Bangalore: The Royal Bengal tigers are disappearing from Indian forests and national parks. So is the people’s faith in the official census, whose every new estimate raises a public outcry.
Estimates of the tiger population vary, even though the non-scientific pug marks method of tracking tigers has lately given way to the more accurate camera-trap method.
In the pug mark method, tiger footprints are taken as the most reliable method of counting, though the method is not standardized.
The camera-trap takes photographs of the animals in their habitat and identifies them by their stripes, which are unique to each animal.
On the trail: Samrat Mondol, a researcher from NCBS, collecting tiger poop in the forest for genetic analysis of the population. NCBS
Now, a team of geneticists at the National Centre for Biological Sciences (NCBS) in Bangalore in collaboration with conservationist K. Ullas Karanth, who pioneered the camera-trap method in the mid 1990s, has developed a genetic tool to estimate the population of tigers by using DNA (Deoxyribonucleic acid) from their fecal matter. The scientists report their technique in the forthcoming issue of the journal Biological Conservation.
Even though the camera-trap method is established now, sometimes it’s not amenable for use, especially when the population density is too low to be captured by cameras.
It is also not used in regions where there is a risk of cameras getting stolen or vandalized or washed away by high tides, as it happens in the Sundarbans.
“Genetics provides a good supplementary tool, especially because the sophisticated science is needed in the lab, not in the field, where sample collection can be done even by low-skill people,” said Karanth, senior conservation-scientist at Wildlife Conservation Society (WCS) and director of the Centre for Wildlife Studies in Bangalore.
Genetic data for population estimation is being used in some parts of the world on other low-density, elusive carnivores, but it’s for the first time being used on tigers, said researcher Uma Ramakrishnan from NCBS.
In India, the Centre for Cellular and Molecular Biology in Hyderabad has used genetic data for identification of individual tigers, but not for population estimates.
Studying the tigers in the Bandipur Tiger Reserve, where Karanath’s team has been photographing the big cats annually for the last 10 years, researchers could compare the estimates from the two methods—camera-trapping and genetic analysis. The result, they say, is very encouraging as the two population estimates matched very well.
“We have developed the proof-of-principle, which is essential for evolving a common national technique, since there isn’t much communication between different groups studying tigers in this country,” Ramakrishnan said.
The genetic method, though still in the research stage globally, has “lot of potential”, said S.P. Goyal, senior scientist at the Dehradun-based Wildlife Institute of India (WII), which is one of the agencies involved in the tiger census in India.
But before it gets popularly adopted, it needs to be verified at multiple locations as well as in different seasons in one tiger reserve for at least two years, he added.
WII is using the three methods—pug mark, camera- trapping and an experimental genetic tool—in the Ranthambore National Park.
But all studies don’t require long-term sampling.
If one needs to answer how many tigers are there at a given point in time, said Karanth, then the sampling, with cameras or scats, should be completed in as short a period as possible.
This is because the population is turning over continually through births, deaths, emigration and immigration. This is called “demographically closed model analysis”.
For the present study, there were six sampling occasions over a period of 42 days, involving 18 routes in the Bandipur National Park.
However, if Goyal’s concern is about the quality of DNA, Ramakrishnan says her team has collected scats from across the Western Ghats over the last few years in different seasons and has shown similar success in DNA extraction and individual identification.
In fact, the department of science and technology in New Delhi and New York-based WCS has jointly funded a project to apply this technique to a larger region in the Mysore-Malnad region, in south-western Karnataka, for studying the tiger population.
“The best thing about combining the two techniques is that it is soundly grounded in field ecology,” said Ramakrishnan.