Methods for estimating population densities of unmarked species using camera traps are still under development. One such method 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 method to estimate the density of Balkan chamois (Rupicapra r. balcanica) in a Mediterranean habitat, Mt. Biokovo. To meet the assumptions of REM, we systematically placed 25 camera traps throughout the known range of the population (approximately 65 km²) at the intersections of 2-km grid cells. 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-h period. All parameters for REM (i.e. average movement speed, angle and radius) were estimated using exclusively camera trap data. We obtained 279 independent events of chamois from 2503 camera trap days. The density estimate obtained by REM resulted to be 20.65 ± 5.27 ind. km⁻², slightly higher than the reference value obtained by visual counts: 17.33 ± 0.98 ind. km⁻². Other parameters required to calculate density were speed (1.62 km·day⁻¹ ± 0.21), detection radius (5.56 m ± 0.21) and detection angle (1.16 + 0.05 radians). Therefore, REM has shown comparable results to visual counts and may have potential for estimating density of mountain ungulates, especially in rugged and inaccessible mountainous areas with low detectability where other approaches are inadequate or impossible.

使用相机陷阱估计未标记物种种群密度的方法仍在开发中。其中一种方法被称为“随机遭遇模型（REM）”，据我们所知，它从未被用于估计山地有蹄类动物的密度。在这项研究中，我们测试了 REM 方法来估计地中海栖息地比奥科沃山中巴尔干羚羊 ( Rupicapra r. balcanica )的密度。为了满足 REM 的假设，我们系统地在种群的已知范围内（大约 65 公里²) 在 2 公里网格单元的交叉点。在收集数据之前，通过 2020 年 8 月对样本地块的视觉计数估计人口密度。摄像机在 2020 年 7 月至 2020 年 9 月期间运行，并在整个 24 小时期间处于活动状态。REM 的所有参数（即平均移动速度、角度和半径）都是使用专门的相机陷阱数据估算的。我们从 2503 个相机陷阱日中获得了 279 个独立的麂皮事件。REM 获得的密度估计结果为 20.65 ± 5.27 ind。km ^-2，略高于目测获得的参考值：17.33 ± 0.98 ind。公里^-2。计算密度所需的其他参数是速度（1.62 公里·天^-1± 0.21)、探测半径 (5.56 m ± 0.21) 和探测角度 (1.16 + 0.05 弧度)。因此，REM 已显示出与目视计数相当的结果，并且可能具有估计山地有蹄类动物密度的潜力，尤其是在其他方法不充分或不可能检测到的崎岖和难以进入的山区，检测性低。