Data from: Camera trap placement and the potential for bias due to trails and other features

Camera trapping has become an increasingly widespread tool for wildlife ecologists with large numbers of studies relying on photo capture rates or presence/absence information. It is increasingly clear that camera placement can directly impact this kind of data, yet these biases are poorly understood. We used a paired camera design to investigate the effect of small-scale habitat features on species richness estimates, and capture rate and detection probability of mammal species in the Shenandoah Valley of Virginia, USA. Cameras were deployed at either log features or on game trails with a paired camera at a nearby random location. Overall capture rates were significantly higher at trail and log cameras compared to their paired random cameras, and some species showed capture rate increases as high as 9.7 times greater at feature-based cameras. We recorded more species at both log (17) and trail features (15) than at their paired control sites (13 and 12 species, respectively) yet richness estimates were indistinguishable after 659 and 385 camera nights of survey effort, respectively, for log and trail features. We detected significant increases (ranging from 11-33%) in detection probability for 5 species resulting from the presence of game trails. Detection probability was also influenced by the presence of a log feature for six species. Bias was most pronounced for the three rodents investigated, where in all cases detection probability was substantially higher (24.9-38.2%) at log cameras. Our results indicate that small-scale factors, including the presence of game trails as well as other features, can have significant impacts on the frequency and probability of species detection when camera traps are employed. Significant biases may result if the presence and quality of these features are not documented and either incorporated into analytical procedures, or controlled for in study design