Condensed from an article by Michael Greshko, National Geographic, 17 November 2015
*Bats use a complex social calculus when they share regurgitated meals”.
*Vampire bats remember who has helped them”.
Vampire bats eat only blood—taking small amounts without harming their hosts, which include cattle, horses, chickens, and, of course, native wildlife – and have amassed remarkable biological features to do so. They have unique upper incisors evolved for rasping; they can sense body heat like a pit viper; they can run and jump; and they streamline weight loss from a blood meal by eliminating a blood meals’ water content within 30 minutes of eating – better for flying.
Female vampire bats care for their young for nine months—a long time relative to other bats – and they also help out their colony mates by sharing regurgitated blood with those unlucky enough to score a meal. This is an important behavior since a vampire bat missing two nightly meals in a row is likely to starve. Thus, the behavior is a probable example of reciprocal altruism—helping others so they’ll help you.
Gerald Carter, a student of University of Maryland biologist Gerald Wilkinson and now a researcher at the Smithsonian Tropical Research Institute in Panama worked with zoos to establish a captive population of several dozen related and unrelated common vampire bats (Desmodus rotundus) at the Organization for Bat Conservation in Michigan. He then observed them for three years, crouching in the bottom of their enclosure with a camcorder sensitive to infrared light.
Carter forced individual bats to fast for 24 hours. He then reintroduced those bats—both males and females—to the group, keeping track of which bats offered vomit snacks to their hungry comrades, recording which bats tended to share their meals with others. When he repeated this trial hundreds of times, Carter noticed that when a fasting female bat had previously shared her food with other females, she received more total sustenance than a selfish one. And some bats refused to help empty-bellied donors who had previously rebuffed them.
Carter also noticed that for many bats, getting denied a snack by an empty-bellied but otherwise willing donor didn’t doom the relationship. He noticed that donors who previously couldn’t give to their hungry neighbors gave even more once they had a meal to share, “just like how you might be especially generous to a friend if you were unable to help them for a long time,” says Carter.
The study suggests that female vampire bats keep track of whom they can turn to in a time of need—and actively work to repair relationships that have gone off-track. “Sharing meals is not just a one-off,” says Wilkinson, who was a co-author on the new study, published November 18 in Proceedings of the Royal Society B. “They integrate [social interactions] over a long period of time.”
Read the full article here.
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