Vampire bats share meals with roost mates who have fed them before
A vampire bat that returns hungry can be saved by a roost mate regurgitating blood for it. Studies in Costa Rica found this sharing depends on long friendships and repayment: the best predictor of how much one bat gives another is how much it has received in return, a pattern also seen among primates.
The common vampire bat lives from Mexico through Central and South America down to Uruguay, northern Argentina and central Chile. Small, averaging 9 centimetres long with an 18-centimetre wingspan, it weighs roughly 25 to 40 grams, though a single meal can make it much heavier. It has the fewest teeth of any bat, and its upper incisors lack enamel, which keeps them razor sharp.
At night it tracks sleeping animals by echolocation and smell, preferring livestock and choosing horses over cattle when possible. Heat sensors in its nose locate blood vessels near the skin, it cuts a small flap with its teeth, and laps the flow with a grooved tongue while an anticoagulant in its saliva, named draculin, keeps the wound open. Unlike most bats it moves well on the ground, running with a bounding gait powered by its wings rather than its weak legs, using pads under each thumb like soles.
Its social life is intense. Females usually stay in the group where they were born, and mutual grooming strengthens bonds; researchers have suggested a groomer may even judge from a partner's belly whether it truly needs food. In the field study run from 1978 to 1983, 70 percent of observed sharing was mothers feeding pups, and nearly all the rest went to close relatives. Yet how often two bats associated explained sharing better than kinship alone, and it appeared only between bats that roosted together more than 60 percent of the time.
The species also carries rabies, a danger chiefly to cattle. Joseph Lennox Pawan, a government bacteriologist in Trinidad, identified the first infected vampire bat in March 1932 and showed bats could spread the virus without appearing ill, a claim first ridiculed as fantastic. Despite its pest status, the IUCN lists it as least concern.
Source: Common vampire bat
