Physical Description
The common vampire bat is short-haired, with silver-gray fur on its undersides, sharply demarcated from the darker fur on its back. It has small, somewhat rounded ears, a deeply-grooved lower lip, and a flat, leaf-shaped nose. A well-developed, clawed thumb on each wing is used to climb onto prey and to assist the animal in take-off. The bat averages about 9 cm (3.5 in) long with a wingspan of 18 cm (7 in). It commonly weighs about 57 grams (2 oz), but its weight can double after a single feeding. The braincase is relatively large, but the snout is reduced to accommodate large incisors and canines. It has the fewest teeth among bats. The upper incisors lack enamel, which keeps them razor-sharp. Common vampire bats exhibit sexual dimorphism in which females are bigger than males.
While most other bats have almost lost the ability to maneuver on land, vampire bats are an exception. They can run using a unique, bounding gait in which the forelimbs are used instead of the hindlimbs to propel forward, as the wings are much more powerful than the legs. This ability likely evolved independently within the bat lineage. Three pads under the thumb function like a sole. It is also capable of leaping in various directions, magnitudes and temporal sequences. When making a jump, the bat pushes up with its pectoral limbs. The hindlimbs keep the body over the pectoral limbs which are stabilized by the thumbs.
Common vampire bats have good eyesight compared to other bats. They are able to distinguish different optical patterns and may use vison for long-range orientation. These bats also have well-developed senses of smell and hearing: the cochlea is highly sensitive to low-frequency acoustics, and the nasal passages are relatively large. They emit echolocation signals orally, and thus fly with their mouths open for navigation. They can identify a metal strip 1 centimetre (0.39 in) wide at a distance of 50 centimetres (20 in), which is moderate compared to other bats.
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