This one has been returning to the back of the bowl every 10 minutes or so and pecking on the bowl.
As you may be able to see the bowl is shiny and we were wondering if it was pecking at its reflection?
It pecks for a few seconds then jumps back onto the stone waits a few moments then returns to pecking the bowl. After three or so minutes it flies off low into the hedge.
We have looked and there does not seem to be any food there, in fact the bowl still contains fruit and nuts put out for the Badger and it makes no attempt to eat that.

Aren't all birds territorial? I'd always thought family groups have a territory and have to defend it against other families... not sure where I got that from though!

I think that Dunnocks tend to be more territorial during the breeding season, and that the size of their territory is influenced by food availability. We always have a number of Dunnocks in our garden, about 1/4 of the number of House Sparrows (which always seem to have been plentiful around here), and I've not witnessed any territorial behaviour - maybe because there's plenty of bird tables around?

Yes, they are territorial but you often see them going around in threes. This is because there are 2 popular ways for a male dunnock to pass on its genes :

a) attract a mate and defend a territory in the traditional manner
b) mate with another male's partner when he's not looking

Shockingly the females actually encourage option b!

Dunnocks specialise in feeding on very tiny prey, such as mites. So there might be more on the dish than you think. Or it could be reacting to its reflection, as most birds will in certain circumstances.