Tracking 4,581 Animals Shows Human Presence Alone Changes Wildlife Behaviour

Researchers from the University of California, Santa Barbara, the Smithsonian's National Zoo and Conservation Biology Institute, and Yale University have found that wild animals respond not only to the landscapes humans build but also to the simple fact that people are physically nearby. The study, published in the journal Science, combined GPS tracking data from 4,581 individual mammals and birds spanning 37 species with anonymized cellphone location data collected across the continental United States.

The researchers compared animal movement during matching periods in 2019 and during the 2020 COVID-19 lockdowns, when restrictions dramatically altered where and how people moved, a period the team calls the "anthropause." This let them separate the effect of human presence from the effect of permanent landscape changes such as roads, farms and cities. The team said this marked the first time anonymized cellphone geolocation data had been used this way to study wildlife.

Overall, 57% of the species studied were affected by both human presence and landscape modification together. Human presence alone was linked to a change in the territory or habitat range used by 67% of the mammal species and 68% of the bird species studied. About 67% of mammal species and 41% of bird species reduced the habitat they used when people were both present and the landscape was altered. The effect was strongest in places with relatively little development, such as national parks, compared with cities.

Responses varied widely by species. Wolves expanded their habitat use around humans, which researchers said may reflect their long history of avoiding people. White-tailed deer's habitat use grew as landscapes became more modified but shrank as human presence increased, while sandhill cranes showed the opposite pattern. Study co-lead Ruth Oliver, of UC Santa Barbara's Bren School, said the findings highlight the need for conservation strategies tailored to individual species rather than a single general approach.