Over the weeks that followed the filming of the feeding vampires, we began to view these bats very differently and even respect them in a curious way. The bat control group showed us several roosts to choose from for filming the next sequence, the vampires 'at home'. One was a spectacular limestone cave hung with stalactites and with deep chimneys in the ceiling. It was in the dark recesses of these chimneys that the vampires lived, hanging upside down from the rock in dense clusters. Feeding on blood may seem a squalid habit but the vampire is, like most bats, a sociable animal and keeps itself scrupulously clean, a large proportion of its time being spent in grooming, using the sharp claws of the feet for combing the fine fur. The fur is so fine that the Inca emperor Atahualpa in the sixteenth century is said to have had a cloak made solely from the skins of vampires. Even when excreting, the vampire meticulously pushes its body away from the cave wall in order not to soil itself. That was the unpleasant part for us standing underneath in a constant rain of bat excrement, which collected in pools on the cave floor. Unlike the guano of other bats, that of vampire is black and smells strongly of ammonia: two sure signs of a vampire roost. Not much, you would think, could live in the black pools that looked like sticky treacle, but we found several tiny creatures there.

Although the vampire's eyes are larger than those of many South American bats, they are of little use in dark caves so they use a kind of radar or echolocation to orientate themselves with their surroundings. They are also able to recognize other members of the colony individually and communicate with one another using a series of different sounds in the high frequency range beyond human hearing. As well as sound communication, sniffing and grooming each other helps to form bonds between individuals. Courtship can be unceremonious, with the male often treating the female quite aggressively during mating. And afterwards, males play no further part in family life. A single young vampire is born after a gestation period of about two hundred days, nearly seven months. At birth it is only sparsely furred and blind; it uses hook-like milk teeth to cling tightly to the mother's nipple since, if it fell, it would certainly perish on the floor of the cave. When foraging, the mother usually leaves her infant behind in the cave where it is cared for by older youngsters and other females in a sort of nursery. There it is kept warm and safe and may even suckle from other nursing females if its own mother is away for a long time. The young vampire continues to suckle until it is nine months old, though during that time its mother will introduce it to a blood diet by first feeding it mouth to mouth, then by having it accompany her on sorties.