Humans have a pervasive influence on ecosystems across the world, with well-documented effects on animal behavior and ecology. Animals frequently avoid areas of high human activity, perceiving risk not only from direct harassment and hunting but also non-lethal activities and infrastructure. In places where humans and animals coexist, animals may exhibit temporal avoidance of humans, shifting their activities to avoid overlap with humans in time rather than space. In particular, recent studies suggest many large mammal species may be shifting their activities toward nocturnal hours. The extent to which these shifts are occurring globally is currently unknown. To examine anthropogenic effects on large mammal diel activity patterns, we conducted a meta-analysis using telemetry, camera trap, and observational data from 100 case studies across gradients of human disturbance. For each study, we calculated the effect of human disturbance on nocturnality, using response ratio as a measure of effect size. We then built generalized linear models to examine the effect of taxon, habitat, disturbance type, study design, and other factors on the strength and direction of the effect size.
Results/Conclusions
Our global study reveals strong evidence that humans are creating a more nocturnal world as animals shift activity to the nighttime. Animals are significantly more likely to exhibit nocturnal (vs. diurnal) activity in areas of high human disturbance compared to areas of low disturbance. Changes in the timing of animal movement, foraging, and habitat use are consistent across continents, habitats, taxa, and types of human activity. Such responses can result in dramatic shifts away from natural diurnal patterns, with effects on foraging and hunting efficiency, predator and competitor detection, and social behavior that may affect individual fitness and population persistence. Temporal community dynamics may also change as species exhibit differential responses to humans, altering patterns of competition, predation, and herbivory. However, shifts in activity pattern may represent adaptive temporal niche partitioning that allows for humans and wildlife to share the same space. As the human footprint expands across the globe, temporal avoidance of humans can reduce human-wildlife contact and potentially conflict.