Vampire bats are active only during the darkest 
periods of the night.  It is the time when they are most likely 
to avoid being caught by such nocturnal preditors as owls.  
Also, the domestic animals on which the bats feed are often 
sleeping, and so are easier to approach undetected.
   During the day, vampire bats roost in colonies, hanging 
upside down in caves and hollow trees.  They will sometimes 
move from one daytime roost to another which is closer to their 
prey.  This kind of activity indicates that vampire bats learn 
from experience where their prey can be found.
   Vampire bats also use rivers as navigational tools as they 
move from one part of their range to another.  The rivers are 
easier to follow than wooded routes, and cattle often graze in
pastures near water.

   The vampire bat feeds on the blood of animals.  Cows,
pigs, and horses are its favorite hosts.  The bat will usually 
choose to feed on the most docile or isolated animal in the 
resting herd.  Using its chisel-like incisor teeth, the bat makes 
a small cut in the animal's skin.  It usually chooses a fleshy area, 
like the shoulder or neck, where the blood vessels are closer to 
the skin's surface.
   The bat then drinks (or rather laps) the blood that flows from 
the wound.  Chemicals in the bat's saliva keep the blood flowing 
for the 2 - 3 minutes that the bat feeds.  The bat's tongue has 
two lateral grooves which alternately open and close while the 
bat is feeding. This action draws the blood up the deeply 
grooved lower lip, channeling it into the mouth.  An adult vampire 
bat will consume about five teaspoons of blood per day.
   Often two or three bats will feed from the same wound.  In most
instances, the host animal suffers no ill effects from the loss of 
blood, although if too many bats feed on the same animal, it may 
be severely weakened.

   The vampire's ability to reproduce is limited by its need 
to remain light enough to fly.  It gives birth to a single offspring 
after an unusually long gestation period of six to eight months.
   Born blind, the young bat is carried by its mother for the first 
few days of its life.  Its eyes open after a week, and it takes its 
first flight when it is three weeks old.  The young bat is sexually
mature at nine months and breeds at any time of the year.  
Mating takes place while roosting upside down in the security 
of a cave.

   The vampire bat can transmit rabies to livestock and 
man, although this is a rare occurance as less than 1% of 
vampire bats carries the disease.  To control the vampire bats, 
cattle have been injected with anticoagulants, substances that 
do not harm the cows but will cause internal bleeding in the 
feeding bats.  Anticoagulants have also been smeared on the 
bats themselves.  When they return to their roost site, other 
bats in the colony groom them and ingest the fatal drug.