B
ats are the only true flying mammals, with about 925 different species identified. Of all these species, only the common vampire bat is able to
maneuver on the ground as well as in the air. According to Schutt (1998), vampire bats can move side to side and backward, similar to a
spider. Instead of taking off in flight from the ground, these bats actually launch themselves into the air with powerful pectoral muscles.
The force comes from the bat extending its hind knees, leaning forward and using its forelimbs. The bat also invokes its triceps muscle and very
long thumb. While the jump only takes about 30 milliseconds, the bat catapults itself about 4 feet into the air. Altenbach (1979) comments,
"although a few other species of bats move readily on the ground and some take off from the ground, no other species possess the extreme terrestrial
agility and jumping ability of Desmodus". Once in the air, the transition into flight is basically one fluid motion. Since the vampire bat
feeds at ground level, their agility and fast take-off is an amazing advantage.
F
eeding on the blood of animals like cows, pigs, and horses, the vampire bat requires about two tablespoons of blood each day. Locating their prey
is a combination of smell, sound, echolocation, and possibly heat (Altringham 1996). While they do not actually suck blood from their host, they
make a small incision and lap up the blood. Since they do not chew their food, they have fewer teeth of any other bat. They generally
approach their prey from the ground. "They have heat sensors on their noseleaf for locating capillary-rich areas of the skin; modified canines for
fur clipping; long, sharp incisors for painlessly opening a wound; anticoagulants to
prevent clotting; and a grooved tongue to help move blood rapidly to the mouth" (Altringham 1996). While the bat may consume up to 60% of its body
weight in blood and it only needs the red blood cells, it will begin excreting plasma before its meal is over. With a specialized stomach and
kidneys, the vampire rapidly removes the plasma as it may take up to twenty minutes to the bat to finish its meal (Altringham 1996). Due to length
of time and the invasive nature of its feeding, it is clear the vampire bat needs its deftness and agility to be successful. "Observations of
Desmodus scrambling over the backs and necks of animals prior to feeding (or to avoid movements of the host animal to brush them off), and running or
hopping about on the ground while feeding, illustrate the adaptive value of this effective terrestrial locomotion" (Altenbach 1996).
T
he unique social behavior of the vampire is most characteristic in their reciprocal altruism, in which animals return favors to their mutual
benefit. If vampire bats do not get their share of blood on a regular basis, they rapidly deteriorate. A bat may be close to starvation
within 2-3 days (Altringham 1996). Within social groups which largely refers to females as the males roost separately to defend territories, bats
that successfully feed will regurgitate back at the roosts to a hungry bat. Studies on the blood sharing behaviors indicate bats will regurgitate
to related and unrelated bats within the group. It is shown that they set up a buddy system, with pairs of bats forming tight blood-sharing
relationships (Altringham 1996). Refer to Figure 3 to see the weight-loss curve after feeding since donating more than 5% of its body weight will
push it too close to starvation (Altringham 1996).
Figure 3. Predictive curve of post feeding weightlosses in vampire bats (Desmondus rotundus). A donation of 5% of pre-feeding weight when at weight D
should cause a donor to lose C hours but provide the recipient at weight H with B hours. B >C for all E > F. See text for details. Redrawn from:
Wilkinson, G. S. 1984. Reciprocal food sharing in the vampire bat. Nature 308: 183.
V
ampire bats are considered agricultural pests in many parts of Mexico and Latin America where rainforests have been cut down to make way for grazing
cattle. Here, control programs are initiated to cut down on health risks to the cows. According to Anastasia Toufexis (1995)," due to the
fear associated with the vampire bat, people routinely dynamite and burn caves or roosts. Unfortunately, people also destroy very helpful, fruit
eating bats that occupy the same areas. However, the vampire bat is not endangered at this point.
C
urrently, bats are in a single order, Chiroptera (hand-winged) and are thought to have appeared 65-100 myr, in the late Palaeocene or early Cretaceous
(Altringham 1996). They are divided into two subgroups, the megabats and the microbats. Megabats refer to the large, fruit-eating bats
confined to Africa, tropical Asia, and Indo-Australia (Altringham 1996). For our purposes, we will focus on the microbats that are found on every
continent and house our common vampire bat. The oldest fossil bat dates back 50 myr in the early Eocene period (Altringham 1996). There is
poor representation of bats in the fossil record; however, some discoveries in Australia of extensive fossil bat fauna dates back 55 million years ago
(Altringham 1996). Zimmer (1998) explains, "bats are not good candidates for paleontological study. When they die, they usually
disappear…often eaten by scavengers; if not, they decompose on the ground."
M
icrobats show no close affinities to any other mammalian order, so this lack of a link suggests a very early origin. "There are a number of cases
where possibly closely related microbat species live on once adjacent, but now distant, fragments of Gondwanaland, the supercontinent which broke up
into fragments which now make up the land masses of the southern hemisphere" (Altringham 1996). When bats are thought to have been evolving, the
earth experienced dramatic diversification of flowering plants that became dominant over primitive plants of the Crenomanian period, 100-95 myr
(Altringham 1996). Insects were also supported by these flowering plants and insectivorous and frugivorous mammals must have had to compete.
The first bird dates back to the early Cretaceous, 135 myr, so they were quite abundant when bats appeared. Consequently, birds were probably
major competitors and/or predators for early bat species, which may have led to the nocturnal evolution of these small, nocturnal, tree-dwelling mammals
(Altringham 1996).
