Dunnock (Prunella modularis)

The Dunnock has a socially complex lifestyle.  Often nesting in groups, with one dominant pair.  The group has mixtures of both females and males, and at times the female can pair with a subordinate male who assists with the nesting process, although she actually mates with the dominant male.  When chicks hatch, the male who is the natural father assists the female with the feeding.

Some males are polygamous, some females are polyandrous.  The whole system can be is chaotic, anything goes!