So the rule females are following is: find the best male she can as a partner with the sub-rule, depending how good hubby is, try to find really good males for affairs and risk getting caught. Meanwhile males follow a different rule: find the best female they can as a partner, plus as many females as possible for affairs, while still feeding wife and family enough to survive with sub-rule if partner cant be trusted, invest even more energy in having affairs and less in feeding marital nest.

One thing is clear, when you see a pair of blue tits trekking back and forth to their nest from your bird table, taking turns to feed their little ones, don't be deceived. You're not witnessing a picture of perfect family harmony, rather the tip of a seething mass of intrigue and double-crossing, the battle of the sexes played out in miniature.