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article imageIndia's tiger census success story may be inaccurate, study says

By Megan Hamilton     Feb 26, 2015 in Environment
New Delhi - The accuracy of India's recent tiger census that suggested tiger numbers have increased is now being called into question by a new study.
The Indian government had celebrated the rise in tiger numbers from 1706 in 2011 to 2,226 in 2014.
This was considered to be a sign that state-led conservation efforts were working, The Guardian reports.
A team of scientists from Britain and India says the census likely suffers from a measuring error, but this is being contested by experts involved in the census. In fact, the issue is turning into an interesting scientific finger-pointing contest.
The controversy centers around what's known as the "index-calibration model," which measures animal numbers when they can't be observed in person, The Times of India reports. The model uses data from camera-traps and radio collars, among other methods. The technique is often used for the census of tigers and other rare animals worldwide.
The scientists say that they aren't disputing the rise in Indian tigers but the methodology supporting the census isn't strong enough to measure changes in population, The Guardian reports.
"This study exposes fundamental statistical weakness 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, the study's co-author and a member of India's National Tiger Conservation Authority. "We are not at all disputing that tigers 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."
The scientists involved in the census disagree.
"These inferences are unfair," Yadvendra D Jhala from the Wildlife Institute of India (WII) and a principal investigator involved in the census told The Times of India. "We use all published animal abundance methods; occupancy, capture-mark-recapture and distance sampling using the best technology of remote camera traps, see-through compasses, laser range finders and GPS."
"Mathematics does not get outdated," Jhala said after some said that the analytical tools used, especially regression and double sampling were "outdated."
He added:
"The analysis suggested by critics — the 'occupancy' method, which, incidentally, is used and reported in all our reports — also uses regression and double sampling."
Qamar Qureshi, a principal investigator in the census who is also from WII said he thinks the criticism stems from a lack of understanding. He noted that Karanth also suggested that tigers should be monitored yearly instead of the usual four-year countrywide assessment.
"This is being done," he said. "Around 80 percent of our tigers reside in 20 percent of the occupied area (protected forests). These source populations are being annually monitored by camera traps in all tiger reserves. It's known as phase IV monitoring and was envisaged by us way back in 2005."
Despite this, some doubt has been cast on the effectiveness of index-calibration models, The Deccan Chronicle reports.
"Our study shows that index-calibration models are so fragile that even a 10 percent uncertainty in detection rates severely compromises what we can reliably infer from them," said Arjun Gopalaswamy, a lead author of the report from the Wildlife Conservation Research Unit at Oxford University. "Our empirical test with data from Indian tiger survey efforts proved that such calibrations yield irreproducible and inaccurate results," Gopalaswamy said.
Index-calibration is a method that frequently relies on measuring animal numbers accurately in a small region using expensive and intensive methods and then relating the measure to an inexpensive indicator that is easier to obtain (like animal track counts, for instance) by means of calibration, The Deccan Chronicle reports.
The study authors tested the technique by using a mathematical model, and to do so, they employed tiger field work data and concluded that its predictive power wasn't reliable. This type of modeling also involves high and unvarying detection rates for animals, Gopalaswamy said. Tigers like to make use of man-made roads and the movements of vehicles, people, and cattle can make it more difficult to detect tiger tracks.
"Index-calibration relies on the assumption that detection rates of animal evidence are high and unvarying," he said. "In reality,this is nearly impossible to achieve. Instead, there are many flexible approaches, developed over the past decade by statistical ecologists, which can cut through noisy 'real world' data to make accurate predictions."
The study authors caution conservation practitioners to guard against errors that could derail the best conservation efforts. Instead, they suggest more constructive ways to use alternative methods of counting rare animals that avoid the pitfalls of the index-calibration approach.
Despite a long history of concern for wild tigers  both their range and total number have collapsed:...
Despite a long history of concern for wild tigers, both their range and total number have collapsed: fewer than 3,500 animals now live in the wild, occupying less than 7 percent of their historical range. Of these, approximately 1,000 are likely to be breeding females.
Tarique Sani
The Indian, or Bengal tiger calls India home, but there are also smaller populations in Bangladesh, Nepal, Bhutan, China, and Myanmar. While it is the most numerous of the world's tiger species it is still in dire trouble, The World Wildlife Fund (WWF) reports.
When India's tiger reserves were created in the 1970s, this helped stabilize the big cat's numbers, but once again, poaching is rearing it's ugly head to meet a growing demand in Asia. The mangroves of India's famed Sundarbans are the only mangroves where Bengal tigers can be found and rising sea levels are threatening these mangroves, the WWF reports.
Along with increased poaching, tigers have to contend with a severe loss of the prey they depend upon — like deer and antelopes, which are in decline due to poaching for meat and trade, and culling to prevent competition with livestock over food. Habitat degradation due to excessive tree cutting for fires also plays a part in reducing the numbers of these herbivores.
With the ongoing continuous loss of habitat and the prey that tigers depend upon, these magnificent big cats are coming into increasing conflict with humans as they attack domestic animals and people. In retaliation, villagers frequently kill tigers, the WWF reports.
Extinction is still a possibility for this beautiful big cat, so it is to be hoped that researchers can develop successful methods of keeping track of their numbers to keep them with us for generations to come.
This documentary is a fascinating look into the lives of tigers in the Sundarbans:
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