ultrafacts:

Vampire bats are bats whose food source is blood, a dietary trait called hematophagy.

Vampire bats share a strong family bond with members of the colony, which is believed to be why they are the only bats to take up this adoption characteristic. Another unique adaptation of vampire bats is the sharing of food. A vampire bat can only survive about two days without a meal of blood, yet they cannot be guaranteed of finding food every night. This poses a problem, so when a bat fails to find food, it will often “beg” another bat for food. The “host” bat may regurgitate a small amount of blood to sustain the other member of the colony. This has been noted by many naturalists as an example of reciprocal altruism in nature.  

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