Vampire bat

For the 1933 movie, see The Vampire Bat.

Vampire bats
Common Vampire Bat, Desmodus rotundus
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Chiroptera
Family:	Phyllostomidae
Subfamily:	Desmodontinae Bonaparte, 1845
Genera
Desmodus Diphylla Diaemus

Vampire bats are bats whose food source is blood, a dietary trait called hematophagy. There are three bat species that feed solely on blood: the Common Vampire Bat (Desmodus rotundus), the Hairy-legged Vampire Bat (Diphylla ecaudata), and the White-winged Vampire Bat (Diaemus youngi). All three species are native to the Americas, ranging from Mexico to Brazil, Chile, and Argentina.

Species

Due to 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.^{[citation needed]}

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.^{[citation needed]}

Anatomy

A vampire bat skeleton, showing the distinctive incisors and canines.

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,^[1] 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.^[2][3]

Vampire bats generally have small ears and a short tail . Their front teeth are specialized for cutting and their back teeth are much smaller than in other bats. 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.^{[citation needed]}

While other bats have almost lost the ability to maneuver on land, Vampire bats can also run by using a unique bounding gait, in which the forelimbs instead of the hindlimbs are recruited for force production as the wings are much more powerful than the legs. This ability to run seems to have evolved independently within the bat lineage.^[4]

Vampire bats use infrared radiation to locate blood hotspots on their prey, according to a study published in Nature^[5]. The infrared signals are received through the bat's three 1mm-diameter leaf pits, which are located around their noses and can change direction when needed. The only other vertebrates capable of detecting infrared radiation are boas, pythons and pit vipers, all of which have pit organs. A mass of nerve cells called trigeminal ganglia (TG) - which are associated with the trigeminal nerves responsible for causing sensations in the face - stimulate the leaf pits. The TG of vampire bats have large diameter neurons, similar to those of pit-bearing snakes, while fruit bats have a much smaller trigeminal ganglia. ^[6]

Ecology and lifecycle

Vampire bats tend to live in colonies in almost completely dark places, such as caves, old wells, hollow trees, and buildings. They range in Central to South America and live in arid to humid, tropical and sub tropical areas. Vampire bats live in colonies that can number in the thousands in roosting sites. The basic social structure of roosting bats is made of harems which are composed of females and their offspring and a few adult males, known as "resident males" and a separate group of males, known as "non-resident males".^[7] In hairy legged vampire bats, the hierarchical segregation of non-resident males is less strict than in common vampire bats.^[7] Non-resident males are accepted into the harems when the ambient temperature lowers. This behavior suggests social thermoregulation.^[7]

Resident males mate with the females in their harems, however it is common for outside males to copulate with the females.^[8] Female offspring usually remain in their natal groups unless their mothers die or move.^[8] Several matrilines can be found in a group as unrelated females regularly join groups.^[8] Male offspring tend to live in their natal groups until they are about two years old, sometimes being forcefully expelled by the resident adult males.^[8]

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.^[9] 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" 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.^[10] Vampire bats also engage in social grooming.^[11] It usually occurs between females and their offspring, but it is also significant between adult females. Social grooming is mostly associated with food sharing.^[11]

Feeding

A vampire bat feeding on a pig (taxidermy specimens)

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. It then likely uses thermoception to identify a good spot on the skin to bite.

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.^[12] They then create a small incision with their teeth and lap up blood from the wound.

As noted by Arthur M. Greenhall:

“

The most common species, the common 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 not been possible to feed Diaemus on cattle blood.[13]

”

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.^[14]

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,^[15] and compounds that prevent the constriction of blood vessels near the wound.

Digestion

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.^[16] 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.^[17] 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.^{[citation needed]}

Human health

Vampire Bat at the Louisville Zoo

Only 0.5% of bats carry rabies. However, of the few cases of rabies reported in the United States every year, most are caused by bat bites.^[18] The highest occurrence of rabies in vampire bats occurs in the large populations found in South America. However, there is less risk of infection to the human population than to livestock exposed to bat bites.^[19]

Although most bats do not have rabies, those that do may be clumsy, disoriented, and unable to fly, which makes it more likely that they will come into contact with humans.

The unique properties of the vampire bats' saliva have found some positive use in medicine. A study which appeared in the January 10, 2003 issue of Stroke: Journal of the American Heart Association, tested a genetically engineered drug called desmoteplase, which uses the anticoagulant properties of the saliva of Desmodus rotundus, and was shown to increase blood flow in stroke patients.

