The conservation of tiger populations requires the preservation of their prey. Assessing prey populations is therefore important, but challenges arise due to the elusive nature of many prey species. We used two indirect methods to estimate the density of sika deer (Cervus nippon), an elusive tiger prey species, in the Sikhote-Alin Biosphere Reserve in the Russian Far East. The fecal accumulation rate (FAR) is widely used and provides estimates of ungulate density based on the accumulation of fecal pellet groups in previously cleared plots. More recently, the random encounter model (REM) was developed to estimate population density from the rates of contact between study animals and camera traps. Its use is controversial because of questions on how to define an encounter, estimate daily travel distance, and adjust for herds. The goal of this project was to compare density estimates from the two techniques and assess whether and when REM could replace FAR in such surveys. Detectability of the study animals was similar for both methods, but the FAR technique yielded a much higher density estimate, 13.97 ± 2.74 standard error (SE) sika deer km-2 than did the REM method 4.91± 1.76 (SE) sika deer km-2, which was closer to expectation based on previous studies. Both methods required estimates from outside studies: of defecation rates for FAR and of average travel distances for REM. REM also required an assumption on group sizes which were likely underestimated in the camera images. Our analysis suggests theoretical considerations and practical adjustments that must be made to both methods when estimating population density. We also propose integrating the two techniques by using the camera traps over cleared plots to estimate defecation rates directly from the study population. Overcoming challenges like these is vital to designing effective conservation plans for tigers and their prey
