By K. Ullas Karanth
An obsolete model incapable of spearating the signal from the noise – generating data not open to scrutiny – cannot be trusted to give a reliable count
Time is running out for the 3,000 tigers now guessed to be surviving in the wild. Tiger habitat shrank by 93% in the past two centuries. Today, the small populations with any hope of recovery now cling on to a mere 6% of what remains. Like a patient under intensive care, each population needs accurate, real-time monitoring.
With just 25% of world’s tiger habitat, India shelters 70% of its tigers. In a country with 1.2 billion people and the world’s 10th largest economy this is a remarkable fact. So when the Indian government recently trumpeted a 30% rise in its wild population of one of the world’s most popular animals, everyone cheered. But is that number real – or even useful?
In1972, when prime minister Indira Gandhi committed her government to bringing tigers back from the brink, her officials devised a counting method that had no basis in biology or statistics. The so-called “pugmark census” unrealistically hoped to identify every wild tiger from its paw-prints.
That tiger census approach, which was demonstrated to be flawed by conservation scientists, suggested that tiger numbers grew to more than 4,000 by 2004. But in the following year, after two high-profile reserves claiming large tiger populations were exposed to have none at all, the pugmark census was discredited and discarded. Government officials suddenly denounced their own approach as “trash,” then unaccountably turned to an obsolete statistical method revived from the 1930s.
Since then, three ‘national tiger estimation’ surveys have been completed (in 2006, 2010, and 2014). Each involved 90,000 man-days of labour spread over 400,000 sq km of forests and at a cost of 120m rupees (£1.2m) to Indian taxpayers. Armies of poorly trained foot soldiers collected a bewildering array of data, including tiger photos from automated camera traps, as well as counts of tiger tracks and droppings.
The massive piles of data were then crunched through a creaky statistical model incapable of separating the ‘signal’ from the ‘noise.’ These analyses, conducted under great secrecy, have generated the government’s tiger numbers. Not available for independent replication, India’s tiger data appears to be more elusive than the cat itself.
Nor do these survey results appear ecologically reasonable. Between 2006-2010, the government claims that although tiger habitat shrank by a whopping 22%, tiger numbers rose 16%, implying an unrealistic 49% leap in tiger densities within India’s beleaguered reserves. The recent claim of another 30% jump in the next four years stretches credulity even further. Estimated leaps of over 100% in just four years, reported for some states, are also not plausible.
Concerned by these apparent anomalies, some of us from the Wildlife Conservation Society, Oxford University, and the Indian Statistical Institute tried to evaluate the government’s models, in which counts of tiger tracks were compared to tigers photographed in small areas to provide an estimate for region-wide populations. While the government claimed the two measurements agreed with 99% accuracy, we barely attained 5% when we replicated the effort.
And yet, instead of providing a reasoned scientific response to our critique, Indian officials ignore necessary improvements.
Almost 90% of India’s tigers are now concentrated in a few ‘source populations’ that cover just 10% of tiger habitat. Because of serious threats, these populations must be counted accurately yearly. Camera-trap photography can provide reliable counts, but only if rigorous statistical protocols are employed. Under rigorous protocols camera traps can reveal not only whether each tiger population is increasing or declining but also how many tigers it is losing or gaining.
Our work in the Malenad landscape in Western Ghats of southern India, for example, shows that tiger populations vary from a high of 8-15 tigers/100 sq km in well-protected reserves to a low of 1-5 tigers/100 sq km in less secure ones. Interestingly, even the thriving populations lose 20% of their tigers annually – from fights, human conflict, and poaching. They remain viable because of high reproduction rates.
If rigorous monitoring of source populations can work effectively in Malenad, which holds one-fifth of India’s tigers, it can work equally well for other tiger populations across the country, potentially helping conservationists to track the fate of 90% of India’s tigers in real time.
Now is the moment to radically revamp not just the obsolete national tiger estimation method, but also the present bureaucratic monopoly over auditing of wildlife conservation in India. In their place, a public-private partnership that freely and transparently taps into the wellspring of talent and resources of India’s scientists, non-governmental organisations, and the private sector should be adopted.
But make no mistake. If we continue to ignore the necessary, independent, real-time tiger monitoring any longer, instead of nursing the world’s favourite animal back to health from intensive care, we will be pulling the plug on it.