Estimating densities of large herbivores in tropical forests: Rigorous evaluation of a dung‐based method

Abstract

When sighting‐based surveys to estimate population densities of large herbivores in tropical dense forests are not practical or affordable, surveys that rely on animal dung are sometimes used. This study tested one such dung‐based method by deriving population densities from observed dung densities of six large herbivores (chital, elephant, gaur, muntjac, sambar, and wild pig) in two habitats, dry deciduous forests (DDF) and moist deciduous forests (MDF), within Nagarahole National Park, southern India. Using the program DUNGSURV, dung pile counts, decay rates estimated from field experiments, and defecation rates derived from literature were analyzed together by a model that allows for random events affecting dung decay. Densities of chital were the highest, followed by sambar. Wild pig densities were similar in the two habitats, sambar densities were higher in DDF, and densities of the other species were higher in MDF than in DDF. We compared DUNGSURV estimates with densities estimated using distance sampling in the same season. DUNGSURV estimates were substantially higher for all species in both habitats. These differences highlight the challenges that researchers face in computing unbiased estimates of dung decay rates and in relying on defecation rates from literature. Besides the elephant, this study is the first to rigorously test the efficacy of using a dung‐based approach to estimate densities of large herbivore species in Asia, and based on this evaluation, we provide specific recommendations to address issues that require careful consideration before observed dung densities are used to derive animal densities. Our results underline the need for an experimental study of a known population in a fenced reserve to validate the true potential of using dung‐based approaches to estimate population densities.

Camera trapping reveals trends in forest duiker populations in African National Parks

“…; Ahrestani et al. ). Currently there are few published dung decay studies or defecation rates for most sites and species (Breuer et al.…”

“…This is especially troublesome when the duiker community is a mix of resilient and non-resilient species with different diets. To distinguish duiker species effectively, dung transect monitoring requires DNA analysis (Bowkett et al 2009;Ntie et al 2010), local dung decay rates estimated concurrently with the surveys, and defecation rates for all species in question (Viquerat et al 2012;Ahrestani et al 2018). Currently there are few published dung decay studies or defecation rates for most sites and species (Breuer et al 2009;van Vliet et al 2009a;Viquerat et al 2012).…”

High abundance and large proportion of medium and large duikers in an intact and unhunted afrotropical protected area: Insights into monitoring methods

“…Dung surveys with all their limits can still be informative, if on site dung decays are used and if species can be identified appropriately (Ahrestani et al., 2018). Using on site dung decay, results from this line transect dung survey elucidated the apparent differences of duiker estimates from other studies that have used dung decay rates from other sites.…”

Food and nutrition of Gaur (Bos gaurus C.H. Smith, 1827) at the edge of Khao Yai National Park, Thailand

“…Ungulate species have been found to have different food and feeding habits 43 . Gaur, have been described as grazers 42,44,45 , browsers 46 and generalists 47 depending on habitat types.…”