Decoding Tiger Census 2018: WII scientist explains method, talks about the smaller tiger populations gone extinct – India Today

By Roshni Chakrabarty: On International Tiger Day 2019, July 29, PM Narendra Modi released the tiger estimation figures in India and said that the country had achieved its target of doubling its number of tigers an incredible four years earlier than the given deadline. Now, India has 2,967 tigers – a reported growth of 33% in the fourth cycle of the Tiger Census which has been conducted every four years since 2006.

In 2006, the census showed that the number of tigers in India was only 1,411. In the next cycle of 2010, the numbers grew to 1,706, and in 2014, the tiger numbers grew to 2,226.

As per the Tiger Census of 2018, the state of Madhya Pradesh has the highest number of tigers at 526. It is followed by Karnataka with 524 tigers and Uttarakhand at 442 tigers. However, the states of Chhattisgarh and Mizoram saw a decline in tiger numbers while Odisha maintained its population.

PM Modi said that today, India was one of the safest habits for tigers in the world. But is the picture really this rosy?

News of the 2018 Tiger Census came amidst a viral video of an adult tigress being beaten to death by a mob in an Uttar Pradesh village on an agricultural field within range of the Pilibhit tiger reserve.

With India’s growing population and rampant deforestation, it is most definitely not a good time to be a tiger even if the numbers have steadily continued to increase in the country.

We got talking to Dr Yadvendradev Jhala, a Wildlife Institute of India scientist and one of the coordinators of the tiger survey alongside Prof Qamar Qureshi, regarding how the Tiger Census 2018 was conducted and what are the warning flags that we still need to take care of for the sustained and majestic survival of our national animal.

Dr Yadvendradev Jhala from Wildlife Institute of India attending to a tiger.

Tiger Census 2018: How was it conducted?

Back in 2006, tiger experts from India decided on a certain process to conduct a thorough tiger survey and submitted the methodology to the Tiger Task Force which was edited by Dr Sunita Narayan, a renowned Indian environmentalist and political activist who has been with the Centre for Science and Environment (CSE) since 1982 and is currently the director-general.

“She had it peer-reviewed through putting it up on the internet and inviting all International experts and it was approved that this one of the best ways of counting tigers at the national scale,” says Dr Jhala.

The methodology was then reviewed by four international peers in 2006 appointed by the International Union for Conservation of Nature (IUCN).

Dr Jhala explained that the tiger census works as a three-phase sampling process:

Phase 1: Frontline staff of state forest departments of 21 potential tiger-bearing states were trained to collect the Phase I data in a digital format on the M-STrIPES mobile application.
Phase 2: Remotely sensed spatial and attribute covariates – Distribution and abundance of wildlife are likely to be determined by habitat characteristics and anthropogenic impacts.
Phase 3: Camera trap based Capture-Mark-Recapture – Camera trap surveys are a well-established methodology.

(Photo: Status of Tigers in India 2018 summary report)

In the first phase, forest guards in the 20 states of India with tigers survey 400,000 sq km of forested landscape. Each guard covers around about 15 sq kms, and looks for all kinds of animal signs — including tigers, leopards, sloth bear, elephants and rhinos.

The forest guard then records either seeing the animal or their signs — mass, faecal matter or dung — through a mobile app known as M-STrIPES (Monitoring System for tigers – intensive protection and ecological status).

“The M-STrIPES app records GPS on its own and plots the track the forest guard has taken and every time he finds a sign, he takes a photograph of the sign and it is geotagged,” he says.

Thus, because of the geotagging system, one can get the location of the photograph along with the track the forester has taken. This is not some data that can be faked.

“So by mapping these animal signs across India, we know where which animal is found. We get a map of tiger distribution across India,” says Jhala.

Tiger distribution across India: Phase 1 results (Photo: Status of Tigers in India 2018 summary report)

Since 2006, the wildlife experts divided India into 100 sq km grids, which are fixed forever. If a tiger sign was spotted in any single grid, it was considered that the grid and the forest within it were occupied by tigers.

“This is where we need to estimate our tiger numbers — the population in that grid. So, we go out and put camera traps in the grids where tiger signs have been found. And we record photographs of tigers and all other animals which pass in front of our cameras,” Jhala explains.

These cameras are remote cameras, which are heat and motion-sensitive. Any animal which is warmer than the environment would be photographed if they are moving in front of the camera.

The team ended up with 3.5 crore wildlife images and used an artificial intelligence software called CaTRAT (Camera Trap data Repository and Analysis Tool) which uses neural network and image recognition, to classify them into individual species. There were around 76,000 photos of tigers.

Camera Trap locations across India (Photo: Status of Tigers in India 2018 summary report)

“Now, every tiger has a unique striped pattern. So you can fingerprint tigers by looking at their stripes. But inspecting 76,000 pictures would take us years and of course would also be prone to a lot of human error,” says Jhala.

Then the team used their next big software — Extract Compare. This allowed the wildlife experts to ‘fingerprint’ tigers and identify individual tigers by their stripe patterns by comparing images in the database

“So once we have our individual tigers identified, we count them, and we come up with a minimum number of tigers,” explains Jhala.

