Data from: Food-sharing vampire bats are more nepotistic under conditions of perceived risk

Cooperative behaviors exist along a spectrum of cost, from no-risk
scenarios of mutual benefit to self-sacrificing altruism. Hamilton’s rule
predicts that as risk increases, cooperative decisions should become
increasingly kin-biased (nepotistic). To manipulate the perceived risks of
regurgitated food sharing in captive vampire bats, we created a novel
“rescue” condition, which required that donors leave their preferred
roosting location, descend to an illuminated spot on the cage floor, and
regurgitate food across cage bars to a trapped hungry bat. Vampire bats
adapted their food sharing to this novel context, but with a dramatic
reduction in the probability and amount of food sharing. Sixteen of 29
bats were fed by groupmates when trapped. All 15 starved bats that were
tested in both trapped and free conditions received less food when
trapped. Donations to trapped bats came from kin and nonkin, but subjects
received a greater proportion of their food from closer relatives when
trapped than when free. This finding supports the prediction that
nepotistic biases should be exaggerated under dangerous conditions.