Do kind-hearted vampires exist?
Many of us have seen this animal appearing in movies and fictional stories, transforming into blood thirsty vampires and mercilessly preying on helpless humans. This misleading portrayal of the common vampire bat (Desmodus rotundus) as a vicious and cold-hearted creature is not entirely true and here is one reason why:
Vampire bats are one of the few species that display reciprocal altruism.
How and why do the vampire bats display such an act of kindness by sharing its food?
Here’s the story:
On a bad night, a bat goes back to its roost without a successful hunt. If it does not feed on blood for another 48 hours, it will most likely starve to death. When this happens, another bat will regurgitate blood to the starving bat, increasing its chances of surviving, at least for another night (Wilkinson, 1990). A relationship is formed between the bats where the regurgitating bat expects the starving bat to reciprocate the next time it fails to find food (BBC). Hence, a buddy system is formed. In order for this to work, it is crucial that the bats in the system are able to recognise each other and prevent any cheat. This is achieved through “social grooming” and “individually distinct vocalizations” (Wilkinson, 1990: 81).
Gerald S. Wilkinson observed that blood sharing was not random (Wilkinson, 1990). Instead, it is based on the (kin) relatedness of the bats and also on associations between unrelated bats that were established over time. In addition, another important criterion of reciprocity is that the cost of sharing blood by the donor must be small compared to the benefit that the recipient gains. In other words, if the sharing of food puts the donor bat’s life at risk, it will not regurgitate blood eventually (Wilkinson, 1990).
As the proverb goes: “Every man for himself”. Or rather, every bat for itself.
“Moral maze,” by BBC. URL: http://www.bbc.co.uk/science/humanbody/mind/articles/personalityandindividuality/morals.shtml (accessed on 31 Mar 2013).
GS Wilkinson, 1990. Food sharing in vampire bats. Scientific American, 262(2): 76-82.
“Bat, Vampire -2- (Desmodus rotundus),” by Robertsphotos1. Flickr, 10 Nov 2008. URL: http://www.flickr.com/photos/32357208@N08/3019043473/ (accessed on 31 Mar 2013).
“Vampire bat food sharing (explained by David Attenborough),” by Gerald Carter. YouTube, 14 Jul 2011. URL: http://www.youtube.com/watch?v=rZTAW0vPE1o (accessed on 31 Mar 2013).
“Altruism,” by SciShow YouTube Channel. YouTube, 3 Jul 2012. URL: http://www.youtube.com/watch?v=jKtOXvA14X4 (accessed on 31 Mar 2013).