Human activity has transformed natural landscapes for centuries, but new research suggests that wildlife may react just as strongly to people themselves as to the environments humans build.

By combining animal tracking data with anonymised mobile-phone location records, scientists were able to separate the influence of human presence from the effects of roads, cities and other permanent changes to the landscape.

The study, published in Science, analysed movement data from 4,581 mammals and birds representing 37 species across the continental United States. Researchers compared matching periods in 2019 and 2020, when COVID-19 restrictions caused major changes in where and how people moved.

A Rare Natural Experiment

The pandemic created an unusual opportunity for scientists. Normally, it is difficult to measure human presence directly because detailed movement data are rarely publicly available. Earlier wildlife studies therefore often relied on indirect indicators such as urban development, farmland or whether lockdown rules were in place.

For this project, however, the researchers had access to anonymised cellphone geolocation data at neighbourhood level. They combined those records with weekly GPS information from tracked animals, allowing them to examine how wildlife responded when the number of people in an area changed without the landscape itself necessarily changing.

Scott Yanco, a research ecologist at the Smithsonian’s National Zoo and Conservation Biology Institute and co-lead author of the study, explained that the unusual availability of mobile-phone data during the pandemic allowed the team to measure human presence more directly than is normally possible. He noted that this helped reveal effects that would have been missed by looking only at habitat modification.

People Matter As Much As Places

The results showed that wildlife responses could not usually be explained by landscape change alone. Around 57% of the species studied were influenced by both human presence and human modification of the environment.

Human presence was associated with changes in either the amount of territory animals used or the size of their environmental niche in 67% of mammal species and 68% of bird species.

The two effects also interacted. In many cases, an animal’s response to people depended on how heavily the surrounding area had already been modified, while the effect of landscape change depended partly on how many people were present.

About 67% of mammal species and 41% of bird species reduced the amount of habitat they used in response to the combined influence of people and landscape alteration. Animals appeared especially sensitive to human presence in relatively undeveloped areas, including national parks, compared with heavily urbanised environments.

Different Species, Different Reactions

One of the clearest findings was that wildlife does not respond to humans in a single predictable way.

Wolves, for example, expanded their habitat use when people were present. The researchers suggested that this could reflect the species’ long history of conflict with humans, potentially causing wolves to spread out or travel farther in an attempt to avoid them.

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

Ruth Oliver, an assistant professor at UC Santa Barbara’s Bren School of Environmental Science & Management and co-lead author, explained that these contrasting reactions underline the need for conservation strategies designed around individual species rather than broad assumptions about wildlife behaviour. She stressed that every species has different habitat needs, behaviours and threats.

What The Findings Mean For Conservation

The study forms part of the international COVID-19 Bio-Logging Initiative, which examined how animals responded to the dramatic changes in human activity during the pandemic. The wider collaboration involved around 600 partners and assembled roughly one billion location records from approximately 13,000 animals.

The new findings suggest that conservation planning may need to consider not only permanent infrastructure but also when and where people are physically present. This could influence decisions about visitor access, protected areas and the timing of human activities in sensitive habitats.

However, the study does not show whether these behavioural changes are beneficial or harmful to wildlife. Animals may be adapting successfully, or their altered movements could reflect stress. Oliver said the research team is now investigating whether animals that change their behaviour in response to human pressures face a higher or lower risk of dying.

The research therefore adds an important layer to the way scientists understand human-wildlife interactions. Roads and cities clearly matter, but so does the simple presence of people — and different species can respond in dramatically different ways.