Common Vampire Bat, Desmodus rotundus

The common vampire bat (Desmodus rotundus) is endemic, or native, to the Americas. It is actually a leaf nosed bat, although it is one of only three parasitic mammals. It can be found in South America, Central America, and in parts of Mexico. In southern Brazil, it is the most common type of bat. The common vampire bat has a southern range including Chile, Uruguay, and northern Argentina. Preferring humid, warm climates, this vampire bat only resides on Trinidad in the West Indies. This bat will go as far north as 170 miles past the border of the United States.

This bat will roost in forests on trees, in caves, and in human structures like old wells and mines. They are known to roost with nine other species, but they are the most dominant among them. They will choose to roost in the darkest spots, and once they are gone, other bats will take over the prized spots. The vampire bat has a conservation status of least concern because of its wide population range, its ability to accommodate too many habitats, and because its chances of population decrease on a level of concern are low.

First classified as in 1810 as Phyllostoma rotundum by Étienne Geoffroy Saint-Hilaire, the common vampire bat underwent a series of changes in classification until 1901 when Oldfield Thomas gave  it its current name of Desmodus rotundus. There are two other species with the common vampire bat in the subfamily Desmodontinae, known as the hairy-legged vampire bat and the white-winged vampire bat. These are known as the “true” vampire bats, and are separated from the “fake” vampire bats of the Megadermatidae family, and the spectral bat.  This bat differs from the other members of its subfamily in that it feeds on the blood of mammals, whereas the hairy-legged vampire bat and white-winged vampire bat feed on the blood of birds. It can also be distinguished from the other vampire bats by its longer thumb. It is the only existing member it its genus.

The common vampire bat has the typical leaf shaped nose of the leaf nosed bat kind. It is silver-ish brown in color, with a noticeably darker shade of fur on its back. Its ears are small and slightly rounded and it has a deeply grooved lower lip. The common vampire bat can have an average body length of 3.5 inches, with typical weight of 2 ounces prior to feeding when it can weigh 4 ounces. Its wingspan averages seven inches long. Although the skull is large, the face of this bat is small, in order to accommodate its large teeth. This bat has the least amount of teeth of all bats, and the teeth lack enamel, which keeps them sharp. Its long thumbs make this bat able to latch onto prey, and also aids in flight take-off. Females are usually larger than males denoting a sexual dimorphism.

The movements of the common vampire bat are different from that of other bats. It is able to move on land, using the power from its wings to run. It does not run on its hind legs, but will use its front feet to push forward. It is thought that this behavior is an evolutionary trait. The common vampire bat can also leap, using its front limbs to launch in a variety of directions. It uses its hind legs and thumbs to balance itself while jumping
These bats have better eyesight than most other bats, and this allows them to distinguish more optical patterns and makes it possible for them to see over long distances. Their sense of smell and hearing are also good, and they will use echolocation to navigate.

The typical diet of the common vampire bat consists of mammalian blood, specifically that of cattle and livestock. They have been known to feed on wild animals such as the tapir, but prefer domesticated animals. If given a choice they will feed on horses more than cows, and females in estrous are more likely to be targeted. Using echolocation at night, common vampire bats will feed at a distance between 3.1 to five miles from their roost, leaving in an orderly fashion. Bachelor males will go first, followed by females, and the harem males will leave last. Usually, the bat will land or jump onto the neck, rump, or sides of its prey, latching on with its thumbs. This bat has heat sensors in its nose that allow small surface blood vessels to be detected. After biting into the creature, the bat will tear away a small piece of skin, and lap up the blood that pools there. In order to keep the blood from clotting, there is an anticoagulant with the bat’s saliva. The bat can feed for up to thirty minutes. The blood is stored in the cardiac notch near the stomach, and must be digested before the bat can fly home. It is a common occurrence for the bat to feed off the same creature the next night, after having marked it with urine. Bats are territorial of their prey, and will fight off any other bats looking to steal their prey. The exception to this aggressive behavior is mother and baby bats.

Common vampire bats display a large amount of social relationships within their groups. Female bats within a harem have greater relationships than with the males. If there is more than one male, the chances of a relationship between them are not as high as with females. If strange male bats enter the harem, they are accepted for keeping body temperatures stable, but there is a chance for aggression to occur. Although bats are territorial over prey that has been marked, they will share food among other members of the harem by means of regurgitation. It is thought that this happens in order to keep starvation out of the harem. Vampire bats cannot survive if they do feed within three days. Females are most apt to share blood with each other, followed by males sharing with females. It is also possible for males to share blood.

Female vampire bats within a harem practice alloparenting, where other lactating females take the responsibility of feeding the young. This occurs whether the mother is alive or dead. This happens in order to ensure that no baby bat goes hungry, and to ease the burden of parenthood. Mutual grooming is also practiced in harems, providing a convenient cleaning method and the means to strengthen social bonds. Grooming is also a good way to determine whether a bat is in need of food. Mothers will groom their babies more often than other bats, and this may create a form of recognition.

Most bats do not have rabies, according to the Centers for Disease Control and Prevention, and only about six percent  of those who were captured by cats, sick, or weak contracted the disease. Even with this low number, most reported cases of rabies in the United States are from bat bites. In South America, there are larger chances of rabies occurring, and this happens typically among livestock. In 1932 Dr. Joseph Lennox Pawan, a government bacteriologist in Trinidad, found the first bat with rabies. Soon after this discovery, Pawan was able to conclude that not only vampire bats, but also other bats including fruit bats, were able to carry and transmit this disease with little to no symptoms.

If a bat is infected with rabies, common symptoms include the inability to fly, disorientation, and clumsiness. Bats infected with rabies are more likely to have contact with humans than bats who are not infected. Studies have shown that it may be possible for bat to contract rabies purely through the air, and so it is strongly cautioned that any human who has had contact with a bat inside their home should seek medical attention. Although there are dangers involved with vampire bats, unreasonable fear of bats is not necessary, and they have actually provided humans with a positive benefit. The anticoagulant from its saliva has been found to increase the blood flow of stroke victims, and is used in a medicine called desmoteplas .

Image Caption: Common Vampire Bat, Desmodus rotundus. Credit: Wikipedia (CC BY-SA 3.0)