Do you know how they count tigers in the wild?
These are elusive creatures, after all, and hunt at night, so difficult to spot. They don’t actually amble over to greet the surveyors. They can’t be surveyed from the air unlike wildlife in the East African savanna as they can hide in the dense tropical jungles where they exist. Each tiger controls a large territory (between 0·25 and 19 tigers 100 km−2), thus the tiger density is low at the best of times.
The following methods are being used:
- Pug mark identification – highly subjective; accuracy questionable as the coefficient of variation (CV) is between 17-55%
- Camera trap mark recapture (CTMR) – more accurate with a CV of 13%. Below a certain density of tigers, this method does not work as no tigers may be photographed at all.
- Inference from prey densities – models predict tiger densities by counting prey densities when compared to CTMR. Although the coefficient of determination is high, since the gold standard used is CTMR, there is at least 14% variability in this method.
- Fecal DNA analysis – Uma Ramakrishnan from the National Centre for Biological Sciences, Bangalore, India, and her colleagues published a comparison of fecal DNA analysis and capture-recapture photographic identification in their publication “Biological Conservation
Volume 142, Issue 10, October 2009, Pages 2350-2360“. Ten microsatellite markers were used to identify tiger DNA from tiger scats (fecal remains). The standard error rate is about 13%. This is a convenient method as camera traps are quite expensive and cumbersome to set up (in the range of $2 million per country).
This will lead us to conclude that the exact number of tigers in the wild is uncertain due to the errors inherent in the methods used.
