PS 11-96 - On-trail or off-trail- Camera trap placement for evaluating species characteristics

Background/Question/Methods

Reliable estimation of species richness, abundance, activity and subsequent monitoring are important in achieving specific conservation goals through evidence-based management. However, selection of suitable techniques requires a-priori assessment of their accuracy, precision, replicability, and cost-effectiveness before the technique is recommended on a large scale. Camera traps (CT) have been widely used as a wildlife monitoring tool due to their objectivity and ability to generate information on a large spectrum of species. Information from them is used for inferences on myriad characteristics of species and is commonly used to address management decisions on a large scale all over the world. A basic assumption of all inferences from CT studies is that the data generated are unbiased representation of underlying parameters. However, the most common CT study, the capture-recapture model designed to maximize detections of the target species (primarily large carnivores) is essentially non-random and often not systematic. Such CT designs also generate secondary data that are commonly used to infer information about non-target species, which can lead to bias due to differential use of trails by different species. Attempts to evaluate if such designs result in a biased inference and of what magnitude have been few

Results/Conclusions

Herein we simultaneously generate and compare estimates obtained from camera traps (a) placed to optimize large carnivore captures and (b) random placement, to infer accuracy and biases for parameter estimates. Both setups recorded 25 species when same number of trail and random cameras (n = 31) were compared. However, species accumulation rate was faster with trail cameras. Relative abundance indices (RAI) from random cameras surrogated abundance estimated from capture-mark-recapture and distance sampling, while RAI were biased higher for carnivores from trail cameras. Group size of wild-ungulates obtained from both camera setups were comparable. Random cameras detected nocturnal activities of wild ungulates in contrast to mostly diurnal activities observed from trail cameras. Our results show that trail and random camera setup give similar estimates of species richness and group size, but differ for estimates of relative abundance and activity patterns. Therefore, inferences made from each of these camera trap designs on the above parameters need to be viewed within this context.