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Scientists stress need for replacing Dung-based methods to estimate herbivore densities by more robust approaches

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by VIJAYKUMAR PATIL

Belagavi, Sept.30: The latest study has raised concerns over the reliability of elephant population monitoring using the dung-based methods used in India and parts of Africa and suggested the need to replace the dung-based methods to estimate herbivore densities by more robust approaches.

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Scientists conduct a study to rigorously test the efficacy of a dung-based approach in estimating large herbivore densities (chital, elephant, gaur, muntjac, sambar, and wild pig) in Nagarahole National Park.

Estimates obtained from the dung-based method were consistently higher than those from sighting-based methods.

The study urges evaluating the effectiveness of dung-based approaches in surveying population densities.

The study tested large herbivore density calculations including those for gaur (Copyright: Siddhesh S. Nimkar)
The study tested large herbivore density calculations including those for gaur (Copyright: Siddhesh S. Nimkar)

The study highlights the importance of calculating unbiased estimates of dung decay: “The study reinforced earlier research that methods that involve counts of animal spoor counts have inherently low information content and it is hard to extract reliable information from such data and calibrate them against rigorous methods which are reliable but very intensive and difficult to implement at extensive scales. This study raises concerns about the reliability of elephant population monitoring using dung-based methods, which are in use in India and many parts of Africa,” elaborates Dr.K. Ullas Karanth, Director, Centre for Wildlife Studies (CWS) and co-author of the study.

Densities of chital were found to be highest in both forest types chosen (Copyright: Avinash Satamraju)
Densities of chital were found to be highest in both forest types chosen (Copyright: Avinash Satamraju)

The paper titled “Estimating densities of large herbivores in tropical forests: Rigorous evaluation of a dung-based method” was published was authored by Dr.Farshid S. Ahrestani and co-authored by Srinivas Vaidyanathan from Foundation for Ecological Research, Advocacy and Learning (India); Dr.N. Samba Kumar, Dr.Devcharan Jathanna, Dr.Karanth and Mr. Lex Hiby from Conservation Research Ltd (UK). This scientific paper was published in the international journal Ecology and Evolution recently and it can be accessed online at https://doi.org/10.1002/ece3.4227.

The study tested a dung-based method of estimating herbivore population density in Nagarahole National Park in the south Indian state of Karnataka. It was found that the estimates were significantly higher than the numbers measured by sighting-based distance sampling. However, due to differences in results obtained, the authors emphasised caution and suggested that more robust approaches be incorporated by scientists and managers as density estimates of threatened herbivores need to be reliable for successful conservation action.

Elephant densities were higher in moist deciduous forests (Copyright: Ramki Sreenivasan)
Elephant densities were higher in moist deciduous forests (Copyright: Ramki Sreenivasan)

The scientists from CWS in collaboration with Foundation for Ecological Research, Advocacy and Learning [FERAL] (India); and Conservation Research Ltd (UK), in their test of a dung-based method of estimating herbivore population density in Nagarahole National Park, found that the estimates were significantly higher than the numbers measured by sighting based distance sampling. Due to the differences in results obtained, the scientists emphasised on the need to conduct an experimental study of a known population in a fenced reserve to determine the validity of using dung-based approaches in population density estimations.

The study estimated and compared large herbivore densities for chital, elephant, gaur, muntjac, sambar, and wild pig. Dung pile counts, decay rates estimated from field experiments and defecation rates derived from literature, were utilised to construct models using program DUNGSURV in moist and dry deciduous forests.

Wild pig densities were found to be similar in both types. Sambar were found in a higher concentration in the dry deciduous terrain. The other four species (gaur, chital, muntjac, and elephant) were found to be higher in the moist deciduous forests. The DUNGSURV density estimates were found to be significantly higher than the line transect results in both types of forests.

Dr. Ahrestani, the lead author and (Senior Doctoral Fellow, FERAL) observed and said: “Large ungulates are a highly threatened group of animals, and this study was an attempt to calibrate a widely-used dung-count base ungulate monitoring methodology against the rigorous well-established method of line transect sampling. We used large, rigorously gathered data sets on both approaches collected by Centre for Wildlife Studies and performed advanced analyses using statistical models of dung decay rates to derive our conclusions.”

Further, Dr.Karanth states that this study highlights the importance of calculating unbiased estimates of dung decay: “The study reinforced earlier research that methods that involve counts of animal spoor counts have inherently low information content and it is hard to extract reliable information from such data and calibrate them against rigorous methods which are reliable but very intensive and difficult to implement at extensive scales. This study raises concerns about the reliability of elephant population monitoring using dung-based methods, which are in use in India and many parts of Africa.”

He said that the study concluded observing that despite the infeasibility of using visual methods for population estimates, the simplistic application of dung-based approaches could lead to inaccurate results.

The team of scientists strongly recommends that the use of dung-based techniques must be informed by careful consideration of factors that induce bias. The authors urged caution and suggested that more robust approaches need to be incorporated by scientists and managers as density estimates of threatened herbivores need to be reliable for successful conservation action.

About CWS

The Centre for Wildlife Studies, based in Bengaluru, is an internationally recognized centre-of-excellence in the areas of wildlife research, in situ conservation, policy and education. In collaboration with Central and State Governments as well as partnerships with several national and international institutions CWS practices science-based conservation to promote the protection of wildlife and wildlands. (Visit: http://www.cwsindia.org/ Follow: @cwsindia [Instagram] | @cwsindia [Twitter] | https://www.facebook.com/cwsindia [Facebook]). Contact: [email protected]

Trinity Belagavi
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