Journal of Mammalogy, 94(1):73–81, 2013 Density estimations of the Eurasian lynx (Lynx lynx) in the Swiss Alps ELIAS PESENTI AND FRIDOLIN ZIMMERMANN* Department of Ecology and Evolution, University of Lausanne, Dorigny, CH-1015 Lausanne, Switzerland (EP) KORA, Thunstrasse 31, CH-3074 Muri, Switzerland (EP, FZ) * Correspondent: f.zimmermann@kora.ch Use of photographic capture–recapture analyses to estimate abundance of species with distinctive natural marks has become an important tool for monitoring rare or cryptic species, or both. Two different methods are available to estimate density: nonspatial capture–recapture models where the trap polygon is buffered with the half or full mean maximum distance moved by animals captured at more than 1 trap (1/2 MMDM or MMDM, respectively); or spatial capture–recapture (SCR) models that explicitly incorporate movement into the model. We used data from radiotracked Eurasian lynx (Lynx lynx) in the northwestern Swiss Alps (NWSA) during a low (1.0 lynx/100 km 2 ) and a high (1.9–2.1 lynx/100 km 2 ) lynx population density to test if lynx space use was density dependent. Second, we compared lynx density estimates resulting from these 2 different methods using camera-trapping data collected during winters 2007–2008 and 2009–2010 in the NWSA. Our results indicated lynx space use was negatively correlated with density. Lynx density estimates in all habitats using MMDM (0.86 and 0.97 lynx/100 km 2 in winters 2007–2008 and 2009–2010, respectively) were significantly lower than SCR model estimates, whereas there was no significant difference between SCR model (1.47 and 1.38) and 1/2 MMDM (1.37 and 1.51) density estimates. In the NWSA, which currently harbors the most abundant lynx population in Switzerland, 1/2 MMDM and SCR models provided more realistic lynx density estimates compared to the MMDM, which lies in the lower range of densities. Overall, the SCR model is preferable because it considers animal movements explicitly and is not biased by an informal estimation of the effective sampling area. Key words: camera-trapping, density, half mean maximum distance moved (1/2 MMDM), Lynx lynx, mean maximum distance moved (MMDM), spatial capture–recapture (SCR), Switzerland, telemetry Ó 2013 American Society of Mammalogists DOI: 10.1644/11-MAMM-A-322.1 In human-dominated landscapes, large carnivores often conflict with livestock breeders and hunters (Karanth et al. 1999; Meriggi and Lovari 1996) and their conservation thus depends on sound management (Fergus 1991; Trevers and Karanth 2003). Wildlife conservation and management require precise data regarding size, density, and structure of the focal populations and their trends over time. Total counts of most organisms, especially nocturnal, forest-dwelling species occur- ring at low densities are difficult to establish (Cederlund et al. 1998). However, if each individual in a population can be identified by distinctive natural marks, we can estimate capture probabilities and abundance by means of photographic capture–recapture analyses. Since its development in the early 1980s, the use of camera- trapping to study population size of large carnivores with distinctive natural marks has become an important tool for monitoring rare or cryptic species, or both, in a wide range of environments (Carbone et al. 2001; Karanth and Nichols 1998). This quantitative technique, which has relatively low labor costs, is noninvasive and causes minimal environmental disturbance (Henschel and Ray 2003; Silveira et al. 2003). However camera-trapping depends on capturing as many different individuals and as many photo-captures of each individual as possible (Karanth and Nichols 2002). Camera- trapping has been used to study a variety of felids, for example, tigers (Panthera tigris—Karanth et al. 2006), jaguars (Pan- thera onca—Maffei et al. 2004; Silver et al. 2004), pumas (Puma concolor—Kelly et al. 2008), ocelots (Leopardus pardalis—Dillon and Kelly 2007), bobcats (Lynx rufus—Kelly and Holub 2008), Geoffroy’s cat (Leopardus geoffroyi— Cuellar et al. 2006), and snow leopards (Uncia uncia—Jackson et al. 2006). The 1st estimation of Eurasian lynx (Lynx lynx) abundance by means of photographic capture–recapture was conducted in the northwestern Swiss Alps (NWSA) in 1998 (Laass 1999). It www.mammalogy.org 73