Elsewhere in the world, tigers seldom kill people.

But in Sundarbans the tigers are utterly different.

“Among these islands, it is in many places dangerous to land,” the French explorer François Bernier wrote in 1666: “For it constantly happens that one person or another falls prey to tigers. These ferocious animals are very apt, it is said, to enter the boat itself, while the people are asleep, and to carry away some victim, who, if we are to believe the boatmen of the country, happens to be the stoutest and fattest of the party.”

Here healthy tigers have hunted humans for centuries. Genetically these tigers belong to the same race as the others found throughout the Indian subcontinent, the Royal Bengal, the second-largest tiger on earth (the Siberian is largest), with a flame-colored coat. Yet the Sundarbans tigers behave like no other tigers in the world; in fact, no other predator of any species so aggressively seeks out our kind. “Nowhere else in the world is man so actively hunted out,” said one wildlife consultant who has visited Sundarbans many times. “You can feel it: someone is trying to kill you.” The idea floats uneasily in the modern mind.

Why do these tigers hunt people?

The German biologist Hubert Hendrichs suggested that their ferocity might be linked to the saline water they drink. In 1971 he carried out a three-month study on the Bangladeshi side of Sundarbans. He compared the relative salinity of the water with the locations of known tiger attacks. His data correlated the most frequent attack sites with areas having the saltiest water.

Virtually no fresh water is available in Sundarbans except dug rainwater ponds. The tides of the Bay of Bengal flush through all the rivers; in certain areas the water is 1.5 per cent salt. Drinking water so salty may cause liver and kidney damage, Hendrichs suggested, making the tigers irritable. Before he could test this hypothesis, his study was interrupted by Bangladesh’s war of independence, and he has never returned.

No one since has proved or disproved his idea. Possibly, some have said, Sundarbans tigers learned to eat human flesh because it was brought to them, like an offering, from the holy river Ganges. Before its tributaries were dammed by the Farakka Barrage, this river nourished Sundarbans, and with its waters came the corpses of the dead who had been incompletely cremated at Calcutta’s burning ghats. The tigers could have acquired their taste for our flesh from scavenging.

S Dillon Ripley, the former secretary of the Smithsonian Institution, theorised that Sundarbans tigers may have learned from fishermen to associate people with food. An ancient fishing method in Sundarbans is to string your net across a narrow creek and wait for the fish to become caught in it as the tide recedes. Perhaps, Ripley suggested, the tigers learned to raid the fishermen’s nets, and so learned to seek out the fishermen and their boats. Perhaps the fishy smell also attracts the tigers.

Still others have noted that in the sucking ooze of the swamps tigers might have difficulty catching their normal prey – wild boar, chital, rhesus macaques, monitor lizards, junglefowl – so they supplement their diet with people.

In Sundarbans a human provides one of the larger food items available to a tiger

An adult male wild boar or a chital doe might weigh a bit over a hundred pounds, and in taking it the tiger faces grave risks. To attack a big animal is not easy when you kill with your open mouth. A fighting boar slashes with sharp tusks, a struggling chital thrashes with antlers and hooves. The average adult male human in Sundarbans might weigh 130 pounds. Relatively large, slow-moving, clumsy, and, without guns virtually harmless, people are easy and abundant prey.

One wonders why Sundarbans tigers do not eat people more often than they do. (One Indian expert calculated that if people comprised a major item of the tigers’ diet, then Sundarbans tigers would kill 24,090 people every year.) The wonder is not that tigers eat people in Sundarbans; the wonder is that tigers so infrequently eat them elsewhere.

But this is only one of the mysteries, for tigers are very difficult animals to study. They are secretive, and often difficult to find, even a glimpse. In his long career photographing Indian wildlife, the great naturalist EP Gee never got a shot of a wild tiger.

A tiger’s range can be enormous: in Nepal, Melvin Sunquist found that males established territories of twenty-three to twenty-seven square miles, and females six to eight square miles; in Siberia, where food is scarcer, a tiger’s territory may stretch for 1,544 square miles.

Tigers are mostly solitary

They will associate with others of their kind – often at a kill – and a tigress may remain with her one to four cubs for two years. Courting pairs travel together for several days. Still, a scientist usually is able to observe only one tiger at a time rather than the herds or flocks or troops of animals of other species.

Tigers live by stealth. Because they are stalk-and-ambush hunters, it is extraordinarily difficult to see one make a natural kill; you must be as stealthy as a tiger to avoid scaring away the prey, and you must be warier than the prey to see the tiger.

Most of what Western researchers know about these animals derives from two long-term projects. The first was George Schaller’s fourteen-month study of deer and their predators at Kanha National Park in central India from 1963 to 1965.

He learned to recognise eleven individual adult tigers on sight, and he spent 119 hours watching them. He examined their kills and analyzed their droppings. He listened to their voices. The book presenting his results, The Deer and the Tiger, remains a landmark.

A second and larger study, financed by the Smithsonian Institution and the World Wildlife Fund, began in November 1973 at Nepal’s Royal Chitwan National Park, and still continues. John Seidensticker and K. M. Tamang developed ways to capture and immobilize tigers and outfit them with radio collars to track their movements. Their work allowed scientists for the first time to follow several tigers at once, to monitor their long-term health and growth, and to map their ranges.

But still science knows relatively little about tigers. About tigers in Sundarbans, science knows almost nothing. They are a mystery – the mystery that drew me to Sundarbans and into the spell of the tiger.

Excerpted with permission from Spell of the Tiger: The Man-Eaters of Sundarbans, SY Montgomery, Aleph Book Company.