Vampires Take Over Costa Rica

You think we're making this up, don't you? Well we're not. Real, blood-sucking vampires are multiplying and spreading all over Costa Rica and Central America. And they are dining well. They're eating cow blood.

There have never been this many vampire bats before.

Farmers have observed vampire bats attacking cattle recently. (Vampire bats only feed on humans in rare instances.)

To see if the farmers were right about the overall trend in bats' new diets, Christian Voigt of the Leibniz Institute for Zoo and Wildlife Research in Berlin and colleagues measured isotopes in exhaled carbon dioxide in both captive and wild vampire bats.

“The potential victims of vampires in Costa Rica are either cattle or rainforest mammals such as tapirs and peccaries," Voigt said.

The two animal groups feed on different plants with distinct levels of carbon isotopes. "Therefore, we expected that the stable carbon isotope signature in bat breath would change according to their diet,” Voigt said.

The bat breath showed the chemical marks of cattle, indicating, the authors say, that the last blood meal of the flying mammals almost always was cattle.

But when the farmers figure out how to protect the cows, the abundance of bats will have to look elsewhere for dinner. We wouldn't plan any trips to Costa Rica for the foreseeable future.