In 2026, scientists tracked 4,581 animals across 37 species; more than 65% changed their behaviour simply when humans were nearby

For decades, scientists studying how humans affect wildlife have focused largely on what people build — roads, cities, farms and other changes to natural habitats. But a new study suggests that the physical presence of people itself can change animal behaviour. Researchers tracking 4,581 mammals and birds across 37 species found that more than 65% of the species changed how they used space when humans were nearby.

The finding was particularly striking in relatively undeveloped areas, where animals often appeared more sensitive to people than those living around heavily developed landscapes. It suggests that even when humans have not permanently changed a habitat, simply being there can influence how wildlife moves and uses its surroundings.

The study, published in Science, was conducted by researchers from the University of California, Santa Barbara, the Smithsonian’s National Zoo and Conservation Biology Institute, and Yale University. The team combined animal GPS tracking with anonymised cellphone location data to separate the effects of human presence from permanent landscape changes.

COVID lockdowns created a rare wildlife experiment

Normally, it is difficult to tell whether an animal is responding to people themselves or to the roads, buildings and other development surrounding them. The COVID-19 lockdowns provided researchers with an unusual opportunity because human movement changed sharply while the physical landscape remained largely the same.

The researchers compared weekly GPS records from 4,581 individual mammals and birds during matching periods in 2019 and 2020. They then used anonymised cellphone location data with neighbourhood-level resolution to determine where people were present.

According to the researchers, this was the first time such cellphone data had been used to directly examine how human presence affects animal movement.

“Typically, private companies hold onto these, which made this a rare opportunity for us to quantify how human presence impacts wildlife,” said Scott Yanco, a research ecologist at the Smithsonian’s National Zoo and co-lead author.

Animals did not respond to people in one universal way

Human presence was associated with changes in the territory or environmental niche used by 67% of mammal species and 68% of bird species. Overall, 57% of the species were affected by both human presence and landscape modification.

The response also depended on how heavily an area had already been altered. Animals in relatively undeveloped places, including national parks, were particularly sensitive to people compared with wildlife in heavily developed areas.

The study found that about 67% of mammal species and 41% of bird species reduced the amount of habitat they used when human presence and landscape changes were considered together.

Wolves, deer and cranes showed opposite reactions

The researchers found major differences between species.

Wolves, for example, expanded their habitat use when humans were present. This may reflect their tendency to move farther away from people or spread out to avoid human activity.

White-tailed deer showed a different pattern. Their environmental niches expanded as landscapes became more modified but contracted as human presence increased. Sandhill cranes displayed the opposite response.

Ruth Oliver, an assistant professor at UCSB’s Bren School of Environmental Science & Management and co-lead author, said these differences make species-specific conservation important.

“Every species has different habitat requirements, has its own particular behavioral tendencies and faces unique threats. Effective conservation requires that we understand the particular challenges that each species faces.”

Scientists now want to know if the changes are harmful

The research is part of the COVID-19 Bio-Logging Initiative, which studied wildlife responses during the pandemic’s “anthropause”. The wider project involved about 600 partners and collected roughly 1 billion location records from nearly 13,000 animals.

The new study shows that protecting habitat alone may not fully capture the impact of humans. Conservation plans could also need to consider where and when people enter sensitive wildlife areas.

Researchers are now investigating whether behavioural changes caused by human activity help animals adapt or indicate stress.

“Our current study shows that animals change how they use space and resources, but we don't know if these changes are helping them adapt or are a sign of stress,” Oliver said.

The researchers believe the findings could eventually support more targeted policies, including decisions about recreational access and when wildlife needs greater distance from people.