When Vampires get hungry…

Prey: domestic animals (cows, donkeys, horses). Even when wild prey is available, vampires will not attack it. Humans are last on the list.

Prey preferences: When given a choice between cows and horses, vampires seem to prefer horses (Wilkinson 1990). Prey preference also depends on the region, with some populations preferring domestic fowls and others cattle or burros (Dalquest 1955). This could be the difference between species, however; the common vampire (Desmodus rotundus) prefers mammalian prey, while the white-winged vampire (Diaemus youngi) prefers avian prey (Schutt et al. 1999).

Of different breeds of cattle, Swiss breeds are preferred to the Brahma breed. This could be explained by location within the herd; Swiss cattle tend to bed down for the night on the perimeter of the herd, where they are more accessible to foraging bats. (Turner 1975)

Females seem to be preferred, specifically those in estrous, to males, perhaps because they too tend to be on the perimeter (Turner 1975). D. youngi also prefers females in its avian prey than males, so hormones might be at play as well (Schutt et al. 1999).

Calves seem to be preferred, perhaps due to thinner skin (easier to bite into), or because they are less active at night, thus making easier, sessile targets. (Turner 1975)

During the rainy season, prey selectivity decreases, with several possible reasons. The herd spreads out more during this season, allowing the bats more access and thus more choices. Although they breed year round, Vampire Bats tend to have more births in the rainy season, so females have a greater need for blood. They are reduced to getting it wherever they can, no matter the breed or sex of prey. They also begin teaching their young how, where, and on what to feed during the rainy season, leading to less selectivity. These reasons also explain why bites during the rainy season are less often in the usual neck and shoulder area and are more spread out among the herd. (Turner 1975)

Foraging time: Vampires generally forage for 2 hours between 1900 and 0100 hours, with maximum foraging activity at 2100 (Wimsatt 1969). They prefer the earlier dark hours of the evening. Bats are lunarphobic and thus shift their foraging time according to moon cycles. They avoid all light as much as possible, roosting in the darkest corners of their caves or trees (Dalquest 1955).

Flight to prey: Vampires usually fly out in groups of 2-6 (contradicting Turner, who stated they hunted singly), circling around the prey animal for several minutes before landing either on the prey (if standing) or the ground next to it (if lying down) (Greenhall et al. 1971).

Bite location: Once landed, vampires either walk along the prey until they reach the neck or back, or walk along the ground until they find a sensitive area (dense in capillaries), such as armpit or udder (Greenhall et al. 1971).

Feeding: If on the animal, vampires hang head down, holding on with two points of contact (both feet or a foot and arm). From the ground, vampires stand, feeding upwards, and tend to move around more than those on top of prey. (Greenhall et al. 1971). The canines are used to shave the fur around the wound site while the incisors remove a small chunk of flesh (Schutt et al. 1999).

Feeding time: Vampires do not suck blood, rather they lap it up. An anticoagulant in their saliva prevents clotting. Feeding varies between 9 to 40 minutes, averaging around 23 (Greenhall et al. 1971). D. rotundus' prepatory period can last up to 20 minutes, a suggested reason for sequential feeding from a single wound (Wilkinson 1988), while D. youngi's prepatory feeding lasts only from 20 seconds to 2 minutes and feeding time is only 20 minutes (Schutt et al. 1999) . They have not thus far exhibited sequential feeding, perhaps because bite preparation is faster.

Amount: Vampires, with their highly extensible stomachs, have been known to consume up to 132% of their bodyweight (Wimsatt 1969), though a usual meal is 15-16 mL (Turner 1975). Bats must consume between 20-30 mL of blood every six hours to stay alive (Wilkinson 1990).

Social Interactions: Up to 4 bats have been observed feeding from the same animal at different wound sites. Generally they feed one at a time at wounds, though mothers will sometimes feed simultaneously with young, primarily female young (Wilkinson 1985a).

When feeding one at a time, the new vampire approaches the feeding vampire until they are next to each other, and after some pushing around the feeder usually flies off as the newcomer starts eating (Greenhall et al. 1971). Other interactions can be more aggressive, including jumping, fighting, and screaming. In Greenhall's study, one particular vampire was aggressively territorial on a particular cow, chasing away all comers even when it had finished its meal. Turner also observed this behavior. Perhaps the difference between these two cases is the degree of association between the feeding bat and the newcomer: if the newcomer has a high degree of association (a roostmate, for example), there will be much less aggression than if it is a stranger.

Turner suggested that aggression on prey was a holdover from prehistoric times, when prey was much less abundant. Arboreal feeding might have developed in that era of scarcer prey to reduce competition where ranges between common and white-winged vampires overlapped, though Schutt and Altenbach suggest that arboreal predation is ancestral (Schutt et al. 1999). This makes sense, as vampires in general would have had to utilize avian prey in place of the large herds prevalent in modern times.

Foraging Range: Turner found no difference between male and female foraging range and recapture rates and distances, and Wilkinson found similar average foraging distances of the two sexes. Counter to Turner's hypothesis that vampires switch roosts to maintain maximum proximity to prey, Wilkinson found distances traveled were roughly twice the mean roundtrip distance from roost to prey (Turner 1975, Wilkinson 1985a). He noted that males from non-favored trees (those that rarely or never had females) flew up to 10 km/night (Wilkinson 1988).

Male and female ranges rarely overlap as opposed to female-young and female-female ranges (Wilkinson 1985a). Turner observed that males appear to feed later in the evening than females, and that not until 0300-0500 did 50% of males had full stomachs. He postulated that males might be off

Please note this is an undergraduate website created for Animal Behavior 323 at Davidson, College, NC, by Julie Perry. Questions, comments, suggestions, corrections: please email Juperry@davidson.edu

© Copyright 2002 Department of Biology, Davidson College, Davidson, NC 28035 - - - - - - - - - - - - - - - - - - - - Last updated: 19 April 2002