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.