Counter stripe: Why are our big cats changing colour?

The black tiger is the least unusual of these anomalies. There have been records of sightings in Odisha dating to the 1700s, and the first recorded black-tiger pelt was seized from poachers in the 1990s. The gold tiger and the black wolf are rarer.

But in all three cases, a rising incidence is being linked to (say it with us) disruptions to ecosystems caused by human activity.

In India, the three types of unusual sightings have been reported in Odisha, Assam and Madhya Pradesh respectively, confirmed by researchers from the National Centre for Biological Sciences (NCBS), Bengaluru, and Wildlife Institute of India (WII), Dehradun.

Let’s take them one at a time.

The black tiger

Odisha’s Similipal National Park is home to the world’s only population of pseudo-melanistic tigers in the wild. These mutant big cats aren’t entirely black, but retain some of their original colouring.

In 2021, researchers at NCBS identified the genetic mutation that causes this anomaly.

“We know it’s a recessive trait, which means that any tiger presenting as pseudo-melanistic has received two copies of the gene, one each from the father and mother,” says Uma Ramakrishnan, a molecular ecologist with NCBS.

Now, likely as a result of isolation, the number of such tigers is rising rapidly.

In 2014, one dominant male out of Similipal’s six tigers was pseudo-melanistic, says Susanta Nanda, principal chief conservator of forests and chief wildlife warden of Odisha. “By 2018-19, a generation later, that number had grown to three of 12 tigers. Now, in 2023-24, 16 of the reserve’s 27 tigers as pseudo-melanistic.”

Ramakrishnan and her team studied non-invasive DNA samples such as scat. “The frequency of occurrence of this gene mutation in the Similipal population is rather high,” she says. “This could be because Similipal’s is a small and isolated population. It doesn’t have immigration or emigration with other reserves, and this could indicate inbreeding.”

A dedicated study would be needed to confirm this. For now, Nanda says there is a plan to supplement the population with two female tigers from Maharashtra or Madhya Pradesh, in a plan approved by the National Tiger Conservation Authority (NTCA), to enhance genetic diversity.

The state government, meanwhile, intends to cash in, with a safari dedicated to spotting the mutant big cats.

A golden tiger

Assam’s lone golden tiger was first photographed at Kaziranga National Park in 2019 by wildlife photographer Mayuresh Hendre.

Ramakrishnan of NCBS and her team have been conducting field work and research ever since, but have not yet found the mutation that causes this variation in the samples collected from Kaziranga. (The mutation was identified in a captive population.)

The colour and possible mutation aren’t what is worrying ecologists, though. It is the idea that such changes, if found across individuals, could indicate a deeper shift.

These kinds of changes could imply that recessive traits are becoming more common, possibly as a result of fragmentation of habitat, Ramakrishnan says.

Fragmentation is when a once-large population is split into isolated clusters, which could lead to inbreeding and a shrunken and eventually weakened gene pool. “Fragmentation is of relevance to conservation. If it is at play here, then it is something we should be cognisant of.”

Black wolves

These have been worrying sightings, by all accounts. Because there should be no black wolves in India.

Wildlife biologists Amolkumar Lokhande and Sameer Bajaru photographed India’s first documented black wolf in 2012, in Solapur, Maharashtra. Twelve years later, in April, Rupesh Kukade, a naturalist turned travel entrepreneur, and his team, photographed three others at the Panna National Park in Madhya Pradesh.

“India doesn’t have black wolves,” says Bilal Habib, a large-carnivore ecologist with WII. “Research in the US has shown that they only emerge because of a mutation inherited as a result of cross-breeding with feral or free-ranging dogs. Such cross-breeding happens when the density of the wolf population is low.”

It is worth noting, here, that the Indian grey wolf (Canis lupus pallipes) has retained its distinctiveness across millions of years. “Our grey wolves are among the most ancient and most evolutionarily distinct in the world,” Habib says.

This distinctiveness remained intact even as numbers of the protected species fell (there were as few as 3,100 individuals left in the wild in India, according to a 2022 estimate by WII).

There was so much to separate the wolves and dogs that it was considered improbable that they would breed.

“However, in the last couple of years, they have started to do so,” Habib says. “In India, this kind of cross-breeding is likely occurring in low-density fringes where small wolf populations are sharing their habitats with human populations.”

The next step, Habib says, would be to study where the black wolves are emerging, and ascertain whether these are isolated events or a trend that could disperse these genes to other populations. If it’s the latter, it could present a serious threat.

Studies and gene pools, of course, represent merely a corner of the landscape. As such research continues, it may also help to honestly reassess the way we talk about habitats.

When we speak of the number of species “left in the wild”, for instance, it might help to admit that the term is at least a bit misleading. The wilds aren’t entirely wild. They are isolated pockets, encroached upon, under threat, and often with roads cutting through them.

Each of these factors herds the animals further, altering their habits. It is this that is starting to show in gene pools.

And, as Ramakrishnan points out, colour may only be the most visible effect of a far deeper shift we have not yet begun to see.