Wildcat population density on the Etna volcano, Italy: a comparison of density estimation methods

Abstract

The European wildcat is an elusive felid that is declining across its range. Sicily hosts a distinctive insular wildcat population, the conservation of which requires much better ecological knowledge than is currently available, particularly population density. We simultaneously used two noninvasive methods (camera-trapping and scat-collection) to estimate the population density of wildcats on the Etna volcano. We conducted genetic analyses to identify individuals and to detect potential hybridization with the domestic cat. We analyzed individual capture-histories from camera-trapping and scat-collection using the spatially explicit capture-recapture (SECR) model. Furthermore, we applied the random encounter model (REM), which does not require individual identification, to the camera-trapping data. We identified 14 wildcats from 70 photographic detections (6.48 detections/100 trap-days) obtained from 1080 camera-trapping days over 4 months, and we estimated to have identified all the individuals living in the study area (10.9 km(-2)). On the contrary, we identified 10 wildcats from 14 out of 39 scats collected from 391 km of transects walked. The estimated densities (individuals km(-2) +/- SE) were 0.32 +/- 0.1 (SECR camera-trapping), 1.36 +/- 0.73 (SECR scat-collection) and 0.39 +/- 0.03 (REM). The population density estimates obtained from SECR camera-trapping and REM overlapped, although we recommend care when applying the latter. The SECR scat-collection gave the highest population density (and less precise) estimates because of the low number of capture and recaptures; however, the population size estimated with this method matched the number of individuals photographed. The population density of the wildcat in Etna falls in the medium-high range of those reported in literature, highlighting the role of this ecosystem for the long-term conservation of the wildcat in Sicily. Camera-trapping is confirmed as a useful tool to assess the wildcat population density and, in this case, was complemented by the genetic analysis that confirmed individual identity.