BHUBANESWAR: Two thousand, nine hundred and sixty-seven (2,967) is the new magical number for India — the total tiger count after the fourth cycle of National Tiger Assessment which reveals the country’s remarkable turn-around in big cat conservation. But, behind this glad tidings is an equally astounding feat, now being billed as world’s largest biodiversity study.
Over 44,000 field staff of Forest Departments in 20 tiger-bearing States put in 5.94 lakh man-days to generate data. When the first phase of the tiger assessment kicked off in Jan-Feb 2018, the front-line forest staff were on the field for 10 days capturing evidence. And they surveyed a staggering 3.82 lakh sq km of forests, which included 5.23 lakh km on foot. At least 3.18 lakh habitat plots were samples for vegetation and prey dung.
So, what goes into the massive exercise that has caught the attention of the world? Months of planning and implementation, humongous man-power, back-breaking coverage of forest tracts and when the data is generated, new technology is used to filter the gigantic volumes of data. Since 2006 when it all began, the pan-India exercise has only grown in size, scale, manpower, technology and research that it involves.
Behind it are NTCA, its Tiger Cell, Wildlife Institute of India, country’s top wildlife research agency which coordinates all the efforts with State Forest Departments, conservation NGOs and lots of analytical minds to ensure that the final outcome stands test of every scrutiny.
The first phase is the key sign survey during which evidence of tigers, co-predators, prey density, vegetation, habitat quality and human impact are collected. Earlier, the forest staff used to find tiger signs in terms of, say, scats or pug-marks, and note down GPS coordinates on a piece of paper which were then punched into a computer. This process of generating sign evidence with GPS coordinates and transfer to computers for analysis carried chances of mistakes.“But M-STrIPES ((Monitoring System for Tigers-Intensive Protection and Ecological Status — a GPS-based android app) simplified it by tracking kilometers covered and pictures of signs with geo-tagging. You can’t fudge it. All this is transmitted digitally to us for analysis. New improvements have been added this time which is used for patrolling in 50 tiger reserves in India,” explained Wildlife Institute of India scientist, YV Jhala, one of the most distinguished field biologists of the country.
During the survey, each team of two field staff perambulates 5 km a day for three days. Then a 2-km line transect method is followed during which signs, prey density, habitat characteristics, interference of humans are collected.“This forms the basis for the next phase when camera traps are installed, as sites, where tiger evidences are found, is recorded and range distribution is calculated,” he said.The spatial coverage in the first phase is followed by remote sensing data of the landscapes, the habitat details and anthropogenic impacts in Phase-II, which takes into account forest size, topography, distance from core areas, human habitations, road network and other details.
Camera traps, analysing data
Called Capture-Mark-Recapture, this stage includes individual capture of photos to determine density and abundance of large cats.“The number of cameras used has gone up though the area which is sampled remains the same. Camera trap gives you reliable info because those are close to truth,” Jhala said.
How many photographs did the camera traps generate? 3.5 crore which included tigers, leopards, other carnivores, co-predators and prey species.Using specific models that identify the unique stripe patterns (for tigers) and spots (for leopards), individual animals were narrowed down. This process put the individual tiger photographs at 2,461. This number remains one of the benchmarks for the final tiger population estimation which is determined using the Spatially Explicit Capture Recapture (SECR) model.“The model uses co-variates such as sign encounter rate, prey encounter rate, human impacts and remotely-sensed data to arrive at the tiger estimation for individual tiger landscapes and the total number stood at 2,591,” the NTCA chief said.The number of individually camera-trapped tigers (2,461) is 83% of the tiger population of 2,967 whereas what SECR formula generated is 87% of it. The rest 13% was calculated using an extrapolation method from areas which are not camera trapped.
For the first time, tigers above 1 year have been brought under enumeration. Earlier, only those above 1.5 year were estimated. The survey also given a huge volume of photos of other animals and signs that can be analysed later.