SAZNEKHALI, India (Reuters) - Hundreds of forest guards and volunteers with firecrackers and nylon nets began scouring a swampy mangrove forest in India Wednesday for tigers, kicking off one of the world's largest censuses of the animal.

Wearing fiberglass protective vests, dozens of teams in speed boats moved across the riverine Sunderbans delta to determine if the tiger population had fallen in the region.

"The census is vital to ensure the survival of the endangered tiger as already four of eight sub-species in the world have become extinct," said Pradeep Vyas, field director of the Saznekhali tiger reserve, 60 miles south of Calcutta.

India, with around 4,000 tigers, has the world's largest tiger population and the Sunderbans ecosystem, divided between India and Bangladesh, is home to the largest numbers of tigers in a single region anywhere in the world.

While the number of tigers in the country has plunged from about 40,000 in 1947 due to poaching and killing by villagers, the drop in the Sunderbans delta has not been so alarming.

The tiger population in the Indian part of the delta fell to 271 in the 2001 census from 284 in 1999, and officials say this was due to natural deaths and not poaching or killing by people encroaching into the area.

Teams of eight to 10 people, equipped with firecrackers, nylon nets and rifles fanned out from Saznekhali to make plaster of Paris molds of tiger paw prints to try and determine the number of the cats.

These censuses can be very dangerous as many of the tigers are man-eating and there are also crocodiles in the sparsely populated Sunderbans.

Last year, Royal Bengal tigers in the area killed at least six villagers while in 1995, one forest ranger was killed in an attack by a big cat during a census.

"The census is sometimes scary because, while taking pug marks of tigers, we can see a tiger less than half a kilometer away. But it is also exciting," said Gopal Krishan, a forest guard with 17 years of experience in tiger counts.

Indian forest guards use plaster to cast a paw print of a Royal Bengal tiger, during a preparatory exercise for a tiger census at Sanzekhali, in the Sunderbans mangrove forest delta, Jan. 12, 2004. Hundreds of forest guards and volunteers with firecrackers and nylon nets began scouring a swampy mangrove forest in India on Wednesday for tigers, kicking off one of the world's largest censuses of the animal. (Jayanta Shaw/Reuters)