The birth of four cubs to Tadoba-born translocated tigress Zeenat in May has marked the first visible success of India's ambitious genetic rescue programme for tigers in Odisha's Similipal Tiger Reserve (STR).
The programme aims to strengthen the reserve's genetic diversity by introducing unrelated tigers from healthier populations elsewhere in the country. It seeks to address decades of isolation and inbreeding that have left Similipal's tigers genetically vulnerable.
Spread over 2,750 sq km, Similipal is home to 32 unique tigers and is the world’s only known landscape where a significant number of pseudo-melanistic (black) tigers occur naturally. While their striking appearance has made them globally famous, conservationists believe their unusually high numbers reflect the reserve's shrinking genetic diversity.
Why are Similipal's tigers genetically vulnerable?
Similipal's tigers became genetically vulnerable because the population remained isolated from other tiger landscapes for decades, preventing fresh genes from entering the reserve. As a result, the tigers became increasingly inbred.
The situation worsened during the early 2000s. From an estimated 45 tigers in 2006, the population crashed sharply, with only eight tigers photo-captured during the 2018 All India Tiger Estimate (AITE). Tiger density fell to about 1.02 tigers per 100 sq km, among the lowest for a major tiger habitat.
Improved protection and habitat management later helped tiger numbers recover. However, the rapid rise in pseudo-melanistic tigers raised fresh concerns. The All-Odisha Tiger Estimation (AOTE) 2023-24 recorded 13 black tigers in Similipal—nearly half the reserve's tiger population—highlighting the effects of prolonged genetic isolation.
Why are some Similipal tigers born black?
Pseudo-melanistic tigers are not a separate subspecies. They are Bengal tigers that inherit a rare recessive mutation in the Taqpep gene. A tiger develops the distinctive dark coat only if it inherits the mutated gene from both parents.
The first confirmed record of a pseudo-melanistic tiger from Similipal dates back to 1993, although they were first officially documented in 2007. Their numbers continued to rise over time before researchers identified the genetic mutation responsible for the unusual coat pattern.
What did the studies show?
Genetic studies published in 2021 confirmed that Similipal's tigers had unusually low genetic diversity and high levels of relatedness, providing the scientific basis for the genetic rescue programme.
Researchers led by senior molecular ecologist Prof Uma Ramakrishnan of the National Centre for Biological Sciences (NCBS), Bengaluru, collected genetic samples from 12 Similipal tigers in 2018 and 2019 and compared them with samples from 366 tigers across northwestern, central and southern India.
They assessed two key indicators of genetic health: heterozygosity, which measures genetic diversity, and relatedness, which measures how closely individuals are related. Higher heterozygosity and lower relatedness indicate healthier populations with less inbreeding.
Similipal's tigers showed low heterozygosity (0.28) and high relatedness (0.38), confirming low genetic diversity and significant inbreeding.
Computer simulations further suggested that the present population descended from a very small number of founding individuals, explaining both the concentration of the pseudo-melanistic gene and the reduced genetic variation.
Why was Tadoba chosen as the donor reserve?
The studies showed that central India's tiger populations possessed far greater genetic diversity than Similipal's. Among them, Tadoba-Andhari Tiger Reserve (TATR) in Maharashtra emerged as the best donor population because it had the highest genetic diversity and the lowest genetic load.These findings guided wildlife managers in selecting Tadoba as the source population for Similipal's genetic supplementation programme.
When was the genetic rescue programme rolled out?
The programme began in 2024. The original plan envisaged introducing six tigers—five females and one male—over five years. The National Tiger Conservation Authority (NTCA) approved the first phase involving two tigresses, Zeenat and Jamuna, both translocated from Tadoba.
What happened after Zeenat was released?
Zeenat did not settle inside Similipal after her release, forcing wildlife managers to rethink their translocation strategy.
After spending eight days in a soft-release enclosure, she was released on November 24, 2024. Instead of establishing a territory inside the reserve, she moved north through Jharkhand and later West Bengal. Such movements are common among translocated large carnivores as they explore unfamiliar landscapes and avoid resident animals.
Jamuna also initially moved towards the reserve boundary before eventually settling around the Kuldiha landscape. Zeenat, however, continued wandering without establishing a territory.
Wildlife authorities concluded that both tigresses instinctively avoided areas occupied by resident females. In the wild, young females usually establish territories adjoining their mother's home range, a behavioural anchor that was absent after translocation.
How did STR change its strategy?
STR shifted from direct release to a longer acclimatisation process that allowed Zeenat to adapt gradually before entering the wild.
After Zeenat was brought back from West Bengal following a 23-day operation, authorities built an eight-hectare enclosure with an adjoining four-hectare boma at Jamuna meadow in the reserve's core area. Natural prey species such as deer were periodically released into the enclosure so that she could hunt while remaining protected from resident females.
The enclosure also allowed the dominant male, T-12, to interact with her across the fence.
The revised strategy proved successful. Zeenat was returned to the enclosure on January 1, 2025, shifted to the larger enclosure about 40 days later, and had settled comfortably by April.
After she showed signs of being in heat, the enclosure gates were opened. She subsequently mated with another male in the core, marking a key milestone in the genetic rescue effort.
Why is the birth of Zeenat's cubs significant?
The four cubs provide the first indication that Similipal's genetic rescue programme may be achieving its objective of improving the reserve's genetic diversity.
The four-year-old tigress gave birth in May 2026, marking a major conservation milestone for Odisha. The birth increased the number of tiger cubs in Similipal from 12 to 16.
While it will take years to measure the programme's long-term genetic impact, the successful breeding of a translocated tigress is an encouraging early outcome.
What lies ahead for Similipal?
The immediate objective is to establish a genetically healthier tiger population in Similipal, while the long-term goal is to restore natural gene flow across eastern India's tiger landscapes.
The first phase of the genetic rescue programme is now complete. Based on the present prey base, officials estimate that Similipal alone can support about 75 adult tigers within the next five years. The wider Similipal landscape—including Kuldiha and Hadgarh Wildlife Sanctuaries and the connecting reserve forests of Rebana, Atei and Ranjagarh across Keonjhar, Dhenkanal and Jajpur districts—could support up to 200 tigers if managed as one interconnected landscape.
While translocating tigers from healthier populations is an immediate measure, experts say the long-term solution lies in restoring habitat connectivity and creating additional source populations so that tigers can once again disperse naturally across eastern India.