Tiger Populations May Not Be on the Rise After All

Despite what recent research has said, tiger populations may not be on the rise after all, thanks to a flawed and inaccurate census method commonly used by scientists.

Known as the "index-calibration" technique, it involves using camera trapping and other methods to measure animal numbers in a relatively small region, and then relating this measure to an indicator, such as animal track counts, by means of calibration. The calibrated-index is then used to extrapolate actual animal numbers over larger regions.

And now a team of scientists from the University of Oxford, Indian Statistical Institute, and Wildlife Conservation Society are revealing for the first time the shortcomings of this approach, which can produce inaccurate results.

It is believed that among the recent studies based on index-calibration is that which reported that the population of India's iconic tigers was up 30 percent.

These new findings, published in the journal Methods in Ecology and Evolution, highlight the need for alternative methods of counting tigers and other rare wildlife, as well as have important implications in conservation efforts.

"This study exposes fundamental statistical weaknesses in the sampling, calibration and extrapolations that are at the core of methodology used by the Government to estimate India's numbers, thus undermining their reliability," Dr. Ullas Karanth, a co-author from the Wildlife Conservation Society, said in a news release. "We are not at all disputing that tigers numbers have increased in many locations in India in last 8 years, but the method employed to measure this increase is not sufficiently robust or accurate to measure changes at regional and country wide levels."

To investigate index-calibration, the researchers created a mathematical model describing the approach and then tested its efficiency when different values were put in. The majority of the time, the model was shown to lose its efficiency and power to predict. Even when applied to real world examples, the method was proved to be inaccurate.

"This is a breakthrough which will dramatically change how we count wildlife numbers in the future," co-author David Macdonald concluded.

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