AILSA CHANG, HOST:
It is Halloween, a night when you expect to see witches, ghosts and vampires - all just pretend ones, of course. But in real life, there are scientists who study vampires - vampire bats, that is. NPR's Nell Greenfieldboyce reports on a new study that reveals the warm, fuzzy side of these bloodthirsty little beasts.
NELL GREENFIELDBOYCE, BYLINE: A common vampire bat doesn't actually suck blood; it uses its teeth to make a small cut on, say, a cow. Then it laps at the wound, drinking about a tablespoon of blood.
GERRY CARTER: They need to do this basically every night. So if they miss two nights, they're very weak. If they miss three nights, they will probably die.
GREENFIELDBOYCE: Gerry Carter is a researcher at The Ohio State University. He says a desperately hungry bat isn't hopeless because back at the hollow tree or wherever it lives, it can find fellow bats who are willing to regurgitate a bit of their last bloody meal so that the other can eat.
CARTER: The females all do this for their offspring, but they also do it for adults, including unrelated adults.
GREENFIELDBOYCE: And adult bats that share food with each other develop bonds. Carter has studied this in common vampire bats that he captured in Panama and kept in the lab.
CARTER: We can just take a bat, deprive it of food for a while, put it back and then see who is willing to share food with it. And we can just do this repeatedly over time.
GREENFIELDBOYCE: Certain pairs of bats were more likely to share food back and forth. They became buddies. Carter watched these relationships strengthen over time in about two dozen female bats that he kept for nearly two years. Just before these bats were released back into the wild, the researchers glued on tiny sensors. For over a week, the sensors checked each bat's proximity to all the other tagged bats every two seconds. In the journal Current Biology, the researchers report their findings - bats that were close pals in captivity generally continued to hang out, even when they were free to fly anywhere.
SARAH BROSNAN: The study's fascinating.
GREENFIELDBOYCE: Sarah Brosnan wasn't part of this research team; she studies social relationships in animals at Georgia State University.
BROSNAN: If a bat can have a friend or have an associate or maintain these relationships - or whatever you want to call it - then that suggests that maybe it doesn't require as much cognitive capacity as we've typically assumed.
GREENFIELDBOYCE: She says a word like friendship can be controversial when it comes to animals.
BROSNAN: But I think a case could be made that it is a friendship with the appropriate caveats applied.
GREENFIELDBOYCE: Those caveats being that, for vampire bats, friendship mostly involves hanging together in the dark and sharing the taste of blood.
Nell Greenfieldboyce, NPR News.
(SOUNDBITE OF PRINCE SONG, "BATDANCE")
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