Bats are a diverse and complicated character within human culture – folk tales speak of bats curdling breast milk, countless films and books have depicted bats as the disguise for hunting vampires, Shakespeare described bats being used for witches’ spells, Chinese legends uphold the bat as a symbol for happiness and good fortune, and the Babylonians believed bats were the physical manifestation of dead souls. However, aside from their cultural presence, bats are a fascinating and sophisticated species.
Vampire bats in particular have developed many unique and extremely specialized behaviors which have allowed them to be a competitive species within the animal kingdom. As pointed out by Dr. Bill Schutt, much of the research conducted on vampire bat behavior has focused on the common vampire bat (Desmodus rotundus) – one of the three species of vampire bats – under the assumption that their behavior could also be attributed to the other two species of vampires: the white winged vampire bat (Diaemus youngi) and the hairy-legged vampire bat (Diphylla ecaudata). Upon further investigation and observation however, Schutt was able to determine that the behaviors in vampire bats were varied and that their feeding behaviors proved to be the most diverse.
In the case of the common vampire, ground hunting is the preferred method for obtaining blood, “One of the reasons for the common vampire’s success is its ability to feed from the ground—and thanks to humans – they have developed a partiality to cows’ blood. This they often obtain while on the ground, from the region behind the cows’ hooves, an area with relatively thin skin and an ample blood supply flowing close to the surface” (Schutt). This behavior has led to distinct physical traits within Desmodus such as strengthened pectorals and elongated thumbs which allow them to jump away from potential kicks by their bovine prey and take flight off the ground.
The white winged vampire is a much daintier species. In contrast to its common vampire cousin, Diaemus prefers to hunt in the trees. By hanging on the branch below a roosting bird the white winged vampire licks the foot or toes of its prey (all vampire bats do this as their saliva acts as an anticoagulant). Once the site prepared, Diaemus bites down and then laps the blood until it is ready to take to the air from the branch (Schutt). This method of hunting has contributed to Diaemus developing smaller thumbs than the afore mentioned Desmodus. A behavior observed from white winged vampires in captivity reveals a layer of cunning to their otherwise polite style of hunting. Schutt explains,
The other bat, however, crept even closer, and then, amazingly, it nuzzled against the hen’s feathery breast. Instead of becoming alarmed or aggressive, the bird seemed to relax. The vampire responded by pushing itself even deeper into what I would later learn was a sensitive section of skin called the brood patch: a feather-free region, densely packed with surface blood vessels, where body heat is efficiently transferred to the hen’s eggs or to her chicks. As I watched, the hen reacted to the bat by fluffing her feathers, hunkering down—and closing her eyes. (Schutt)
The bats had learned to act the part of a chick, in order to calm the hen and gain access to the blood-rich underside of her breast.
The final species of vampire bat, the hairy-legged vampire, is not afraid to get up close to its prey. As Schull witnessed, this vampire hangs from the underside of the chicken and feeds from around the cloaca (contrast to the white wing which hangs from a branch and feeds mainly from the feet).
In each case, it can be seen that the behavior of an animal influences the ways in which they physically develop and alter. Most of the time when I think of evolution changing the physical characteristics of an organism it is in response to external forces like climate, habitat, and predation but in these instances it seems that it was the chosen behavior of the bats that altered their physical adaptations.
Schutt, Bill. “The Curious, Bloody Lives of Vampire Bats.” Natural History. Natural History Museum and Magazine, n.d. Web. 3 Dec. 2015.