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The male serotine bat (Eptesicus serotinus) has a penis that, when erect, is around 22% of its body length. Credit: Joel Sartore/Photo Ark via NaturePL
Scientists have filmed what appear to be the first known instances of non-penetrative reproductive sex in mammals, in bats living in a church attic in the Netherlands and at a Ukrainian bat-rehabilitation centre. They wrote about their discovery this week in Current Biology1.
In most mammals — the group that includes bats and humans — fertilization of eggs happens internally and gestation also takes place internally. Males are thought to have evolved penises to deliver sperm close to the eggs during sex.
Other animals use alternative methods of reproduction. For example, songbirds mate by means of a specialized opening called the cloaca, which is also used for excreting waste. Sperm is transferred from the male birds to the females when they touch their cloacas together in a ‘cloacal kiss’.