(or Reason #12 for Women Not to get Married)
It is not just human males who seduce prospective paramours with expensive gifts while bringing home cheap trinkets for their long-term partners. Some male birds do it too.
Great grey shrikes mate for life and raise offspring each breeding season. But the males also sneak away and mate with other females. To charm both long-term partners and mistresses the males offer gifts of food.
Researchers in Eastern Europe then tested these males to see whether they put more effort into their "affairs" or their "marriages."
According to Piotr Tryjanowski at Adam Mickiewicz University in Poznan, Poland, and Martin Hromada at the University of South Bohemia in Ceské Budejovice, the Czech Republic, the male birds gave gifts to their mistresses which averaged 75 kiljoules of energy content, while gifts to their long-time partners only averaged 19 kilojoules.
Males often caught lizards, voles and other birds for their mistresses, which required six times as much effort to catch as the insects that they gave their partners.
Tryjanowski summed it up by recalling an old Polish saying:
"Artificial jewelery to the wife and real diamonds for the mistress."
(via New Scientist)