WASHINGTON (AP) — Scientists have figured out why vampire bats are the only mammals that can survive on a diet of just blood.

They compared the genome of common vampire bats to 26 other bat species and identified 13 genes that are missing or no longer work in vampire bats. Over the years, those gene tweaks helped them adapt to a blood diet rich in iron and protein but with minimal fats or carbohydrates, the researchers reported Friday in the journal Science Advances.

The bats live in South and Central America and are basically "living Draculas," said co-author Michael Hiller of Germany's Max P...