Vampire Bats and Reciprocity - Musings on the Natural World.

When one utter aloud the word “vampire”, one conjures mental pictures of Bram Stoker’s monster. And his tiny fluttering mammalian counterparts.

The common perception of a vampire bat is that of leathery winged ghouls. Whom, in the dead of night, fly off into a pitch black night. In search of unsuspecting beasts and folk. Whereupon they haphazardly sick their needle-sharp incisors deep into slumbering, virginal flesh. Feasting upon the lifeblood of their hapless victims. Suctioning up blood like living syringes. Exchanging another’s mana for their own.

Uncaring. Unkind. Unloveable.

Or, so there story goes.

But the truth is more nuanced.

Studies of vampire bat society has actually found the contrary to this popular depiction. Vampire bats are surprisingly social creatures, with excellent memories.

Vampire bats lead surprisingly harsh lives. The common vampire bat can not survive more than a few days without a blood meal. So, Vampire Bats, on the odd occasion, are reliant on regurgitated donations from other bats from their colony to survive.

But Vampire Bats aren’t saints.

Studies have found that they only share with bats that A) have shared with them previously or B) Have never had the opportunity to share with them in the past (i.e a first encounter, ala Hawk vs Dove). If a vampire bat has interacted with that bat before, and that bat had, on that prior occasion, refused to share with them, then the vampire bat would now ignore that bat’s cries for regurgitated blood.

Letting another vampire bat die is a bit harsh, but fair is fair.


Much of the work done in human psychology on altruism and reciprocity also finds we are likely to act favourably to those who, in the past, have responded favourably to us. Studies have found we are more likely to share with those who have shared with us. Other studies have found that the more we encounter an individual, the more inclined we are to want to behave in a kind way towards them. The less kind others are to us and the less we interact with them, typically leads to less reciprocal behaviours on our behalf.

That said, the work on reciprocity in humans is complicated by the laws of diminishing returns and sunk cost phenomenon. Namely, we are more likely to invest our time and energy into things we have invested in the past. Benjamin Franklin was an expert in reverse reciprocity. He would borrow books from his enemies. If they loaned him a book, it would be impossible for them to reconcile that they disliked him and that they were doing him a favour at the same time. Asking a favour ended up becoming the way that they would (eventually) become friends. Sharing is caring….