Decoding 'Capture and re-capture' method to monitor elephants in national parks

New Delhi, June 18: As highly social animals - like human beings - elephants rely on their bonds to navigate everyday life. Though India holds the largest population of Asian elephants surviving today, currently distribution and abundance of elephants have both dwindled drastically throughout its range due to habitat loss and poaching.

In spite of its conservation significance, elephant populations across the country continue to be monitored using methods and techniques that are not rooted strongly in the principles of modern wildlife science. Lack of rigorous data and reliable inputs on the population status of elephants have hampered their management across range countries.

A recent study carried out by scientists from Wildlife Conservation Society India (WCS India), in collaboration with the Forest Department, Assam, is paving the way for reliable estimation of Asian elephant populations.

The researchers highlight how systematically documented photographic identities of individual elephants, when combined with advanced spatial
capture-recapture models, present a reliable approach to estimate Asian elephant populations. This is the first study of its kind in the Northeast India region.

What is Capture-recapture method?

Capture-recapture is an advanced method that uses systematic tracking of individually identified animals to estimate population numbers while accounting for the possibility of missing animals during surveys.

"Our study pioneers the use of photographic spatial capture-recapture to estimate all segments of an Asian elephant population, including the largely solitary adult males and the herd-living adult females and younger elephants", said Dr. Goswami, a senior scientist at WCS India who leads the Asian elephant and Northeast India programs for the organisation.

"The approach also provides fascinating insights into fine-scale space use and movement of elephants in the dynamic floodplain ecosystem of Kaziranga National Park, our study site," he added.

The world renowned Kaziranga National Park is home to diverse and abundant assemblage of wild herbivores, including the largest population of the greater one-horned rhinoceros. This assemblage supports one of the highest densities of tigers worldwide.

Pilot project in Kaziranga National Park

"Kaziranga National Park is celebrated internationally for the success with which its rhino population has been revived and a variety of threatened species are protected," said co-author M K Yadava, IFS, who is Additional Principal Chief Conservator of Forests (Research Education and Working Plans), Assam.

"It is critical that populations of priority conservation species, such as Asian elephants, be reliably monitored in parks like Kaziranga for informed management decisions and to adaptively strengthen conservation efforts. It would greatly aid in understanding the increased human-elephant conflicts in the State. However, this is just a small beginning," he concluded.

Keeping a track on elephant movements

Periodic flooding of the Brahmaputra River that forms the northern boundary of Kaziranga National Park makes it necessary for wildlife to move between the park and habitats to its south.

"An exciting aspect of using spatial capture-recapture models is that it allowed us to not just estimate how many elephants are in the park, but also account for those elephants that may have moved in and out of the park from neighbouring habitats," said Dr. Divya Vasudev, a senior scientist and connectivity specialist who co-leads the Northeast India program for WCS India.

"Landscape-scale conservation is particularly important for wide-ranging species like the Asian elephant", added Dr. Goswami. "Conserving such species at large spatial scales hinges very critically on science-based policy, a clear long-term vision, and the ability to consider diverse challenges and opportunities that heterogenous landscapes present", concluded Dr. Goswami.