THE FIRST all-India tiger census in 1972 was designed by then senior research officer Saroj Raj Choudhury and his trainees at the Forest Research Institute in Dehra Dun. The method used the hind pugs left by a tiger. No matter how the tiger walks, its hind pugs are usually clear. The hind pug is smaller than the front pug and presents features that can help distinguish not only between male and female tigers, but also the left and right paws.

The pug of a tiger cub and that of an adult leopard are almost equal in size and never more than 9 cm long. In the refined technique (Indian Forester, Vol. 116, No. 3), the strides are measured -- there are longer strides in a leopard's track because an adult leopard has a longer body and higher limbs than a tiger cub.

To distinguish between male and female tigers, a technique formulated in 1979 by H S Panwar, in which the male tiger's hind pug is taken to fit into an almost square frame, while the female's fits into a rectangular frame, is used. In a refinement of this technique, a difference of upto 1.5 cm between the length and width of the pug is allowed in the square against which male pugs are measured (Indian Forester, Vol. 117, No. 1).

The census is taken over 6-8 days so as to allow pugs to be double-checked. Pugs seen in one area are compared with those in adjacent areas before final figures of leopards, tigers, pug sizes, strides and movement areas are catalogued and mapped. To meet these requirements, pugs on the ground are so translated that the transcriptions are true, portable and storable. The accurate features of the pug are drawn on a "tiger tracer", a glass sheet measuring 30 x 25 cm, which is placed on it.

Plaster-casts of the pugs are also necessary because a tiger census is a large-scale operation and not everyone follows the same standards while tracing pugs. In Similipal for example, there are 45 census units involving more than 150 persons, 253 census routes and nearly 3,700 PIPs (pug impression pads) scattered over a total route length of 1,240 km. A pug impression pad is fine soil placed over roads, footpaths and animal tracks so that the tigers will leave their pugs on it.

Wildlife students often wonder how we can be sure that a tiger hasn't been overlooked. Each Project Tiger area represents a different biome, which is a large, naturally occurring community of flora and fauna, adapted to the particular conditions in which they occur. In difficult and inaccessible terrains, it is quite possible that we may miss one or two tigers. Recounting a tiger, however, is impossible because of the extremely rigorous process of elimination involved in a census.

No single census procedure can be applied to all tiger reserves. In Similipal, water is not a limiting factor, but as PIPs are used, they must be laid when the forest is not open. Hence, December is the census month in Similipal, though in most other areas, it takes place in the summer. Counting pugs is the most reliable and economical method of tiger census. Field-data obtained through counting pugs can be preserved as tracings or plaster casts for study, comparison and reference. The method also allows ample scope for refinement. L A K Singh is the deputy vice chairman of Project Tiger at Similipal Tiger Reserve in Orissa.