Wildlife specialists have for long faced challenges estimating the density of leopards in areas where some of the spotted cats are melanistic or black.
Experts from three organisations, one of them Assam-based Aaranyak, have come up with a system that helps in properly estimating the leopard population in areas sustaining a mix of rosette and melanistic individuals.
Rosettes are jagged black circular marks on the tawny coat of a leopard. Like the tiger’s stripes, the rosettes of each leopard are unique in shape and size, making the species identifiable individually.
But melanistic leopards — commonly called black leopards or black panthers or ghongs (Assamese) — have been difficult to estimate as their rosettes are invisible.
The Spatial Mark-Resight (SMR) models applied by the scientists of Aaranyak, Panthera and World Wide Fund for Nature-India have provided a way of counting the melanistic leopards too. The new model has been written about in the Animal Conservation journal.
U.S.-based Panthera is the only organisation in the world devoted exclusively to the conservation of the world’s 40 wild cat species and their ecosystems. Melanism has been documented in 14 of these species, including the leopard.
“When a population has only rosette leopard, estimating their population size becomes easy because all the individuals can be identified. Unlike rosette leopards, a black leopard can often not be reliably identified individually, although special cases exist. We are, therefore, unable to completely estimate population sizes of leopards, a metric that is very critical for their conservation,” Dipankar Lahkar, a tiger biologist with Aaranyak, said.
“This problem is acute in the tropical and subtropical moist forests of South and Southeast Asia where the frequency of melanistic leopards is high and leopards also face the greatest threat. No precise estimates of leopard population could thus be done in protected areas and non-protected areas in India except on some occasions,” he said.
M. Firoz Ahmed, the head of Aaranyak’s tiger research and conservation division, said the team used three years of camera trapping data between 2017 and 2019 obtained from Manas National Park to establish the SMR approach.
The population density of leopards in Manas is 3.37 per 100 sq km. In the study, about 22.6% images of the leopards were of the melanistic kind.
“In the SMR models, we then borrow the capture history of the rosette leopards and apply the information on the melanistic leopards to estimate the entire population size of leopards. This is a significant analytical development that can help assess the population of leopards across a great part of the species range from where population estimates are scant,” said Panthera’s Abhishek Harihar.
The SMR method is expected to make it easier to assess the population status of leopards for informed conservation measures by applying the conventional camera trapping field method.
It can also be widely applied for other species that exhibit similar colour variation in nature, the wild cat specialists said.