Scientists have discovered that human presence significantly influences where and how wildlife moves and lives, sometimes with effects as strong as those of roads, cities, and other human-made structures. In a new study published in the journal Science, researchers tracked the movements of 4,581 individual mammals and birds across the continental U.S. during matching periods in 2019 and 2020. They combined GPS tracking data from 37 animal species with anonymized cellphone geolocation data to explore how human activity affects wildlife behavior. This is the first time such data have been used in this kind of research. The study found that different species respond to human presence in varying ways, and these responses also depend on how much a landscape has already been altered by human activity. For instance, 57% of the species studied were affected by both human presence and landscape changes. Human presence influenced the amount of territory or the size of the environmental niche for 67% of mammal species and 68% of bird species. These effects were often connected — the impact of people on an animal was partly determined by how much the landscape had already been modified, and vice versa. In some cases, animals reduced the amount of habitat they used in response to human presence and landscape changes. This was true for about 67% of mammal species and 41% of bird species. Interestingly, animals were more sensitive to human presence in areas with less development, like national parks, compared to highly urbanized areas. For example, wolves expanded their habitat use in response to humans, possibly due to their complex historical relationship with people. In contrast, white-tailed deer expanded their environmental niche as landscapes became more modified but reduced it when human presence increased. Sandhill cranes showed the opposite pattern. The study is part of the COVID-19 Bio-Logging Initiative, an international effort to understand how wildlife responded to the drastic changes in human activity during the pandemic. Researchers called this period the "anthropause," a time when human movement was significantly reduced. Earlier findings from the initiative showed widespread behavioral changes in mammals, shifts in marine traffic, and the importance of directly measuring human movement when studying wildlife. The initiative involved 600 partners and collected over 1 billion location records from about 13,000 animals to better understand human-wildlife interactions. The new findings highlight how combining GPS tracking data with mobile-device data can lead to more precise conservation strategies, helping scientists distinguish between the effects of human infrastructure and the effects of people simply being present. Researchers are now exploring how human-driven changes to landscapes and climate affect animal survival, a question that was previously difficult to study in detail.