Sampling design and analytical advances allow for simultaneous density estimation of seven sympatric carnivore species from camera trap data

Abstract

Population density is a fundamental parameter needed to assess wildlife populations but is difficult to obtain given species are often wide-ranging and elusive. Photographic capture-recapture techniques do not require direct observations and thus, have become a common approach for estimating wildlife densities. To date, however, these studies have typically focused on single species. Our research explores study design- and analytical-based approaches for expanding photographic capture-recapture studies to assess multiple species simultaneously. We developed a hybrid-sampling scheme that varied inter-camera distances and used simulations to test the efficacy of this design versus a systematically spaced grid in estimating densities of species with varied space use. Through simulations we found the hybrid design facilitated density estimates for a wider range of species with little or no cost in accuracy for most species. We implemented a hybrid camera design across a 1154-km2 area in northern Botswana to estimate densities of lions, spotted hyenas, leopards, wild dogs, servals, civets, and aardwolves. We estimated densities of these small- to wide-ranging carnivores, where all or some portion of the population was individually identifiable, using spatially explicit capture-recapture and mark-resight models. Mean estimates ranged from 1.2 (95% CI = 0.72–1.99) lions to 10.1 (95% CI = 8.69–11.63) spotted hyenas/100 km2 and provided empirical information needed for the conservation of these species in Botswana. Our research demonstrates how photographic capture-recapture studies can be expanded to estimate the densities of multiple species versus just a single species within a community, thus increasing the conservation value of this globally implemented approach.