Penguin females have been observed trading sex for stones! These stones
are valuable to females because they are necessary for building nests.
Male penguins are known for being monogamous, so it is these females
that venture off to make some rocks by making some beds rock!
They typically target single males in order to avoid unnecessary
complications, however scientists believe the intercourse is not merely
for the stones because females would need to copulate with hundreds of
males in order to build a decent nest (they only take 1-2 stones each
time, and a nest requires hundreds!)
Scientists theorize that the females may be testing future mates in case their current partners happened to die.
