February 14 is a day for kisses, hugs and celebrating love with the help of flowers, balloons and chocolates. However, a keen observer of nature, following the customs of Homo sapiens, would quickly come to the conclusion that every year the holiday of lovers involves some reshuffling of partnerships. And this is by no means evidence of our weakness or wickedness – even waterfowl, which have been prized for decades for their undying fidelity, are proving to have their own definition of monogamy.