Random encounter model to estimate density of mountain-dwelling ungulate

• Published in: European journal of wildlife research Vol. 67; no. 5
• Main Authors: Kavčić, Krešimir, Palencia, Pablo, Apollonio, Marco, Vicente, Joaquín, Šprem, Nikica
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-10-2021; Springer Nature B.V
• Subjects: Biomedical and Life Sciences; Cameras; Data collection; Ecology; Estimation; Fish & Wildlife Biology & Management; Life Sciences; Mountain regions; Mountainous areas; Mountains; Original Article; Parameters; Population density; Population statistics; Traps; Ungulates; Zoology; Density estimation; Mountain ungulate; Camera trapping; REM; Northern chamois
• ISSN: 1612-4642; 1439-0574
• DOI: 10.1007/s10344-021-01530-1

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 km
2
) 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.