Feeding Behavior

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photo taken from www.batcrew.com

The common vampire bat possesses a unique feeding style. The common vampire bat feeds solely on blood, usually the blood of mammals (Delpietro & Russo 2002; Park 1991; Lord 1993, Nowak 1991). As most bats it is a nocturnal hunter (Nowak 1991; Lord 1993). Common vampires emerge from their cave in an ordered fashion with the bachelor males leaving first harem, then the females, and lastly the harem male (Lord 1993, Park 1991). They fly to nearby pastures in search of their favorite prey-cattle, livestock, and horses (Lord 1993). The common vampire bat uses its sense of smell and hearing to find prey (Wilkinson 2001). The distance flown when foraging by females and males does not differ significantly (Wilkinson 1985a). They forage in an area five to eight kilometers from their roost (Nowak 1991). Once a victim has been targeted the bat must either land on it or walk and jump on it (Lord 1993; Nowak 1991). Common vampire bats have padded feet and wrists so that the animal does not feel the bat land (Altringham 1998). The bat then uses heat sensors in its nose to find a blood vessel near the surface (Wilkinson 1990). The most common bite sites are on the rump, flanks, and necks of animals (Lord 1993). Next, it uses its sharp teeth to pull a flap of skin off of the animal (Nowak 1991). The tongue of the vampire bat has capillary like grooves underneath and on the sides of it so that the blood can be taken up quickly (Nowak 1991). To keep the blood flowing the bat uses an anticoagulant to prevent the blood from clotting (Nowak 1991). The bat will feed for about thirty minutes, which leaves the bat swollen with blood (Lord 1993).

Common vampire bats eat their weight in blood each night, and females eat twice as much (Lord 1993). On average they eat about twenty milliliters of blood per night (Nowak 1991). The bat can barely move, so it must hide and wait until it processes the blood enough so that it can fly (Altringham 1998). Common vampires have highly efficient kidneys that beginning extracting water from the blood as soon as the bat starts eating (Lord 1993). This allows the bat to eat more blood without becoming full on water (Altringham 1998). The kidneys work to filter the water out so that the bat can fly back to the roost (Lord 1993). On a given night eight percent of the bats in a colony will unsuccessful in acquiring food (Wilkinson 1990).

Common vampire bats are protective of their victim. A vampire bat will fend off any other bats that try to land on and bite its victim while it is still feeding (Wilkinson 1985a; Wilkinson 2001). Two bats rarely use a bite site simultaneously (Lord 1993). In most cases where two bats feed from the same bite simultaneously, the two bats are mother and her offspring (Wilkinson 1985a, Wilkinson 2001). Also, vampire bats appear to prefer certain animals as victims (Lord 1993). For instance in a group of horses they will bite one specific horse once and then keep returning on consecutive nights and bite that horse again. Even when that horse is moved away from the group the bats still find it and bite it. It is thought that the urine excreted when the bat is feeding gets on the horse and marks it, so that when the same bat returns it can find the horse using the scent of the urine. It appears to be advantageous for the bats to bite the same horse, since they know from the previous night that they can successfully secure a meal from that specific horse (Lord 1993).

Common Vampire Bat Homepage--General Overview--Mating System--

Feeding Behavior--Cooperative Behavior--References