Researchers from the Federal University of Pernambuco are baffled after they discovered that the nocturnal vampire bats in Brazil, which were thought to feed only on bird and small mammals like pigs, have started sucking human blood!

Feces samples from 70 of the blood-suckers living in the Catimbau National Park in Brazil were tested and three showed traces of human blood, stunning researchers.

“We were quite surprised,” Enrico Bernard, the lead author of the study, told the New Scientist, adding that some bats also fed on chickens. “This species isn’t adapted to feed on the blood of mammals. They are adapting to their environment and exploiting the new resources.”

Human blood, like that of all mammals, is difficult for bats to process because it has a thicker, high-protein content than birds. In other studies, vampire bats starved to death before trying to drink pig or goat blood.

The results of the study are worrying to researchers, who believe human intrusion — and therefore a lack of birds — into the park is the root cause, because bats transmit diseases such as rabies.

“This opens a range of research possibilities on vampire bats in the Caatinga (region), both on the species’ biology and the consequences for public health, considering the potential increase in the transmission of rabies in the region,” the study concluded.