Female serotine bats have a large membrane between their tail and ankles which they can use to shield their genitals.

During mating, the males grab the females by the nape and use their large penises like an extra arm to reach around and remove this membrane, the researchers said.

Then follows a long, still embrace called "contact mating," during which sperm is transferred.

While this form of reproduction — also called "cloacal kissing" — is common in birds, it had never previously been observed in a mammal.

For serotine bats, the process takes some time. The average session was 53 minutes, but the longest lasted nearly 13 hours.