Indian tiger study earns its stripes as one of the world’s largest wildlife surveys

By Adam Millward
Published
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The latest “tiger census” to be carried out has not only showed positive signs that numbers of the world’s largest wild cat are on the up in India, but has also been recognized as the largest camera-trap wildlife survey ever conducted.

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The findings of the study which have now been formally published – as well as its successful record – are being reflected upon across India and beyond on 29 July, which marks International Tiger Day. 

A census to assess the number of Bengal tigers (Panthera tigris tigris) in India has been carried out every four years since 2006 by the National Tiger Conservation Authority (part of the Indian Government) and the Wildlife Institute of India. 

This has been done in collaboration with local forestry staff, NGOs, academics and international nature charities such as WWF, the largest environmental conservation organization. The scale of the 2018–19 census was the most ambitious to date.

To give you an idea of just how comprehensive it was, a team of more than 44,000 officials, working with 55 biologists over 15 months, are estimated to have worked an equivalent of 620,705 labour-days (just under 14.9 million hours) on the project from start to finish.

Study co-authors Dr Jhala Yadvendradev and Professor Qamar Qureshi with the official Guinness World Records certificate earned by the tiger census  

Camera traps are outdoor photographic devices equipped with motion sensors that are triggered to start recording when an animal passes by. 

They are now used as an unobtrusive method to observe wildlife in its natural habitat for all manner of zoological studies, particularly of species that are known for their elusiveness or that inhabit remote areas. 

Camera traps being calibrated in Kaziranga National Park in Assam, India  

For this record-setting survey, camera traps were placed strategically in 26,838 locations in 141 different sites across 20 states of India known to host tigers.

They were trained mainly on forest trails, dirt tracks and stream beds that these apex predators are known to frequent. 

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The effective area covered by all of these traps combined was 121,337 km2 (46,848 sq mi) – almost three times the size of Switzerland! 

It’s worth flagging that camera traps formed just one aspect of the latest assessment into the status of India’s tigers. 

In an earlier phase, on-the-ground foot surveys equating to a distance of 522,996 km (324,974 mi) – that’s equivalent to a trip to the Moon and halfway back – were carried out by local rangers across allocated "beats". 

The camera traps also captured a wealth of other wildlife, including grey langurs, water buffalo and sloth bears - some of which were more curious than others!  

The detailed observations from these transects were fed back via an app to the study coordinators in order to establish the prevalence of carnivores and their prey (through direct sightings and indirect indicators such as paw prints and dung), as well as reporting on the state of vegetation and signs of human disturbance that impact significantly on tigers’ habitat. 

Staff receive training in plant identification as part of the habitat inspection element of the survey  

By the end of the survey, just under 35 million photographs of wildlife had been snapped. Of these, 76,651 were of tigers and 51,777 photos were of leopards (Panthera pardus); the remainder were other fauna. 

The tiger census is also an opportunity to assess the status of another of India's big cats, leopards  

From these photos, a total of 2,461 tigers, deemed to be at least one year old, were identified using cutting-edge stripe-recognition software. (A tiger’s stripes, like our fingerprints, are unique to each individual making this counting method extremely reliable.) 

Young cubs were not included in the final tiger count

Extrapolating to factor in areas known to host tigers but where camera traps were not deployed, the researchers estimate that India’s total tiger population is now somewhere in the region of 2,927 – up almost a third from the 2014 census. 

The “lion’s share” of these (1,492) inhabit three Indian states: Madhya Pradesh in the central region (526), Karnataka in the south-west (524) and Uttarakhand in the north (442). 

The cameras snapped a few more unusual specimens, including this partly leucistic tiger and a melanistic leopard (aka black panther)

While the uptick is welcome news, some conservationists have advised caution, highlighting that the apparent sharp rise in numbers may partly be the result of improved surveying methods rather than purely down to a boom in the tiger population. 

The study also flagged that there could be no resting on laurels when it came to conservation, calling out a number of areas that demand attention. 

These include improving (and increasing) corridors between small pockets of tiger territory, continuing the ongoing fight against poachers and restoring habitat to encourage the return of herbivores that form a crucial part of the big cats’ diet. 

One of the lead authors of the study published off the back of the survey, Dr Jhala Yadvendradev of the Wildlife Institute of India, said: “India has achieved a difficult conservation target of recovering its wild tigers against the odds of poaching and pressing needs of 1.3 billion people."

Dr Jhala Yadvendradev of the Wildlife Institute of India collaring a tiger in order to gain a better understanding of these big cats' movements  

“The recognition by Guinness World Records of India’s effort in documenting this achievement has given this programme a renewed impetus. Record camera-trapping was possible due to the hard work by field staff and the joint effort of wildlife managers and scientists.”