The inappropriate use of time-to-independence biases estimates of activity patterns of free-ranging mammals derived from camera traps

Measuring and comparing activity patterns provide key insights into the behavioral trade-offs that result in animal activity and their extrinsic and intrinsic drivers. Camera traps are a recently emerged source of data for sampling animal activity used to estimate activity patterns. However, nearly 70% of studies using such data to estimate activity patterns apply a time-to-independence data filter to discard appreciable periods of sampling effort. This treatment of activity as a discrete event emerged from the use of camera trap data to estimate animal abundances, but does not reflect the continuous nature of behavior, and may bias resulting estimates of activity patterns. We used a large, freely available camera trap dataset to test the effects of time to independence on the estimated activity of eight medium- to large-sized African mammals. We show that discarding data through the use of time-to-independence filters causes substantial losses in sample sizes and differences in the estimated activity of species. Activity patterns estimated for herbivore species were more affected by the application of time-to-independence data filters than carnivores, this extending to estimates of potential interactions (activity overlap) between herbivore species. We hypothesize that this pattern could reflect the typically more abundant, social, and patch-specific foraging patterns of herbivores and suggest that this effect may bias estimates of predator-prey interactions. Activity estimates of rare species, with less data available, may be particularly vulnerable to loss of data through the application of time-to-independence data filters. We conclude that the application of time-to-independence data filters in camera trap-based estimates of activity patterns is not valid and should not be used.