03271nas a2200241 4500008004100000245008700041210006900128300001200197490000700209520250600216653002502722653001902747653002602766653002602792653003502818653002702853100002202880700001602902700001902918700001702937700002002954856005502974 2011 eng d00aQuantifying the Sensitivity of Camera Traps: An Adapted Distance Sampling Approach0 aQuantifying the Sensitivity of Camera Traps An Adapted Distance  a464-4760 v273 a

1. Abundance estimation is a pervasive goal in ecology. The rate of detection by motion-sensitive camera traps can, in principle, provide information on the abundance of many species of terrestrial vertebrates that are otherwise difficult to survey. The random encounter model (REM, Rowcliffe et al. 2008) provides a means estimating abundance from camera trap rate but requires camera sensitivity to be quantified.

2. Here, we develop a method to estimate the area effectively monitored by cameras, which is one of the most important codeterminants of detection rate. Our method borrows from distance sampling theory, applying detection function models to data on the position (distance and angle relative to the camera) where the animals are first detected. Testing the reliability of this approach through simulation, we find that bias depends on the effective detection angle assumed but was generally low at less than 5% for realistic angles typical of camera traps.

3. We adapted standard detection functions to allow for the possibility of smaller animals passing beneath the field of view close to the camera, resulting in reduced detection probability within that zone. Using a further simulation to test this approach, we find that detection distance can be estimated with little or no bias if detection probability is certain for at least some distance from the camera.

4. Applying this method to a 1-year camera trapping data set from Barro Colorado Island, Panama, we show that effective detection distance is related strongly positively to species body mass and weakly negatively to species average speed of movement. There was also a strong seasonal effect, with shorter detection distance during the wet season. Effective detection angle is related more weakly to species body mass, and again strongly to season, with a wider angle in the wet season.

5. This method represents an important step towards practical application of the REM, including abundance estimation for relatively small (<1 kg) species.

10aabundance estimation10aanimal density10acamera detection zone10adetection probability10apassive infrared motion sensor10aRandom Encounter Model1 aRowcliffe, J., M.1 aCarbone, C.1 aJansen, P., A.1 aKays, R., W.1 aKranstauber, B. uhttp://dx.doi.org/10.1111/j.2041-210X.2011.00094.x