"Penguins are turning to prostitution. But instead of doing it for money, Antarctic dolly-birds are turning tricks to get rocks off their menfolk.
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On some occasions the prostitute penguins trick the males. They carry out the elaborate courtship ritual, which usually leads to mating.
Having bagged their stone, they would then run off. "
Full article here
http://news.bbc.co.uk/1/hi/world/asia-pacific/60302.stm