Camera trap distance sampling for density estimation of tiger prey in a Sumatran ecosystem restoration concession

Estimating prey species densities is critical for implementing effective tiger Panthera tigris recovery strategies. Several statistical models exist for density estimation of unmarked species from camera trap data, all of which rely on the random placement of cameras. This has limited the use of such models, as random camera trap placement is often viewed by field conservationists as impractical and inefficient, particularly in landscapes where ungulates are rare. We used camera trap distance sampling (CTDS) to estimate the density of prey species from randomly placed cameras within an ecosystem restoration concession in central Sumatra. We estimated densities of two species: southern red muntjac Muntiacus muntjak (2.14 ± SE 0.8 individuals per‐km2) and southern pig‐tailed macaque Macaca nemestrina (6.43 ± SE 1.2 individuals per‐km2). These represent the first quantitative density estimates for these species from tiger landscapes within the Sundaic forests of South‐east Asia. Uncertainty around the density estimates was likely due to the low sample size of camera trap locations, which led to high variability in the number of encounters between camera traps. Whilst detections of other tiger prey species (i.e. sambar Rusa unicolor, wild pig Sus scrofa, bearded pig S. barbatus) were insufficient to estimate density, trap success rates of these species were higher than camera traps set in a conventional tiger‐focused grid. Complementary camera trap survey designs that implement both targeted and randomized placement designs are likely to provide a better picture of carnivore populations and critical resources, whilst minimizing bias, in Asian tropical forests. Tiger prey density within the site is low, presumably due to a combination of gun‐hunting of ungulates by local communities, and disease, particularly African swine fever affecting pig species. Recovering tigers across the extensive rainforests of Sumatra will require targeted ungulate hunting reduction and active prey recovery, particularly focusing on sambar and wild pigs.