Marshall's documentary, Queen of the Elephants, which will be shown on television in the United States in March and here in the autumn, features Parbati Barua, a stunning Indian in her thirties who has devoted her life to the welfare of pachyderms. Her father, Lalji Barua, Prince of Gauripur, held the concession for catching wild elephants in West Bengal and Assam for 50 years; in particular, he practised the technique known as mela shikar, lassoing wild animals from the backs of tame ones. Catching elephants is now a thing of the past, but Parbati, growing up among them, developed an astonishing affinity with these animals.
The film is part travelogue, part history of the Indian elephant; but it also touches on the problem of conflict between animals and men, which is becoming acute as the human population inexorably grows. Just as in other parts of India men and tigers now clash on the fringes of the jungle - with a consequent increase in man-eating - so, in West Bengal, men and elephants are being forced into confrontation by the progressive diminution of the great beasts' range.
For 4,000 years Indians have revered elephants and enjoyed a mutually beneficial relationship with them. Ganesh, the elephant-headed god, is one of the principal Hindu deities. Yet now competition for living space is forcing both parties to adopt hostile attitudes towards former allies. With the forest shrinking and the elephant population growing, the animals - each of which eats up to 600lb of green fodder every 24 hours - have only two alternatives: to stay in the jungle and starve, or come out on to human territory.
The problem is most serious in the tea gardens that cover thousands of acres of the Himalayan foothills and are now the front line in the battle. Luckily, elephants do not like tea itself, and inflict little damage on mature bushes: as Peter Leggatt, chairman of the Goodricke group, puts it, 'they tiptoe through the tea with extraordinary delicacy'. On the other hand, they cause havoc among the ancillary fixtures and property of the tea estates.
Any innovation close to their regular routes seems either to fascinate or annoy them. They rip the roofs off leaf-weighing sheds, and knock down any new construction to which they take exception. They also pull down electric fences designed to keep them out, trample and browse among vegetable crops planted for workers, and tear branches off carefully planted shade trees, either for food or for use as fly-whisks.
Worse, they are now killing humans at the rate of at least 200 a year. In areas equipped with electricity, people have some protection, in that they can switch on lights to scare off the nocturnal raiders; but in places where there is no power, they are almost defenceless.
In the old days human deaths were generally the result of chance encounters at night, when elephants reacted violently out of surprise or fright. Yet now more and more Indians are being killed deliberately: stress is apparently turning elephants into murderers who stalk humans with premeditated intent. Another unpleasant change is that they have taken to dismembering their victims: holding down the body with one foot or knee, they pull off the limbs with their trunks, and often carry away an arm or a leg into the forest. This has given rise to rumours that elephants have turned carnivore - an idea for which there is no basis of truth, but one which naturally increases fear among potential victims.
Because the animals are protected by law, none may be shot without the issue of a special licence. Damage to property alone is not a sufficient crime: any individual must have killed at least 12 humans before a permit for its execution can be issued. Even then, the legal process is too slow to be effective: a licence has to come from Calcutta, and is valid for only three months. By the time an official marksman reaches the area, the criminal has usually pushed off into the safety of the jungle.
Another difficulty is that age-old sympathy for elephants still runs strongly in many villages. When the sharpshooter arrives, armed with his permit and heavy rifle, and the killer has been tracked down, local people - in spite of their fear - plead for Ganesh Baba to be spared.
Yet attitudes are changing, and some humans are taking retaliation into their own hands. Because elephants love salt, molasses and, above all, the local rice beer called haria, for which they will break into houses, they are easy to poison, and many now die in agony after taking bait. But in some extraordinary way they seem to be able to identify particular human enemies.
In one area of Assam, where seven or eight members of a herd had been poisoned, the survivors hit back vigorously and killed more than 20 people. Simplistic as it may be to attribute human motives to animals, this looked uncannily like revenge.
Again, while Marshall was filming, a woman was killed near by, and in the local chaikhana, or tea house, the word was that she had had retribution coming to her, since she had been abusing Ganesh Baba. Certainly her killer seemed to pick her out: as she ran out of her house, carrying a two-year-old child, the elephant carefully used its trunk to remove the baby from her arms, and then crushed her to death.
From her base in Gauripur, Parbati now travels the country with two or three trained elephants, moving in response to summons from wildlife departments, timber organisations and tea-planters. One of her tasks is to drive leopards out of tea gardens. Like urban foxes in Britain, leopards frequent areas of human habitation, and often take up temporary residence among tea bushes. If this happens, and a human is attacked, panic may set in; and until the area is cleared by a trained elephant, nobody will return to work.
Parbati is doing as much as any human can to contain the situation; but it is clear that large-scale innovations will be needed if conflict is not to become intolerable. One idea is for the creation of green corridors, along which elephants could move from one area of forest to another. Ironically, the tea estates, which now cover much of the animals' original habitat, may themselves hold a solution.
With their shade trees, the gardens provide at least shelter, and comparative peace from hostile villagers and farmers. Corridors could be formed by linking the substantial ancillary areas on which trees such as eucalyptus and acacia are grown to provide firewood for cooking and heating.
So far this ambitious scheme is merely a dream; but, in Marshall's words, 'it is clear that major action will have to be taken. Otherwise, humans will have sold out their oldest ally.'