People often visit U.S. national parks to catch a glimpse of wildlife. But how does our presence impact the animals we hope to see?

National park traffic has grown steadily over the past decade, and popular parks like Yosemite and Yellowstone can easily see over a million visitors a year. In these heavily used areas, one might expect animals to change their behavior to avoid humans.

But a new 91̽��-led study has found that even in remote, rarely visited national parks, the presence of even just a few humans impacts the activity of wildlife that live there. Nearly any level of human activity in a protected area like a national park can alter the behavior of animals there, the study found. The was published Oct. 13 in the journal People and Nature.

“There’s been increasing recognition of how much just the presence of humans in these places, and our recreating there, can impact wildlife,” said senior author , associate professor in the 91̽��School of Environmental and Forest Sciences. “These results are striking in showing that really any level of human activity can have an effect on wildlife.”

The research team based its study in Glacier Bay National Park, a coastal area in southeast Alaska that is accessible only by boat or plane. Most visitors arrive on cruise ships, but the boats don’t dock on shore, and the park has very little human foot traffic. Because so few people visit each year — only about 40,000 but increasing — the park was an ideal place to locate this study, Prugh explained.

“Glacier Bay is a great park to explore what the lower limits are where humans start to affect wildlife behavior,” Prugh said.

The researchers worked with the national park’s staff to design and implement an experiment that compared wildlife activity in areas used frequently by humans to areas where people were absent. They installed 40 motion-activated cameras across 10 sites to capture detections of people and four animal species — wolves, black bears, brown bears and moose — over two summers. By controlling where and when people could access certain areas of Glacier Bay and then measuring wildlife responses to the differing levels of human activity, the researchers identified two important thresholds.

First, if humans were present in an area, the cameras detected fewer than five animals per week across all four species studied. In most cases, this likely meant that animals avoided areas where humans were present. Second, in backcountry areas, wildlife detections dropped to zero each week once outdoor recreation levels reached the equivalent of about 40 visitors per week.

The researchers were surprised by the apparent low tolerance wildlife had for the presence of people nearby.

“It was eye-opening to see the number of wildlife sightings we are ‘missing’ just by recreating in backcountry areas of Glacier Bay,” said lead author , who completed this work as a 91̽��graduate student. “I was surprised that for all four species, wildlife detections were always highest when there wasn’t any human activity. So many people visit national parks for the chance to view wildlife, and that desire alone may reduce the chance of it happening.”

Though all four species showed some change in activity due to humans, wolves were most likely to disappear from cameras when people were around. Brown bears were the least impacted by human presence. Moose, however, were more active during the times of day and locations where people were seen. The researchers hypothesize that moose might be using humans as a protective shield from predators, opting to align their active hours with humans to avoid becoming prey.

The researchers expect that in parks where animals are more accustomed to seeing people, at least some individual animals won’t react as strongly to humans as in Glacier Bay. But the findings do shed light on a reality that’s likely playing out at national parks and wilderness areas across the country: More people are visiting these areas than ever before, and the presence of humans is almost certainly impacting the behavior of animals that live there.

“I expect that similar results could be found in other national parks, particularly those with relatively low visitation. I wouldn’t be surprised if more and more people seek out less popular national parks to explore, which will have interesting and important implications for park management and wildlife,” Sytsma said.

National parks and wilderness areas aren’t just seeing more visitors during the high season. More people are opting to use the trail systems during less-busy times to avoid crowds. Additionally, some parks are expanding their trail networks to accommodate more visitors.

The authors hope this study can help park managers consider different approaches to making parks accessible both to humans and animals. For example, managers could consider concentrating trails and human use in certain areas to reduce their total footprint, or put restrictions on the time of year or days in which people can visit.

“Our findings lend support to concentrating human activities in some areas, because if you’re going to go above zero human activity and it’s going to have an impact, you might as well go way above zero in some areas and then have other areas where you have almost no human activity,” Prugh said. “In those areas, then, wildlife can live their natural lives unaffected by people.”

Co-authors are at the 91̽��and at Glacier Bay National Park and Preserve. This research was funded by the National Park Service.

For more information, contact Prugh at lprugh@uw.edu and Sytsma at mirasytsma@gmail.com.

For humans, the early days of the COVID-19 pandemic were a stressful time, marked by fear, isolation, canceled plans and uncertainty. But for birds that inhabit developed areas of the Pacific Northwest, the reduction in noise and commotion from pandemic lockdowns may have allowed them to use a wider range of habitats in cities.

A new 91̽�� led by reports that many birds were just as likely to be found in highly developed urban areas as they were in less-developed green spaces during the peak of the COVID-19 lockdowns. The paper was published Aug. 11 in the journal Scientific Reports.

“Our findings suggest that some birds may have been able to use more spaces in cities because our human footprint was a little lighter,” said Sanderfoot, who completed the study as a doctoral researcher in the 91̽��School of Environmental and Forest Sciences and is now a postdoctoral scholar in the Department of Ecology and Evolutionary Biology at the University of California, Los Angeles.

“For about half of the species we observed, neither land use nor canopy cover had an effect on their site use. That’s very interesting, because we would expect that whether a habitat was mostly covered in concrete or vegetation would tell you something about what birds would be there,” Sanderfoot said.

In the spring of 2020, Sanderfoot and colleagues recruited more than 900 community scientists in the Pacific Northwest to participate in the study. The volunteers chose their own monitoring sites — mostly backyards and parks where they could safely comply with public health orders — and recorded the birds they observed over a 10-minute period at least once a week. This community science approach allowed the researchers to gather data despite the lockdowns and gave many volunteers a welcomed distraction from the stresses of the pandemic.

