photo courtesy Verna Case

 

There are 925 species of bats in the world and the common vampire bat is one of the smallest. Their body size is roughly that of an adult thumb, with an average length of 3 inches, a wingspan of 8 inches, and weighs about one ounce. It is important for them to be small, so that they can crawl around on their prey without being detected. It is said that "they look like a pig with fangs and large pointy ears" (Drew 2001). Like other bats, they have fur covering their body and have leathery wings. At the tips of the wings are claws that they use for holding onto their prey and for climbing in their roost. There is female based sexual dimorphism in vampire bats, meaning that the females are typically larger than the males. Most bat species do not exibit sexual dimorphism. Russo and Delpietro(1995) attribute the dimorphism in vampire bats to the fact that the females breast feed their young for a longer time than in other bats, so they need the extra weight in order to occomodate for the extra energy requirement.

Vampire bats live up to nine years in the wild and up to 19 years in captivity. The vampire bat’s major predators are humans, eagles, owls, and hawks (Drew 2001).

 

photo courtesy of Jeane Vogel

 

Habitat

Vampire bats find their home in tropical and subtropical areas of central and south america. They are found as far north as Mexico and as far south as Brazil. Their habitats range from desert to rainforest. As long as the temperature is warm enough, there are places to roost, and livestock to feed on; vampire bat colonies are likely to survive (Drew 2001).

Vampire bats are nocturnal so they spend their time roosting during the day. They make their roosts out of hollow trees, caves, barns, or even buildings (Holzman 1999). Most of their roosting time is spent in day roosts, where they pass the day time hours expending little energy. They also have short term night roosts where they may take a rest during a night of feeding. The night roosts are typically on tree branches about two meters off the ground (Wilkinson 1984).

The bats may utilize a single roost for several years, but they do not show fidelity to individual roosts. Eleonora Trajano (1996) conducted a study on movements of vampire bats and found that the range of the bats is only 2-3 km in radius. Within this radius there may be several roost sites, which they may alternate between. They do show fidelity to these groups of roost sites. In warmer climates any size roost may be used because temperature regulation is not an issue. However, during cold seasons, the bats are confined to larger roosts that are more isothermic because small trees may become too cold at night, whereas large caves stay at a relatively constant temperature year round. Because there is a limited number of roost sites during the colder seasons, some bats are forced to migrate to warmer climates in order to find a roost site. Also, during cold weather the herds of cattle tend to cluster making it difficult for many bats to feed undetected. So, this clustering may be another reason why the bats migrate to warmer temperatures where herd clustering does not occur. Bat migration is different than bird migrations, though, because not every bad migrates, only enough to decrease the pressure of high roost population density, and feeding pressure (Trajano 1996).

 

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