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.
Highlights
Large herbivores are integral to terrestrial habitats across the Earth and as primary consumers are key to food webs and the functioning of ecosystems they inhabit (Gordon, Hester, & Festa-Bianchet, 2004; Malhi et al, 2016)
We counted dung piles of six large herbivore species in plots located within two major habitats: dry deciduous (DDF) and moist deciduous (MDF) forests found within Nagarahole National Park, southern India (Figure 1)
We reported estimates using the first three3 stages of decay. 2/3/4 indicates the number of decay stages for which the densities were determined; that is, no dung piles from the earliest sample were found in these decay stages at the time of the survey
Summary
Large herbivores are integral to terrestrial habitats across the Earth and as primary consumers are key to food webs and the functioning of ecosystems they inhabit (Gordon, Hester, & Festa-Bianchet, 2004; Malhi et al, 2016). The need to accurately estimate abundances of large herbivores has, never been greater. Because of the difficulty of seeing animals in dense vegetation, deriving reliable estimates of large herbivore abundance in tropical forested landscapes has been problematic. Researchers and managers have, attempted to estimate populations of large herbivores in tropical forests from their signs, instead of relying on direct observation of individuals (Kohn & Wayne, 1997; Putman, 1984). The most visible sign of a large herbivore in a forest is its dung, which it normally drops in a pile. These dung piles are relatively easy to find, identify, and count in forested habitats
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