India’s Tigers May Be Worse Off Than We Thought
India’s government spent January touting the success of its tiger conservation efforts, reporting the big cat’s population has jumped by a third since 2011.
Officials counted 2,226 tigers in 2014, compared with 1,706 three years earlier.
Now scientists at Oxford University are questioning the accuracy of the methods conservationists are using to determine tiger populations in the wild. That means critically endangered tigers may be in more trouble than we thought.
Arjun M. Gopalaswamy, lead author of the first-of-its-kind study, said the index-calibration method used to estimate animal population could have unacceptable shortcomings.
Here’s how a lot of animal count methods, including India’s, work: Researchers stake out a relatively small region with reliable animal detecting strategies, such as deploying motion-sensitive camera traps. They combine that data with animal tracking surveys and extrapolate those findings over a larger geographic area.
The problem is, the method isn’t reliable enough to obtain accurate estimates for an animal and can’t really be relied on to determine if a species is thriving or dying.
“Index-calibration models are so fragile that even a 10 percent uncertainty in detection rates severely compromises what we can reliably infer from them,” Gopalaswamy said in a statement. Looking at the Indian tiger survey, the scientists found the results extremely hard to replicate and most likely inaccurate.
Gopalaswamy said one of the main issues with index calibration is its assumption that tiger detection, whether by camera trap or by trackers identifying animal scat or tracks, is black or white—there is a paw print, or there isn’t—when often, there could have been a tiger paw print on the road that a passing truck wiped out.
“It relies on the assumption that detection rates of animal evidence are high and unvarying,” Gopalaswamy said. “In reality, this is nearly impossible to achieve.”
Still, researchers were quick to point out that they aren’t trying to rain on the Indian tiger’s parade, but they said any celebration of the endangered species' nascent recovery may be premature. The country is home to about 70 percent of the world’s 3,200 remaining tigers, and India’s management of its 40 tiger reserves around the country has become a model for other nations struggling to halt the species’ decline.
“We are not at all disputing that tiger numbers have increased in many locations in India in the last eight years, but the method employed to measure this increase is not sufficiently robust or accurate to measure changes at regional and country-wide levels,” said Ullas Karanth, a coauthor of the study and a member of India's National Tiger Conservation Authority.
The findings should help researchers better understand the weaknesses of such population estimates. The same method of counting animals has been used for mink and water vole species, study coauthor and Oxford professor David Macdonald said.
“It can work well if the correlations are tight and consistent, but often they aren't, and many of us, myself included, have been using the technique without appreciating its risks,” Macdonald said in a statement.