The 2018 tiger census was quite a big upgrade from the previous three cycles as it was undertaken using the best available science, technology and analytical tools. The M-STrIPES app, CaTRAT software and the Extract Compare programs made this tiger census the most accurate in history.

Step-by-step process of identifying tigers (Photo: Status of Tigers in India 2018 summary report)

How does one estimate the number of tigers who are never photographed?

This is not where the tiger census ends. Not all tigers come in front of the cameras but their numbers would need to be estimated as well.

“So there are statistical models known as mockery capture estimates, which are used to estimate that hidden population based on how often a tiger gets captured on a camera. It determines the probability of detection and gives us a population number which likely did not come in front of the cameras,” explains Jhala.

So ultimately, a population estimation of tigers is created by combining the two types of data – the tigers photographed and identified and the non-photographed ones whose numbers are estimated using software.

Forest guards tracking tigers in the Sunderbans using boats for the Tiger Census 2018

Tiger Census 2018: Data summary from the report

  • The survey covered 381,400 km of forested habitats in 20 tiger-occupied states of India
  • A foot survey of 522,996 km was done for carnivore signs and prey abundance estimation
  • In these forests, 317,958 habitat plots were sampled for vegetation, human impacts and prey dung
  • Camera traps were deployed at 26,838 locations
  • These cameras resulted in 34,858,623 photographs of wildlife of which 76,651 were of tigers and 51,777 were of leopards
  • The total area sampled by camera traps was 121,337 km
  • The total effort invested in the survey was 593,882 man-days
  • The report states that this is the world’s largest effort invested in any wildlife survey till date, on all of the above criteria
  • A total of 2,461 individual tigers (more than a year old) were photo-captured
  • The overall tiger population in India was estimated at 2,967 (SE range 2,603 to 3,346)
  • Out of this number, 83% were actually camera-trapped individual tigers and 87% were accounted for by camera-trap based capture-mark-recapture and remaining 13% estimated through covariate based models

33% increase in tiger population: Is this sharp increase only a result of better survey methods?

“As I told you, the grids are fixed since 2006 and they don’t shift. So the 400,000 square kilometres of forest which I’m talking about remains constant across all the four assessments of tiger populations that we are considering,” says Jhala.

Every grid of possible tiger habitation was assessed using either camera tracks or science surveys or both.

But the larger number of camera traps used for the 2018 tiger census since the last time is not why the numbers increased, explains Jhala. Rather, the estimates are more precise.

“The 30% increase, which you’re talking about is actually a 6% annual increase in tiger numbers. It’s like a compounded interest you know, so every time you put money in the bank, every year the rate of interest remains the same, but your money gets larger exponentially. And so in the case of any animal population which is growing, the growth rate is exponential,” Jhala explains.

Wildlife Institute of India scientist and a coordinator for the 2018 tiger census — Dr Yadvendradev Jhala

If a tiger died during the census would it be counted?

“There is no way of knowing this. It is an estimate, you cannot keep account of every individual tiger. It’s a snapshot taken in one and a half years across the country. So animals which are born, animals which died during that period are not accounted for,” explains Jhala.

Thus, if a tiger died in the forest or new tigers were born and added to the population during the survey period, there is no way of knowing the exact figures. The tiger census is based on the best possible estimates.

Understanding the male-female ratio among India’s tiger population can help us better estimate the species health and plan better conservation strategies. Jhala says that the gender balance details will be given in the final report of the Tiger Census 2018.

What has led to a decline in tiger population and even extinction in smaller areas?

Even though the overall number of tigers in India has increased, smaller populations of India’s national animal have gone extinct in certain corridors between major tiger habitations.

As per the report, tigers were not recorded in Buxa, Dampa and Palamau tiger reserves. These tiger reserves had poor tiger status in earlier assessments as well.

“There are many factors for the decline in tiger population in certain pockets of India — poaching is one of them, the second is removal of prey bas, and the third is loss of habitat,” says Jhala.

The Sunderbans are a critical habitat for the Bengal Tiger but it is rapidly sinking because of climate change. However, as Jhala says, there is nothing being done to safeguard the tiger population there.

Why irresponsible tiger tourism needs to go from India

“Currently, the model of tiger tourism in India is based on tourism, not on ecotourism. So the revenue which comes out of tourism is not shared with the local people there,” says Jhala.

“The second thing is, there’s something known as tourist-carrying capacity of a location. This needs to be computed in a proper manner, so that the experience of the tourists is of the highest standard and also leads to the least harassment to wildlife,” he adds.

He says that this is what he believes to be responsible tourism.

To understand the 2018 Tiger Census better and get an even deeper glimpse to one of the largest wildlife surveys conducted in the world, you can check out the National Geographic documentary ‘Counting Tigers’, which premieres on August 7 at 8 pm.

Read: Only 6 sub-species of tigers left: Here’s why they are going extinct

Read: Bengal tiger could go extinct as Sundarban habitats entirely vanish by 2070 because of climate change

Read: India’s first female wildlife biologist and ‘Tiger Princess’ Latika Nath on breaking India’s animal conservation barriers

Read: Tiger survival may depend upon urbanisation: Study

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