Abstract
To determine abundance, density and distribution of wild animals, it is crucial to estimate populations using reliable sampling techniques. In most earlier studies, elephant populations were estimated employing block counts or dung counts, which provide biased estimates due to limitations of the methods. We estimated an Asian elephant population using distance sampling, a quantitatively robust technique, in Biligiri Rangaswamy Temple Tiger Reserve, a critical elephant conservation area in the Nilgiri Biosphere Reserve in south India. We laid 33 transects with a total length of 93 km. We walked these transects five to 11 times amounting to a total of 795.5 km of walks. We collected data on location, number and age-sex classes through direct elephant sightings, using rangefinders, global positioning systems and compass. We used DISTANCE software for analysis. We estimated per km2 cluster density as 0.69 elephant herds, mean cluster size as 2.44, and elephant density as 1.7 animals. This amounts to a total of 713 elephants in 610 km2 of the sanctuary. A high percentage of males less than 30 years old and a low immature:adult female ratio indicated the severity of poaching in the recent past in the study region.
Highlights
Population estimation, either by direct or indirect surveys, is crucial to determine abundance, density and distribution of wild animals [1,2,3]
Use of the dung count method to estimate elephant densities is often limited by using known defecation rates [11] which are affected by factors such as season, rainfall, habitat types, size of boli etc. [12,13] or on the assumption of age-specific decay rates [14], thereby providing biased estimates
We carried out this study in the Biligiri Rangaswamy Temple Tiger Reserve, which lies between 110 40 ́-120 09 ́ N and 770 05 ́-770 15 ́ E, covering an area of 610 km2 (Fig. 1)
Summary
Population estimation, either by direct (observations) or indirect (nest or faecal) surveys, is crucial to determine abundance, density and distribution of wild animals [1,2,3]. [12,13] or on the assumption of age-specific decay rates [14], thereby providing biased estimates Population parameters such as density and age-sex ratios have been estimated using distance sampling based on direct or indirect signs [15], capture-recapture [16] and population surveys [4]. More recent methods such as photographic techniques and acoustic sensors have seldom been used to estimate abundance of elephants in dense forest areas [7, 17,18]. Distance sampling offers a reliable estimation of animal densities [19] comparable to results of the mark-recapture method, and has proved to be cost-effective and less disturbing to the environment [20]
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