Search

The random encounter model, a method for estimating animal density using camera traps without the need for individual recognition, has been developed over the past decade. A key assumption of this model is that cameras are placed randomly in relation to animal movements, requiring that cameras are not set only at sites thought to have high animal traffic. The aim of this study was to define a correction factor that allows the random encounter model to be applied in photo-trapping surveys in which cameras are placed along tracks to maximize capture probability. Our hypothesis was that applying such a correction factor would compensate for the different rates at which lynxes use tracks and the surrounding area, and should thus improve the estimates obtained with the random encounter model. We tested this using data from a well-known Iberian lynx Lynx pardinus population. Firstly, we estimated Iberian lynx densities using a traditional camera-trapping design followed by spatially explicit capture–recapture analyses. We estimated the differential use rate for tracks vs the surrounding area using data from a lynx equipped with a GPS collar, and subsequently calculated the correction factor. As expected, the random encounter model overestimated densities by 378%. However, the application of the correction factor improved the estimate and reduced the error to 16%. Although there are limitations to the application of the correction factor, the corrected random encounter model shows potential for density estimation of species for which individual identification is not possible.

Over the last 20 years surveys of the population of the Iberian lynx Lynx pardinus in Doñana National Park and its surroundings in Spain have produced estimates of a total population of 50–60 in fragmented patches. The population was estimated to be 26 adults in 2002–2003. Use of camera trapping and other field methods during 2004–2008 allowed us to determine the abundance of the lynx and to estimate demographic statistics. Estimated annual abundance of adult and subadult lynxes averaged 38 individuals (range 35–43). Although the population exhibited a continuous distribution it was concentrated in three major areas, including Doñana National Park, with an average area occupied of 620 km2. Our results suggest that the Doñana Iberian lynx population now has a different structure from that in the 1990s and in particular a more continuous spatial distribution. These results indicate an improved, but not secure, scenario for the population. The continuous geographical distribution suggests the population is currently less vulnerable to extinction than 10 years ago. Conservation actions now need to focus outside Doñana National Park on the reconversion of pine plantations into original Mediterranean scrubland habitat, and the continuity and intensification of ongoing restocking with rabbits in fenced areas.