New Delhi, June 17: Chronic stress, potentially triggered by encounters with humans and related human activities, appears to be preventing tigers reintroduced in the Sariska tiger reserve in Rajasthan from reproducing adequately, government wildlife biologists have said.
The scientists at the Wildlife Institute of India (WII), Dehra Dun, and other institutions have documented high levels of glucocorticosteroid residues in faecal samples of Sariska tigers that they say could explain their low breeding success since their reintroduction in 2008.
Their study, just published in the scientific journal PLOS One, is the first from India to examine how the presence of humans, villages and vehicular traffic can affect the physiology of tigers and even interfere with their attempts to breed.
"We're trying to understand how exactly human-related disturbances can affect the biology of tigers," Krishnamurthy Ramesh, a conservation biologist who specialises in landscape ecology studies at the WII and a member of the research team, told The Telegraph.
The Sariska tiger reserve area - inhabited by about 100,000 people and their estimated 190,000 livestock scattered across 32 villages located within the core area of the reserve - has long been viewed as a hostile place for tigers. Sariska had lost all its tigers about a decade ago, conservation scientists suspect, through a combination of poaching and growing pressure from human activities.
But the Rajasthan forest department, supported by the National Tiger Conservation Authority (NTCA) and the WII, reintroduced tigers in the Sariska reserve in 2008, initially bringing three females and two males from Ranthambore tiger reserve and adding a few more over the next three years. A year later, Madhya Pradesh similarly introduced tigers in Panna, another reserve that had also lost its tigers.
"We see a dramatic difference in the breeding rates between Panna and Sariska," Ramesh said.
Sariska received nine tigers between 2008 and 2011, and has only managed to increase its population size to 13 tigers. But Panna, which began with three animals - one male and two females - and received three more females later, has increased its tiger population to over 35.
For their study, scientists from the WII, the Centre for Cellular and Molecular Biology, Hyderabad, and the University of Pretoria, South Africa, examined faecal samples of Sariska tigers and used radio collars to track tiger movements across the reserve for two years.
They observed that tigers in Sariska are exposed to more humans, more traffic, more roads and more livestock than tigers in Panna. "Our findings challenge the claim that humans can co-exist with tigers in their core reserve areas," Govindhaswamy Umapathy, a team member at the CCMB's Laboratory for the Conservation of Endangered Species, said. "Encounters with humans and livestock, and even the need to cross roads with traffic contribute to stress in the animals."
The terrain in Panna provides a large number of relatively isolated and secure spots such as escarpments that allow tigers to keep away from humans. "Animals need a secure place to successfully breed - when corticosteroid levels rise, reproductive hormones are suppressed, thus affecting breeding," Ramesh said.
But Sariska lacks areas that can serve as secure spots. One tigress took nearly four years to find an undisturbed 3sqkm area within her home range to litter and raise her cubs. The scientists say it may be necessary to stop all human activities in certain pockets of the reserve.
The WII-CCMB scientists have recommended that eight villages within the core area should be relocated, water holes used by the tigers should be moved away from tarmac roads, and the flow of vehicular traffic be curbed within the reserve.
The relocation of the eight villages will make available about 300sqkm of area available for tiger breeding.