Role in fiction

Main article: Vampire

The vampire bat is often used in movies and books about vampires. Fictional vampires also consume blood, usually in order to survive. Comparable to the actual vampire bat, the most common feeding method is piercing a hole in the victim's neck with sharp fangs and sucking blood from the pierced area. Fictional vampires are also commonly nocturnal, and rarely come out during the day, similar to vampire bats. Other attributes of fictional vampires include, but are not restricted to, the ability to transform into a vampire bat and animal-like senses of sight and hearing. In several vampire horror films a vampire bat arrives through the victim's window then magically transforms into the fictional mythological creature.^{[citation needed]}

Footnotes

1. ^ Klaus Schäfer, Hans A. Braun and Ludwig Kürten, (2004) "Analysis of cold and warm receptor activity in vampire bats and mice", Pflügers Archiv European Journal of Physiology, 412(1-2):188-194
2. ^ Angela L. Campbell, Rajesh R. Naik, Laura Sowards and Morley O. Stone (2002). "Biological infrared imaging and sensing". Micron 33 (2): 211–225. doi:10.1016/S0968-4328(01)00010-5. PMID 11567889. http://web.neurobio.arizona.edu/gronenberg/nrsc581/thermo/biologicalinfraredsenses.pdf. 
3. ^ *Kishida R, Goris RC, Terashima S, Dubbeldam JL. (1984). "A suspected infrared-recipient nucleus in the brainstem of the vampire bat, Desmodus rotundus". Brain Res. 322 (2): 351–5. doi:10.1016/0006-8993(84)90132-X. PMID 6509324. 
4. ^ Riskin, Daniel K. and John W. Hermanson. 2005. Biomechanics: Independent evolution of running in vampire bats. Nature 434: 292-292. Abstract, video.
5. ^ http://www.nature.com/nature/journal/v476/n7358/full/476040a.html/
6. ^ http://www.cosmosmagazine.com/news/4584/vampire-bats-can-see-blood/
7. ^ ^{a b c} H.A. Delpietro, R.G. Russo. (2002) "Observations of the common vampire bat (Desmodus rotundus) and the hairy-legged vampire bat (Diphylla ecaudata) in captivity", Mammalian Biology 67(2): 65-78.
8. ^ ^{a b c d} Wilkinson, G. S. (1985). "The Social Organization of the Common Vampire Bat II:Mating System, Genetic Structure and Relatedness." Behavioral Ecology and Sociobiology 17(2): 123-134.
9. ^ [1]
10. ^ Dawkins, Richard (2006) "The Selfish Gene", Oxford University Press p. 232
11. ^ ^{a b} Wilkinson, G. 1986. "Social grooming in the common vampire bat, Desmodus rotundus". Animal Behaviour, 34 (6): 1880-1889.
12. ^ [2]
13. ^ Greenhall, Arthur M. 1961. Bats in Agriculture, p. 8. A Ministry of Agriculture Publication. Trinidad and Tobago.
14. ^ Greenhall, Arthur M. (1988) "Feeding Behavior". In: Natural History of Vampire Bats (ed. by A. M. Greenhall and U. Schmidt), 111-132. Boca Raton, FL: CRC Press.
15. ^ Christine Hawkey (1966) "Plasminogen Activator in Saliva of the Vampire Bat Desmodus rotundus", Nature, 211:434-435
16. ^ McFarland, W. N., and W. A. Wimsatt. (1965) "Urine flow and composition in the vampire bat". Amer. Zool., 5:662-667.
17. ^ Schutt, W. A. Altenbach, J. S. Chang, Y. H. Cullinane, D. M. Hermanson, J. W. Muradali, F. Bertram, J. E. A. (1997) "The dynamics of flight-initiating jumps in the common vampire bat Desmodus rotundus", Journal Of Experimental Biology 200(23):3003-3012
18. ^ Gibbons, Robert V.; Charles Rupprecht (2000). "Twelve Common Questions About Human Rabies and Its Prevention" (PDF). Infectious Diseases in Clinical Practice (Lippincott Williams & Wilkins) 9 (5): 202–207. doi:10.1097/00019048-200009050-00005. ISSN 1056-9103. http://www.cdc.gov/rabies/docs/12_questions_rabies.pdf. Retrieved 2007-12-29. "Excluding dog bites that occurred outside of the country, 22 of the 31 (71%) human cases of rabies in the United States since 1980 have been associated with bat rabies virus variants."  Note: the 71% figure in the quote would be for the 20 year period from 1980 to c.2000.
19. ^ http://www.si.edu/Encyclopedia_SI/nmnh/batfacts.htm

Further reading

• Greenhall, Arthur M. 1961. Bats in Agriculture. A Ministry of Agriculture Publication. Trinidad and Tobago.
• Greenhall, Arthur M. 1965. The Feeding Habits of Trinidad Vampire Bats.
• Greenhall, A., G. Joermann, U. Schmidt, M. Seidel. 1983. Mammalian Species: Desmodus rotundus. American Society of Mammalogists, 202: 1-6.
• A.M. Greenhall and U. Schmidt, editors. 1988. Natural History of Vampire Bats, CRC Press, Boca Raton, Florida. ISBN 0849367506; ISBN 978-0849367502
• Campbell A, Naik RR, Sowards L, Stone MO. (2002). "Biological infrared imaging and sensing". Micron 33 (2): 211–225. doi:10.1016/S0968-4328(01)00010-5. PMID 11567889. http://web.neurobio.arizona.edu/gronenberg/nrsc581/thermo/biologicalinfraredsenses.pdf. 
• Pawan, J.L. (1936b). "Rabies in the Vampire Bat of Trinidad with Special Reference to the Clinical Course and the Latency of Infection." Annals of Tropical Medicine and Parisitology. Vol. 30, No. 4. December, 1936.

External links

• Schutt, W.A., Jr. "Dark Banquet" a website devoted to the biology of blood feeding creatures.
• Bat Conservation International - A website devoted to the education, conservation and study of bats.