Deriving a population estimate for Eld’s deer (Rucervus eldii siamensis) in Siem Pang Wildlife Sanctuary, Cambodia

Context Eld’s deer (Rucervus eldii) was once widely distributed across Southeast Asia but is now endangered. The strong hold of the subspecies R. e. siamensis is largely restricted to north and east Cambodia, with only small, spatially isolated populations known to occur. Aims To assess if camera traps and spatial capture–recapture methodology can estimate population size of Eld’s deer in Siem Pang Wildlife Sanctuary (SMWS). Methods Infra-red and white flash camera traps were set at 83 grid-point locations (83 km2) over a 5-month sampling period and used a Spatially Explicit Capture Recapture (SECR) model to estimate population size, relying on natural markings to identify males and using sex ratios to extrapolate a population estimate. Key results We estimated the number of Eld’s deer in SMWS to be 272 (95% CI: 169–435). We affirmed that white flash camera traps are advantageous in identifying individuals without significantly affecting detection probability. Conclusions Monitoring the small and difficult to detect subpopulations of R. e. siamensis is challenging. Camera traps can be used although there are challenges to resolve when using the SECR model that can be improved by using white flash cameras to improve the identification of individuals, and assisted with sex and age determination. Implications The SPWS population may potentially be the largest of the R. e. siamensis subspecies in Southeast Asia and it is therefore of critical conservation importance that long term camera trap monitoring is established.