You may have to click full screen, and use your imagination a bit, but its not hard to get the general jist of what they're up to, and they've been at it all bloody week. It all started off as harmless chasing, but is now starting to get out of hand, and I can't look out the window into the garden now without being confronted by some kind of sick avian sex act unfolding in front of my eyes.
In case you haven't studied the complicated reproductive behaviour of Dunnocks, just know that they don't do things the simple way. They have a tendancy to mix and match slightly during the breeding season, with females being happy to switch between males, and males not being shy to cater for more than one female. This can make things a little bit complicated when it comes to finding out who's fathering who's baby, so to maximise his breeding success, the male Dunnock will peck at the female's... ahhemm... to get her to release any... ahhemm... that another male may have... ahhemm... when backs were turned.
So next time you see a gang of drab, boring, brown little birds hopping innocently under your bird table, phone Jeremy Kyle. No doubt he'll be able to sort this kind of thing out.
God knows that they're up to as I write this...