Vampire bats rarely attack humans because free-ranging cattle provide a more readily accessible food source. Vampire bats are also extremely light-sensitive; attacks on humans only occur in dimly lit areas, such as campsites or indigenous villages.
Only one of the three extant species of vampire bat is a generalist in feeding: the common vampire bat. The other two species, white-winged and hairy-legged, are almost exclusively avian predators. As such, the common vampire bat is the only species likely to find humans suitable prey; however, it is more detrimental to domestic livestock than to humans. When Europeans brought cattle to the New World, they changed the feeding habits of the species. Cattle often graze outdoors and are left in the open at night, and as a result have become an important food source for the common vampire bat. Unfortunately, this spreads diseases, like rabies, among the herd. When cattle and other livestock are easily accessible as prey, vampire bats have little need to enter human dwellings to seek a meal.
Vampire bats are also extremely light-sensitive. Any areas inhabited by humans are often too brightly lit to be enticing. They have been know, however, to feed on humans camping in tents; they are also problematic in indigenous villages.
In August 2010, Peru experienced a surge in vampire bat attacks on humans, mostly children. Deforestation is one probable cause of this change in behavior. As the vampire bat's habitat continues to diminish, it will come into increasing contact with people. In an interesting development to this issue, several Peruvians have rabies antibodies present in their blood, even though they do not have the rabies vaccine. They do, however, all have a history of vampire bat bites.