Vampire bats must feed on fresh blood at least once every 3 days or face starvation. Fortunately, friends share.
“Vampire bats have this ‘boom and bust’ foraging experience, so they either hit it big and get a large blood meal or they’re starved for that night,” explains American behavioral ecologist Gerald Carter.
Inexperienced young bats often fail to feed. They then desperately beg for a drink from those who have fed.
As they are noticeably bloated, well-fed bats are obvious to the less fortunate. If not apparent, bats rub bellies to see who is in a position to share.
Engorged bats often regurgitate blood to their begging friends, related or not. Bats remember favors, and practice reciprocal altruism. If a bat gives to another, but the favor is not returned at a time of need, the ingrate will be ignored in the future.
Amish in their sociality, selfish bats may be shunned when in need. Selfishness runs a considerable risk.
Bats are gregarious. Reputation matters.
Knowing the precariousness of their feeding situation, vampire bats develop lasting friendships via a well-worn mammal technique: mutual grooming. “Vampire bats selectively escalate low-cost grooming before developing higher-cost food-sharing relationships,” observes American bat behaviorist Rachel Page.
Sharing blood is an intimate transaction. It looks like a French kiss. “Food sharing in vampire bats is like how a lot of birds regurgitate food for their offspring,” says Carter.
Ishi Nobu, The Web of Life, BookBaby (2019).
Gerald G. Carter et al, “Development of new food-sharing relationships in vampire bats,” Current Biology (19 March 2020).
“Vampire bats form deep social bonds by grooming before sharing blood,” ScienceDaily (19 March 2020).