They also say that pugmarks are very hard to locate in regions where the land is hard or rocky, while finding suitable pugmarks in an area rich in tigers like the Sunderbans is near impossible because of the squashy mangrove conditions.
The WCS' Karanth says "the discrimination ability of the pugmark approach completely breaks down when data from different substrates is pooled in."
In an empirical study, the team took 32 tiger pugmark tracings from two different substrates of four captive tigers in the Mysore zoo. When shown to India's tiger census experts in a blind test, Karanth says, none of them was able to segregate the individuals, while the estimates of the total number of animals ranged from 8 to 23 individual tigers."
This test categorically "demonstrates that the present [pugmark] census-based paradigm does not work," said the investigating scientists. And "ecological data on tigers from field studies do not support the results generated from pugmark census."
Rajesh Gopal, an expert on herbivore biology and director of Project Tiger, New Delhi, defends the well-entrenched official method of tiger census, however. "As wildlife managers we have to be practical and pragmatic in adopting any method, and since the pugmark approach is in tune with the local conditions it will continue," he said, although he added that a panel of scientists is already working on refining the pugmark approach.
In a new three-year initiative costing about 1.1 million dollars (U.S.) in collaboration with the Wildlife Institute of India (WII), Dehradun, Project Tiger hopes to develop a GIS-based tiger habitat and population evaluation system which Gopal claims will be able to generate "ecologically audited maps for all tiger areas."
Officials at the Project Tiger Directorate in New Delhi say that the new system will indicate the trend of tiger population in the wild. It will also give an idea as to how tiger populations are spaced and what is the connectivity among them.
The new system will give an indication of the state of tiger habitatif it is increasing, decreasing, or stable. If it is decreasing, it will show which are the areas where the decrease has occurred and why.
The system is also expected to facilitate the study of the status of tigers' wild prey. It will devise specific monitoring and estimating protocols for obtaining reliable data from the field and will store this information so that it is readily accessible for effective field conservation, policy, and management decision-making.
Above all, it is hoped that the new system will help in disseminating the census, habitat evaluation, and monitoring protocols to field personnel through regional training workshops and manuals.
Lead researcher for this new initiative, Yadavendradev Jhala, a wildlife biologist from WII, admits that "tiger census conducted in India does not follow the protocol of sampling design or standard data quality control," but adds that some statistical models are being refined to identify individual tigers from their pugmarks. Once this is done, he said, it will "take the art to being a science."
Melvin Sunquist, an expert on tiger ecology at the Department of Wildlife Ecology and Conservation, University of Florida, Gainesville, said: "We need to get beyond the idea that we can get total counts of animals. It is one thing to count the number of cows in a pasture and be fairly certain that the number is accurate, but quite another to think that it is possible to count animals that are active at night and rarely seen We don't need total counts, we need accurate estimates. To get these estimates we can sample, just as political pollsters sample the general population, to estimate how many people will vote for a candidate."
Gopal says the new system will "serve as a monitoring tool for the tiger and its habitats" but will also serve to monitor the forests, their extent and the threats to them. "In effect, it would monitor the entire wilderness biodiversity resource for which the tiger serves as a flagship," he said.
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