engleski

Random encounter model to estimate density of Balkan chamois

Reliable estimation of wildlife density and population size is the crucial basis for the successful implementation of wildlife management and conservation. As a non-invasive and easily affordable tool, camera traps are commonly used to monitor wildlife. However, estimating population density using camera traps is challenging, but several methods conducted on individually recognizable species have shown good performance, such as spatial capture-recapture and mark-resight. Conversely, methods for estimating population densities of unmarked species using camera traps are still developing. One of these methods is called "Random Encounter Model (REM)" and, to our knowledge, has never been used to estimate densities of mountain-dwelling ungulates. In this study, we tested the REM to estimate the density of Balkan chamois (Rupicapra r. balcanica) in a Mediterranean habitat, Mountain Biokovo. We proportionally placed 25 camera traps throughout the known range of the population distribution (ca. 55 km2) at the intersections of 2-km grid cells to meet the assumptions of REM. Prior to data collection, population density was estimated by visual counts on sample plots in August 2020. Cameras were operational between July 2020 and September 2020 and active throughout the 24-hour period. We obtained 279 independent events of chamois from 2503 camera trap days. Other variables required to calculate density were speed (1.62 ± 0.21 km/day), detection distance (5.56 ± 0.20 m) and detection angle (1.16 + 0.05 radians). The density estimate obtained by REM resulted to be 20.65 ± 5.27 ind/km2, slightly higher but not significantly different (Wald test, p = 0.61) than the reference value: 17.33 ± 3.64 ind/km2. The CV value of 0.25 obtained by REM was satisfactory, considering low number of trap-sights. Therefore, REM has shown comparable results to visual counts and may have potential for estimating density of mountain ungulates, especially in mountainous areas with dense vegetation cover where other approaches are inadequate.

camera trapping, mountain ungulates, REM, rupicapra balcanica, ungulate density

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