San Francisco State University
Geography 316: Biogeography
The Biogeography of Vampire Bat (Desmondus
rotundas)
by Nikki Michel, student in Geography 316, Fall 1999
Common name: vampire bat
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Chiroptera
Family: Desmodontidae
Genus: Desmondus
Species: Desmondus rotundus
Description of Species
Vampire bats are very ordinary looking, weighting about one ounce and
with a body the size of an adult’s thumb. They are 2 3/4 inches in length and
have an 8 inch wingspan. Please refer to Figure 1 for a photograph of Desmondus
rotundus. Their colonies are quite structured with strong social bonds, grooming
each other and recognizing their fellows with voice and smell. The structure is
imperative to their survival, as there are many nights when a bat may not find a host to
feed on. At that point, the hungry bats are fed from others through a process of
regurgitation. In the wild, vampire bats live to about 9 years old, but can reach 20
years in captivity. Vampire bats mate all year round and usually have only one
offspring per year. Gestation is 6-8 months in length.
Natural History
Bats 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.
Feeding 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).
The 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.
Vampire 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.
Evolution
Currently, 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.”
Microbats 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).
Flight 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.
To 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).
There 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.”
Desmondus 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).
Distribution
The 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:
Other interesting issues
Central 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).
While 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.
Bibliography
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).
send comments to bholzman@sfsu.edu
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