Sampling tiger ungulate prey by the distance method: lessons learned in Bardia National Park, Nepal. Wegge, P. & Storaas, T. Animal Conservation, 12:78–84, 2009.
abstract   bibtex   

Because tiger Panthera tigris numbers are regulated by their prey base, prey abundance needs to monitored and estimated reliably. Recently, distance sampling has been adopted as the most appropriate method and is now becoming the standard monitoring protocol in all tiger range countries in south Asia. However, the accuracy of the density estimates generated by this method has not been assessed. From total counts within habitat blocks, we obtained accurate density estimates of ungulates within three main habitats in Bardia National Park, Nepal. We then applied the distance sampling method in the same habitats and compared the results. Distance sampling on foot in dense habitats (riverine forest and tallgrass floodplain) violated method assumptions, and sampling from vehicle along roads gave biased estimates. Sampling from elephant back worked well in all habitat types, but owing to their behaviour, the density of barking deer Muntiacus muntjak was underestimated. The accuracy of the estimates varied with sampling effort; for the very abundant chital deer Axis axis, estimates varied markedly at <200 animal observations, but converged at larger sample sizes to a similar point estimate as intensive block counts when approaching 300 observations. For the less abundant species, with <20 observations along >100 km of transect lines, the confidence intervals were quite high, and, hence, of limited value for detecting short-term populations trends. It is therefore difficult to obtain accurate density estimates of rare species by the distance method. In areas consisting of dense habitats, we recommend that the food base of tiger be estimated by distance sampling from elephant back, not on foot, directed at the main and most abundant prey species. For rare species, encounter rates obtained simultaneously may then serve as indices of relative abundances.
@ARTICLE{WeggeFebruary2009,
  author = {Wegge, P. and Storaas, T.},
  title = {Sampling tiger ungulate prey by the distance method: lessons learned
	in {Bardia National Park, Nepal}},
  journal = {Animal Conservation},
  year = {2009},
  volume = {12},
  pages = {78--84},
  abstract = {<P></P>Because tiger <I>Panthera tigris</I> numbers are regulated
	by their prey base, prey abundance needs to monitored and estimated
	reliably. Recently, distance sampling has been adopted as the most
	appropriate method and is now becoming the standard monitoring protocol
	in all tiger range countries in south Asia. However, the accuracy
	of the density estimates generated by this method has not been assessed.
	From total counts within habitat blocks, we obtained accurate density
	estimates of ungulates within three main habitats in Bardia National
	Park, Nepal. We then applied the distance sampling method in the
	same habitats and compared the results. Distance sampling on foot
	in dense habitats (riverine forest and tallgrass floodplain) violated
	method assumptions, and sampling from vehicle along roads gave biased
	estimates. Sampling from elephant back worked well in all habitat
	types, but owing to their behaviour, the density of barking deer
	<I>Muntiacus muntjak</I> was underestimated. The accuracy of the
	estimates varied with sampling effort; for the very abundant chital
	deer <I>Axis axis</I>, estimates varied markedly at &#60;200 animal
	observations, but converged at larger sample sizes to a similar point
	estimate as intensive block counts when approaching 300 observations.
	For the less abundant species, with &#60;20 observations along &#62;100&#8201;km
	of transect lines, the confidence intervals were quite high, and,
	hence, of limited value for detecting short-term populations trends.
	It is therefore difficult to obtain accurate density estimates of
	rare species by the distance method. In areas consisting of dense
	habitats, we recommend that the food base of tiger be estimated by
	distance sampling from elephant back, not on foot, directed at the
	main and most abundant prey species. For rare species, encounter
	rates obtained simultaneously may then serve as indices of relative
	abundances.},
  owner = {Tiago},
  subdatabase = {distance},
  timestamp = {2009.04.27}
}

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