WHY PROVIDE FOR YOUNG THAT MAY NOT BE YOURS? Sparrows with unfaithful ‘wives’ care less for their young.

Sparrows form pair bonds that are normally monogamous, but many females are unfaithful to their partner and have offspring with other males. Biologists believe that the male birds are unfaithful to ensure that they father as many chicks as they can, while females are unfaithful with males of better ‘genetic quality’ – ones that are fitter and could produce stronger offspring.

However, cheating comes with a cost – the cheating female’s partner will provide less food for their nest of young. It has long been suspected that males know that not all the chicks in their nest are theirs, and so make a decision to provide less. But an alternative explanation is that cheating females and lazy males tend to pair up naturally.

Lessons for human relationships abound.