks and protected areas using GPS collar data from 2019 to 2020, allowing them to study how animals navigated hotspots of human activity in parks before and during the COVID “Anthropause”. Species included grey wolves, mountain lions, black and grizzly bears, moose, mountain goats and bighorn sheep.

While overall, animals tended to avoid infrastructure such as roads, trails, parking lots, buildings and campgrounds, closer analysis showed responses varied across populations, species and individual animals. “This study reveals not only how wildlife respond to human presence but also why species respond differently, and the complex ways that animals balance risks and benefits associated with humans,” said co-author Dr. Forest Hayes, postdoctoral fellow at Colorado State University.

“Some species are just more wary of people than others, like bighorn sheep and mountain lions, while others have learned to associate humans with some benefit,” said Dr. Gaynor. “The mule deer and elk in Zion National Park prefer being closer to developed areas and around humans. That could be because their predators might be avoiding people, so if deer and elk can learn to live with us, they can reduce the risk of becoming prey.”

Avoidance even during lockdown

The researchers found animals in more developed areas switched from avoiding human infrastructure when the park was open in 2019 to using it more when the park was closed in 2020. Without any people around, animals were apparently more willing to explore the developed areas of the park.

“We heard from managers in Yosemite National Park that when people came back, the black bears stayed, which caused a lot of problems because the bears got used to the abundant food in Yosemite Valley and didn't want to give it up,” said Dr. Gaynor.

But in most other parks, avoidance of human infrastructure persisted even during the lockdowns. “While some individuals and populations showed a strong response to the absence of people during park shutdowns, most did not,” Dr. Gaynor said. “Because a lot of headlines in 2020 implied that animals were taking back our national parks and were on the streets everywhere, we expected to see a bigger effect. But it takes just a few individuals to start changing their behaviour to create the perception of a larger impact.”

The researchers speculate that due to the relatively short duration of park closures—an average of 58 days —many animals may not have had enough time to perceive and respond to the change in human activity, particularly those with low exposure to human development in their home ranges. Additionally, risk-averse individual animals and species may have already been displaced prior to the pandemic, while those animals with a high exposure to humans were already habituated.

Balancing recreation and conservation

Human presence influences both the resources available to animals and the risk of using those spaces, with differing effects on animal species. The responses of animals may shape which species eat and compete with each other, changing ecological dynamics, the researchers say. These responses may also affect the ability of animals to persist alongside people in protected areas.

U.S. national parks, which hosted over 327 million visits in 2019, balance the dual mandates of human recreation and wildlife conservation.

“Yellowstone National Park, Yosemite National Park and the Grand Canyon are international destinations that are crowded at peak times of year, but the crowds are concentrated near the roads and visitor centres and parking lots,” said Dr. Gaynor. “The study provides evidence that conservation is compatible with recreation at low levels but that we do need to keep some areas exclusively for wildlife.”

Journal

Proceedings of the Royal Society B Biological Sciences

DOI

10.1098/rspb.2025.1013

Wednesday, July 23, 2025

Yellowstone aspen showing signs of recovery following 1995 reintroduction of wolves to park

Yellowstone National Park is celebrating an ecological milestone along with a key anniversary this summer, Oregon State University researchers report.

A paper published today in Forest Ecology and Management documents the first new generation of overstory aspen trees in Yellowstone’s northern range in 80 years, three decades after wolves were reintroduced to the nation’s oldest national park.

Without predation pressure from wolves, which had been extirpated from the park by 1930, elk populations grew to the point that their browsing was thwarting the growth of young aspen. The ecosystem effects were widespread as aspen stands support a range of species including beavers and cavity-nesting birds.

With wolves back in the mix along with bears and cougars, a nearly extirpated predator whose numbers increased along with wolf reintroduction, elk numbers have been reduced and aspen are once again working toward becoming full-grown trees.

“The reintroduction of large carnivores has initiated a recovery process that had been shut down for decades,” said the study’s lead author, Luke Painter, who teaches ecology and conservation in the OSU College of Agricultural Sciences. “About a third of the 87 aspen stands we examined had large numbers of tall saplings throughout, a remarkable change from the 1990s when surveys found none at all.”

Another third of the surveyed stands had patches of tall saplings growing into new overstory trees, he added, and the rest remained suppressed by herbivory.

“Increasing numbers of bison may be emerging as a new constraint to aspen in some areas,” Painter said.

The fact that stands with many tall saplings have low rates of browsing, whereas other stands continue to be suppressed, indicates aspen recovery is happening because of a trophic cascade and not other factors such as climate or site productivity, he said.

In a trophic cascade, a change at the top of a food web causes ripple effects throughout an ecosystem, altering its structure and balance. In Yellowstone, top predators have reduced herbivory by elk, allowing aspen to begin to recover.

“This is a remarkable case of ecological restoration,” Painter said. “Wolf reintroduction is yielding long-term ecological changes contributing to increased biodiversity and habitat diversity.”

Collaborating with Painter were Robert Beschta and William Ripple of the OSU College of Forestry. The Ecosystem Restoration Research Fund of the Oregon State University Foundation supported the research.

Journal

Forest Ecology and Management

DOI

10.1016/j.foreco.2025.122941