New Haven, Conn. — A new large-scale study led by a research team from the Yale Center for Biodiversity and Global Change has found that wildlife responds not only to how humans reshape their habitats, but also to the simple presence of humans — and sometimes in surprising ways.
Even small changes in how people move through environments can significantly affect animal behavior and could have implications for wildlife conservation efforts, the study finds.
"Our findings provide an important nuance in our understanding of wildlife in a rapidly changing world," said Walter Jetz, a professor of ecology and evolutionary biology in Yale's Faculty of Arts and Sciences and director of the Yale Center for Biodiversity and Global Change.
"Animals are affected by both direct human presence and by human-caused changes to the physical environment, such as agriculture and urbanization," Jetz said. "This study is the first to directly assess at scale how both causes, separately and in combination, impact wildlife habitat usage."
The study, published in Science , culminates a six-year, global collaboration between Yale researchers and colleagues from more than 5o academic and governmental organizations across the U.S. and abroad.
The study was led by Ruth Oliver, formerly a postdoctoral scientist in Yale's Department of Ecology & Evolutionary Biology who is now an assistant professor at the University of California Santa Barbara's Bren School of Environmental Science and Management; and Scott Yanco, another former Yale postdoctoral associate who is now a research ecologist at the Smithsonian's National Zoo and Conservation Biology Institute.
The study's overall findings suggest that to protect wildlife, conservationists should consider not just habitat loss, but also where and when people are physically present.
In their work, researchers used GPS devices to track 37 species (22 birds and 15 mammals) across the United States. Mammal species included white-tailed deer, wolves, coyotes, raccoons, skunks, and some of the "big cat" species. The birds included large species such as vultures, hawks, ducks, crane, and storks.
In all, researchers collected about 11.8 million location points from more than 4,500 animals.
For the first time ever, the team then used mobile phone data, paired with satellite-derived measurements of human habitat disturbance, to study how both aspects of human behavior affected animal movement and habitat use.
"It has been challenging to capture the impact of human presence on wildlife," said Oliver. "Mobile device data are typically not available, but our study was made possible thanks to a unique partnership that made estimates of human presence available to researchers during the COVID-19 pandemic."
COVID-19 lockdowns dramatically altered human movement patterns, allowing researchers to study differences in human presence between 2019 and 2020. This enabled researchers to separate the effects of human presence on animal behavior from longer-term landscape changes such as urban development and agriculture.
The researchers measured the space that animals used and the variety of habitats they occupied and then applied statistical models to link these behaviors to human activity and environmental conditions.
Results showed that more than 65% of species changed their behavior based on the presence of humans, and that this human presence tended to matter most in less-developed, natural settings. But different species responded in different ways. Many reduced the amount of space they used, probably to avoid people, but others had the opposite response.
Gray wolves, for example, expanded their range, possibly traveling farther to steer clear of humans. Ravens also covered more ground, likely taking advantage of food sources linked to people, while coyotes tended to restrict their movements.
The study also found that individual animals could adjust their behavior from year to year, demonstrating some flexibility in response to changing human activity.
"Habitat loss is the key driver of biodiversity loss, but as we show, human's direct use of the landscape — say for recreation — also mediates this effect," Jetz said. "Depending on the quality of remaining habitat, animals make behavioral adjustments that either amplify or dampen the negative effects of habitat loss."
The study highlights how new technologies, such as GPS tracking combined with satellite data and measures of human presence, can uncover new insights into how wildlife responds to humans.
The findings also suggest that in addition to habitat preservation, efforts to skillfully manage the timing and intensity of human activity — such as limiting traffic during key periods or reducing disturbance in sensitive habitats — may help wildlife and people coexist.
"The cutting-edge technology used in this study allows us to see, with unprecedented detail, how variable wildlife responses to human activities really are," Yanco said. "This means that conservation strategies need to be very targeted, not one-size-fits-all."