F
light in bats is one of the most fascinating evolutionary elements and currently has two theories on the table, the arboreal and the cursorial
(Altringham 1996). The arboreal suggests that tree or cliff dwelling ancestors evolved flight through a series of gliding stages. The
cursorial theory, which is more recent, requires the animal take a running leap with wings outstretched sending it into the air from a glide to flight
(Altringham 1996). With a basically absent fossil record in regard to flight, there is room for theory but little evidence.
T
o be successful night fliers, bats needed a more sophisticated system. Echolocation is orientation by analysis of echoes from sound pulses.
Due to the level of sophistication, it is presumed echolocation evolved alongside flight (Altringham 1996). Ancestors of microbats probably
emitted ultrasonic sounds in a simple form of echolocation, which became more sophisticated as bats became more adept fliers (Altringham 1996).
T
here are some recent discoveries in bat evolution that contradict common bat ancestry. The most widely accepted theory linked megabats and
microbats in the same evolutionary line. Now, there is a body of evidence suggesting convergent evolution, where evolutionary change causes
unrelated species with different histories to acquire striking similarities. The controversy has megabats, primates and dermopterans closely
related while microbats are independent (Altringham 1996). Some compelling evidence is the absence of echolocation in megabats and their limited
distribution to the Old World tropics. Altringham (1996) expands, "this evidence is very diverse, from factors as simple as a consideration of
body size ranges, to the analysis of the amino-acid sequence of hemoglobin, obtained using modern molecular biology techniques."
D
esmondus Rotundus evolved as singivores, a strange niche that is unique to bats in the New World. Indeed, all three members of the Desmodontinae
family feed on blood exclusively. Vampires may have evolved from feeding on the insects and larvae on the wounds of large mammals (Altringham
1996).
T
he common vampire, Desmodus rotundus, is widespread in the tropical and sub-tropical areas of the Americas. It occupies rainforests as well as
deserts, making its home in hollows, caves, trees, and even buildings. Usually, they live in colonies of about one-hundred bats but can reach up
to two-thousand. Preferring the blood of large mammals, the introduction of domesticated horses, cattle, and pigs has meant an increase in its
numbers over the last three-hundred years (Altringham 1996). Vampire bats move into subtropical Chile and Argentina, but they are not excluded
from temperate climates. Indeed, where there is prey, there could be a population of vampires. It is suggested, then, that the limits to its
distribution is due to the inability to transport quantities of food sufficient to maintain a high body temperature in cool to cold places (Kunz
1982). Please refer to Figure 2 for Desmondus Rotundus distribution.
Map of Distribution:
C
entral and South America are alive with folklore about the vampire bat. Legend has it that bats are filthy, feeding on human blood or that they
have supernatural powers allowing them to change shapes from man to bat. While these legends may sound strange, there is recorded evidence of
human hosts. Glover Allen (1939) talks about bats feeding on humans, "while travelling down the Amazon valley, he (Dr. William Farabee) awoke one
morning to find that a vampire during the night had gouged a small piece of skin from the tip of his nose and had evidently feasted while he slept, for
the wound was still bleeding slightly" (98). Not all tales are negative; bloodletting has traditionally held healing qualities. For example,
the Mexican monk who came down with a violent fever and was given a death sentence by morning. But, the next day, the monk was on his way to
recovery. "It seems that his feet had been left uncovered and that during the night, a vampire bat had entered the room, which, having bitten his
toe and lapped his blood, had so reduced the fever that the sick man recovered" (Allen 1939).
W
hile Western literature has embraced the vampire bat making it almost cliché, they did not appear in early vampire myth. The European folklore of
vampires did not incorporate the bat probably because they did not occur in that region (McKaig 1999). Some Gypsy folklore involved the vampire
bat but in a rather benign role; sometimes the bat’s bones would be carried in a small bag for luck (McKaig 1999). Regardless of the history,
vampire bats appear in our modern context as creepy blood-sucking creatures. They are represented in Halloween festivities often with blood
dripping from their fangs. The most recent representation of our flying mammal was the motion picture, Bats, where a colony of bats wreaks havoc
on a small Texan town. The trailers showed a swarm of screaming bats busting through car windows attacking the unassuming kids seated inside.
Adams, Rick A. and Scott C. Pederson. Jan 1994. "Wings on Their Fingers" Natural
History vol. 103, p 48-55.
Allen, Glover Morrill. 1939. Bats Dover Publications; Harvard University, New York.
Altenbach, J. Scott. 1979. Locomotor Morphology of the Vampire Bat, Desmondus
Rotundus American Society of Mammalogists; University of New Mexico, New Mexico.
Altringham, John D. 1996. Bats, Biology and Behavior Oxford University Press;
University of Leeds, New York.
Kunz, Thomas H. 1982. Ecology of Bats Plenum Press; Boston University, New York.
McKaig, Angie. 1999. "Vampire Bats"
www.pathwaytodarkness.com/facts/vampire_bats.htm
accessed 11/27/99.
Scutt, William. "Vaulting Vampires" March 1998. Discover v. 19, no. 3. P 14.
Toufexis, Anastasia. Aug 1995. "Bat’s New Image" Time vol. 146, p 58-59.
Zimmer, C. Nov 1998. "Into the Night [Bat Evolution]" Discover v. 19; no. 11, p 110-
115.
* Photograph URL for Figure 1 and 4,
http://www.geocities.com/Rainforest/Vines/3697/vbat.html
(accessed 11/20/99).
** Map URL for Figure 2,
www.thewildones.org/Animals/vampire.html
(accessed 11/20/99).
Vampire Wine
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