In areas with high levels of human activity, mammal movements can be reduced by as much as three-fold, a new study reports. Restricted movement holds implications not only for the individual animals affected, but also for whole ecosystems if ecological interactions and the distribution of nutrients are also altered. Currently 50 to 70% of the land on Earth is modified by human activities. To better understand the impact of these alterations, Marlee A. Tucker et al. analyzed a GPS-tracking database of 803 individual organisms across 57 species, comparing their movements to the Human Footprint Index (HFI). The HFI captures multiple indicators of human activity, including the extent of built environments, cropland, pasture land, human population density, nighttime lights, railways, roads, and navigable waterways. The researchers found that, on average, mammal movement was about 6.6 kilometers in areas with a high human footprint, compared to 21.5 kilometers in areas with a low human footprint. Of note, reduced movement was particularly evident when animals were tracked for longer periods of time, suggesting that humans are altering animals' ranging behavior and area use over longer time scales, rather than altering their travel speeds. The researchers used modeling to explore whether individuals alter their movements relative to the human footprint, or whether certain species that exhibit long-range movement simply do not enter areas of high human activity; their results suggest that both factors play a role. In addition to the human footprint effect, body mass, dietary guild, and resource availability were also related to movement distances, the authors report.