How do vampire bats survive?

Much like its fictional counterpart of books and movies, the vampire bat sleeps during the day - usually in dark caves - ventures out at night to feed. the vampire bats can be found in the tropical forests of South American through to Mexico.  

most of the vampire bat’s victims are large herbivores such as horses and cows, though human attacks are not unheard of. Most of the time, victims will rarely notice as the bats only consume about a tablespoon of blood per sitting; this said, they are often accused of spreading rabies.

Contrary to popular think, they don't actually ‘suck’ the blood either, but rather nip the skin with their sharp teeth and then lap at the blood that flows out.

Like all bats they use echolocation to get around, but they have also evolved some unique ways to hunt. For one thing they have special thermoreceptors on their noses, which - via infrared radiation — enable them to pinpoint where blood flows closest to the prey's skin, while an anticoagulant in their saliva stops blood clotting before they've had their fill. Vampires are also unusual within the bat family for their ability to walk, climb and even hop along the ground — ideal for stealthily approaching slumbering victims.