What a Vampire Bat Can Teach Us About the Economics of Friendship
A Smithsonian scientist says important lessons about making friends and sharing can be learned from these blood-sucking creatures
The blood-sucking vampire bat may have a lesson to teach us on what sharing is all about. If you don't believe this, Gerald Carter can prove it with his new research paper, "Social Bet-Hedging in Vampire Bats." By observing how vampire bats make friends and share food, Carter has figured out some evolutionary facts of friendship that could potentially apply beyond the world of bats and blood.
“This is what we do every night,” he says, slipping through a screen door into a dark, wire enclosure with black plastic tacked up around the walls. Vampire bats dangle from the corners of the ceiling like fuzzy brown fruit. There is a strange, thick animal scent in the humid Panamanian air. At the Smithsonian Tropical Research Institute (STRI) facility in Gamboa, Panama, Carter, a behavioral ecologist, has been able to study vampire bats both in the wild and in captivity for years.
Wearing a special glove, he picks out one particular flapping little vampire bat and examines it. “We come in here and the bats have these little bands and their names are just their bands,” Carter says. “This one is Shiny, for the shiny band.”
Shiny looks annoyed. Also cute. Carter stretches Shiny's wing out to demonstrate the little grasping claws used to grip and climb. Shiny has a fuzzy belly and very soft, velvet-like wings. The captive bats have allowed Carter to ask a pretty big question about the bats and about living things in general.
Vampire bats, native to Central and South America, feed exclusively in the wild on blood from live animals. If they go about 48 hours without a meal, they die. These bats have a strategy for staying alive when food is scarce. They can regurgitate blood in order to feed one another, though they won't do this for just anyone. They will only feed certain family and friends.
Carter can take Shiny out of the bat enclosure for a night and keep him in a separate cage where he doesn't eat. Then on his return to the other bats, he can observe whether any other bats are willing to feed Shiny. Vampire bats tend to have very strong relationships with their mothers and daughters and other close family. Investing in those relationships through grooming and just hanging out together tends to mean that those family members will reliably provide food when needed. But what happens if Shiny's mom isn't around?
The act of feeding is inherently more dangerous for vampire bats than it is for, say, fruit bats. A piece of fruit doesn't roll over and squish you. Vampire bats seek out animals that are asleep and use their ability to sense heat to figure out the best place to take a bite. That bite is risky. If it hurts, the animal might fight back....MORE
To readers who might be thinking of regurgitating a little blood sausage or black pudding for me, I appreciate the kind intention, I really do, but I'm good....Carter's conclusion is that there is a real advantage to making friends, but that advantage is only observed when a starved bat doesn't have access to close family.
“I definitely look at it from an economic viewpoint,” Carter says. “The idea of this paper is how does a bat make a decision about the number of relationships it creates and the strength of those relationships? The idea I have is that if your mom is your only food sharing partner and she dies, or isn't there when you need her, then you're screwed. So you should not be putting all of your eggs in one basket. It's like stocks. You should diversify. . . You don't just want to consider the return rate. You want to minimize risk, as well.”...