“I am loving being a part of this!” said Nadine Santo Pietro, a study volunteer, in a written comment as part of the project. “I signed up to observe once a week for 10 minutes but it has become so much more than that. … I am learning so much! And it’s given me something positive to focus on during this strange time we are in right now.”

Volunteer Elaine Chuang wrote: “Being involved not only as a survey participant, but also as a mentor gives me a role in bringing greater appreciation of birds and nature in general to the community at large.”

Among the 35 species that showed the strongest changes in behavior were some of the Pacific Northwest’s most iconic, including black-capped chickadees, great blue herons, downy woodpeckers and Wilson’s warblers. The researchers focused on 46 bird species overall, which were observed by the study volunteers during more than 6,000 individual surveys.

In order to compare the volunteers’ bird observations to human activity, Sanderfoot and her colleagues used data from Google’s Community Mobility Reports, which track the relative amount that people moved around at various points during the pandemic. While most people spent spring of 2020 isolated in their homes, many began venturing out again over the course of the study period.

As people returned to public spaces and human activity increased, the study volunteers recorded an increase in sightings of several bird species. Because they were mostly monitoring in parks and backyards, which tend to be more heavily vegetated, provide more canopy cover and offer more resources for birds than other areas in cities, this could indicate that these green spaces are an important refuge for urban birds.

“The birds may have been elsewhere at the height of the lockdowns, because human activity wasn’t as much of a disturbance, but then returned to those vegetated areas as the activity increased again,” Sanderfoot said. “This could tell us how important it is to build green spaces into our cities. That’s the biggest takeaway for me.”

Other co-authors are , a professor in the 91̽��Department of Environmental and Occupational Health Sciences, and , an associate professor in the 91̽��School of Environmental and Forest Sciences.

This research was funded by the National Science Foundation Graduate Research Fellowship Program and the McIntire-Stennis Cooperative Forestry Research Program from the USDA National Institute of Food and Agriculture.

For more information, contact Sanderfoot at osanderfoot@g.ucla.edu, Kaufman at joelk@uw.edu and Gardner at bg43@uw.edu.

Press release written by Will Shenton, 91̽��College of the Environment.

As smoky air becomes more common during Washington’s wildfire season, many wildlife enthusiasts wonder: What happens to the birds?

Few studies have looked at wildfire smoke impacts on animals, let alone birds. And as Washington and the larger West Coast continue to experience more massive wildfires and smoke-filled air, understanding how birds are affected by smoke — and how air pollution may influence our ability to detect birds — are important factors for bird conservation.

Researchers from the 91̽�� now provide a first look at the probability of observing common birds as air pollution worsens during wildfire seasons. They found that smoke affected the ability to detect more than a third of the bird species studied in Washington state over a four-year period. Sometimes smoke made it harder to observe birds, while other species were actually easier to detect when smoke was present. The June 29 in the journal Ornithological Applications.

“We want to know how wildfire smoke affects birds and other wildlife, and this study is a great place to start,” said lead author , a doctoral candidate in the 91̽��School of Environmental and Forest Sciences. “Smoke clearly has an impact on detection of wildlife, and that hasn’t been adequately explored in the literature to date. Now we know that smoke pollution specifically affects our observations of birds and our ability to detect them.”

The researchers combined data from , an online citizen-science program managed by the Cornell Lab of Ornithology, with publicly available data from an extensive network of air quality monitors across Washington state. They were able to analyze how fine particulate matter, known as PM2.5 and a marker of smoke pollution, affected the probability of observing 71 common bird species during the wildfire seasons of 2015 to 2018. Higher concentrations of smoke affected the chances of observing 37%, or 26, of the bird species included in the study.

Sixteen of the bird species were harder to observe with more wildfire smoke, the study found. These include turkey vultures, Canada geese, two gull species, bald eagles and several other birds of prey. Many of these birds are observed circling high above the ground, so it’s not surprising that people would have a harder time detecting them on smoky days, the authors said. However, 10 additional species were easier to observe when smoke concentrations were higher. These include three types of warblers, cedar waxwing, spotted towhee and California quail.

The reasons for this aren’t clear and are outside of the scope of this study, but the authors lay out some hypotheses for future exploration. It could be that reduced visibility due to smoke pushes some birds lower to the ground where they can be more easily seen and heard. Or, as smoke prompts birds of prey to relocate, that could alleviate pressure on some songbirds and cause them to be more active — and thus more detectable by people.

“These behavioral changes are all hypotheticals, and we very much hope that researchers follow up on them because we have a lot to learn about how smoke affects wildlife,” Sanderfoot said.

Conservation and management efforts rely on the ability to observe animals in the wild, and it’s no different for birds. Air pollution clearly plays a role in detecting animals, and this paper makes the case that it should be considered alongside other factors like time of day, temperature and precipitation that all can influence observations of animals.

“If we see or hear birds more or less frequently because of smoke, that also impacts bigger inferences we make in terms of how certain bird populations are doing,” said senior author , an associate professor in the School of Environmental and Forest Sciences. “We want to get that part right, so we first need to understand the effect of air pollution on how we’re seeing birds in the wild.”

The researchers chose a four-year study period that included some summers where wildfire smoke was heavy in parts of the state, and other summers where smoke was negligible. All of the species included in the study had to have had at least 750 observations recorded for the first year (2015), and all observations used were within about 20 miles (32 kilometers) of an air quality monitor in Washington.

Data from the catastrophic 2020 wildfire season was not part of this analysis, although air quality during that period was worse than in any of the years in the study. As extreme wildfire seasons like 2020 become more common, it’s important to consider the influence of events like these in future studies, the researchers said.

This research was funded by the National Science Foundation and the McIntire-Stennis Cooperative Forestry Research Program from the USDA National Institute of Food and Agriculture.

For more information, contact Sanderfoot at oliviavs@uw.edu and Gardner at bg43@uw.edu.