Hi Bud

Dunnocks have adapted to make use of different breeding strategies. Both males and females want make sure their genes are passed on to the next generation. Where food is plentiful, territories need not be so big, and so there's less opportunity for overlap with those of other birds. Where life is tougher, the territories need to be bigger and that means more interaction with other Dunnocks.

However, what works for one pair of Dunnocks might not work for another. There are several different strategies they might use:
   A male paired with a female (monogamy)
   More than one male paired with the same female (polyandry)
   A male paired with more than one female (polygyny)
   'Pairs' with two males and two females (polygynandry)

And it's all going on in your shrubbery...