Wildlife & Biodiversity

Can unmarked individuals of a species inhabiting rugged terrain be estimated? Study on Asiatic Black Bears shows how

The model can be replicated in mountainous landscapes with minimal sampling bias, ease of sampling and robust density estimation, the researchers say

By Rajat Ghai
Published: Thursday 14 July 2022

Asiatic black bears caught on camera trap in Daranghati Wildlife Santuary, Himachal Pradesh. Photo: Wildlife Institute of India Asiatic black bears caught on camera trap in Daranghati Wildlife Santuary, Himachal Pradesh. Photo: Wildlife Institute of India 

Scientists from the Wildlife Institute of India, Dehradun and the Himachal Pradesh forest department have calculated the density and population of Asiatic black bears in two Protected Areas (PAs) of Himachal Pradesh without identifying individual animals through hair samples or camera trap images.

They did this using a relatively new statistical model known as the Spatial Presence-Absence Model. They used camera traps like in the traditional Spatial Capture-Recapture Model. However, unlike it, they did not have to do two sessions of camera trapping.

“The first session of camera trapping in the capture-recapture model is used for identifying individuals through various characteristics. Then, a second round of camera trapping is done to confirm whether it is the same individual or a different one,” Ankita Bhattacharya, one of the lead authors of the study from WII, told Down To Earth.

Uniquely identifiable characteristics and features include stripes in tigers and rosettes in leopards and jaguars. Each individual has a unique pattern.

Asiatic black bears too have a white ‘V’ mark on the chest, which is why they are called ‘Moon bears’. But the pattern is visible only when the animal is in an erect position on its hind legs. This makes it difficult to identify Asiatic black bears through sampling methodologies such as camera trapping and direct sightings.

But the WII and forest department researchers did not have to do this. This is because the criteria for the presence-absence model is different. “One thing that this model requires to calculate the density and population is the number of captures in a camera trap. Another is called the movement parameter,” Bhattacharya said.

“Our traps made multiple captures of bears or other wildlife every day. We considered 24 hours as a single capture. This means that within that 24-hour interval, whether we got one or five captures of a bear, we considered it to be one detection,” she said.

So, if there were five captures in a day, the researchers did not consider them as five bears. Thus, in a 35-day session, if there were 30 days of bear capture, the researchers considered it likewise (30 captures).

The movement parameter means how many black bears can be seen in the buffer of a particular camera trap. “We already knew the usual home range of an Asiatic Black Bear. Using that information, we then deduced how many bears were moving within a fixed distance of a specific camera trap,” Bhattacharya said.

The scientists calculated that the population density of the bears for Darangati Wildlife Sanctuary,was 2.50 individuals per 100 sq km and the movement parameter was 2.25 km. 

The population density of Rupi Bhaba was 0.3 individuals per 100 sq km while the movement parameter was 2.86 km.

“Extrapolating the densities for the trapping areas produced abundance estimates of 11 individuals in Daranghati and two individuals in the Rupi Bhaba,” the researchers wrote.

A vulnerable animal

The researchers say the new method can be useful for gleaning information about this species given the immense challenges such a process usually involves.

The Asiatic black bear is one of eight extant (existent) species of ursids (the bear family) along with the American black bear, the sun bear, the spectacled bear, the brown bear, the polar bear, the sloth bear and the giant panda.

It is spread across Asia, from the Himalayas to the Russian Far East. It has been categorised as Vulnerable under the International Union for Conservation of Nature’s Red List of Threatened Species and is also listed under Appendix I of CITES and Schedule I of the Wildlife (Protection) Act, 1972.

The bears are found in 83 protected areas of India, spread across five states and 2 Union Territories in the Himalayas. They inhabit an altitudinal range of 1,200-3,300 metres, which may extend up to 4,300 metres. 

Also, it is one of the large carnivore species having negative interactions with humans in the Indian Himalayas, the researchers noted.

Till now, methods used to determine the population status of Asiatic black bears in India have been limited to questionnaires, sign surveys and genetic sampling using hair samples.

“This (our study) will provide a roadmap to manage and mitigate negative interactions in future, as well as monitor the demography, population trend and status of Asiatic black bears in the Indian Himalayas,” the researchers wrote.

Population estimation of Asiatic black bear in the Himalayan Region of India using camera traps was published July 10 in the BioOne journal. The authors are Ankita Bhattacharya, Nilanjan Chatterjee, Kunal Angrish, Dharamveer Meena, Bitapi C Sinha and Bilal Habib.

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