Because of differences between the three species, they have each been placed within a different genus, each consisting of one species. In the older literature, these three genera were placed within a family of their own, Desmodontidae, but taxonomists have now grouped them as a subfamily, the Desmodontinae, in the American leaf-nosed bat family, Phyllostomidae.
The fact that the three known species of vampire bat all seem more similar to one another than to any other species suggests that sanguivorous habits (feeding on blood) evolved only once, and that the three species may share a common ancestor.
Unlike fruit-eating bats, the vampire bat has a short, conical muzzle. It also lacks a nose leaf, instead having naked pads with U-shaped grooves at the tip. The common vampire bat also has specialized thermoreceptors on its nose, which aids the animal in locating areas where the blood flows close to the skin of its prey. A nucleus has been found in the brain of vampire bats that has a similar position and similar histology to the infrared receptor of infrared-sensing snakes.
Vampire bats generally have small ears and a short tail membrane. Their front teeth are specialized for cutting and their back teeth are much smaller than in other bats. Their digestive system is adapted to their liquid diet, and their saliva contains a substance, draculin, which prevents the prey's blood from clotting. The vampire bats do not suck blood, but rather lap the blood at the site of the haemorrhage (where the prey is bleeding).
The inferior colliculus, part of the bat's brain that processes sound, is well adapted to detecting the regular breathing sounds of sleeping animals that serve as their main food source.
Social behavior Edit
Vampire bats are believed to be the only species of bats in the world to "adopt" another young bat if something happens to the bat's mother. Vampire bats also share a strong family bond with members of the colony, which is believed to be why they are the only bats to take up this adoption characteristic. Another unique adaptation of vampire bats is the sharing of food. A vampire bat can only survive about two days without a meal of blood, yet they cannot be guaranteed of finding food every night. This poses a problem, so when a bat fails to find food it will often "beg" to another bat for food. The "host" bat may regurgitate a small amount of blood to sustain the other member of the colony. This has been noted by many naturalists as an example of reciprocal altruism in nature.
Vampire bats hunt only when it is fully dark. Like fruit-eating bats, and unlike insectivorous and fish-eating bats, they emit only low-energy sound pulses. The common vampire bat feeds mostly on the blood of mammals (including humans), whereas both the hairy-legged vampire bat and white-winged vampire bat feed on the blood of birds. Once the common vampire bat locates a host, such as a sleeping mammal, it lands and approaches it on the ground.
Vampire bats are very agile and a recent study found that common vampire bats can, in addition to walk, run at speeds of up to 7.9 km per hour (4.9 miles per hour). They locate a suitable place to bite using their infrared sensors. They then create a small incision with their teeth and lap up blood from the wound.
"The most common species, the South American vampire (Desmodus) is not fastidious and will attack any warm-blooded animal. The white-winged vampire (Diaemus) appears to have a special preference for birds and goats. In the laboratory it has been impossible to feed Diaemus on cattle blood." If there is fur on the skin of the host, the common vampire bat uses its canine and cheek teeth like a barber's blades to shave away the hairs. The bat's razor-sharp upper incisor teeth then make a 7mm long and 8mm deep cut. The upper incisors lack enamel, which keeps them permanently razor sharp.
The bat’s saliva, which is injected into the victim, has a key function in feeding from the wound. The saliva contains several compounds that prolong bleeding, such as anticoagulants that inhibit blood clotting, and compounds that prevent the constriction of blood vessels near the wound.
A typical female vampire bat weighs 40 grams and can consume over 20 grams (1 fluid ounce) of blood in a 20-minute feed. This feeding behaviour is facilitated by its anatomy and physiology for rapid processing and digestion of the blood to enable the animal to take flight soon after the feeding.
The stomach lining rapidly absorbs the blood plasma, which is quickly transported to the kidneys from where it passes to the bladder for excretion. A common vampire bat begins to expel urine within two minutes of feeding.
While shedding much of the blood's liquid makes taking off from the ground easier, the bat still has added almost 20-30% of its body weight in blood. To take off from the ground, the bat generates extra lift by crouching and flinging itself into the air. Typically within two hours of setting out, the common vampire bat returns to its roost and settles down to spend the rest of the night digesting its meal. Excess urea from protein is thereby excreted via the urinary system of the vampire bat aided by hormones to make concentrated urine that consists of concentrated urea in small amounts of water.