Much of the behavior exhibited by common vampire bats revolves around their feeding habits of drinking blood from birds and mammals, preferentially livestock due to their abundance (2) (7). A common vampire bat finds its prey with echolocation, smell, sound, and possibly heat; it then uses special heat sensors in its nose to find veins that are close to the skin (3). These bats do not actually suck blood from their host, but rather make a small incision and lap up the blood (8), with an anticoagulant in their saliva preventing the blood from clotting (9). Vampire bats live in large colonies in which there are groupings of 8 to 12 females that roost close together on a regular basis, and single males roosting separately, defending territories (2) (3). Within these smaller female groups individuals exhibit a rare example amongst animals of reciprocal altruism, involving a remarkable blood-sharing behaviour in which well-fed bats regurgitate blood to hungry companions (3). Individuals are not always successful in hunting, and hungry bats may starve to death within three days (4). Studies indicate that females will regurgitate to related and unrelated bats within the group, demonstrating a mutual 'buddy system', with pairs of bats forming tight blood-sharing relationships (3). Associations between females are maintained over many years (2), and partner fidelity appears to be central to the persistence of this amazing reciprocal-exchange system (4). Common vampire bats mate year round, with birth peaks during April and May and in October and November (7). Most females have one pregnancy per year, although more than one is possible (2), and single offspring are usual (7). The gestation period is about seven months (2), and pups are born with their eyes open (7). The mother nurses the pup for the first two months (7), introducing regurgitated blood meals to them during their second month, and at four months the pup leaves the nest to accompany its mother on hunts (2). A common vampire bat lives up to 12 years in the wild (2).