Crow v Magpie

I saw an amazing confrontation between a crow and a magpie today. I think it was the magpie that was defending its nest against a crow. The crow was much bigger than the magpie but the magpie was using gerrila tactics against it. The crow seemed to be in control but while it was right beside the nest it did not seem to risk going in to take whatever it was after.

Eventually the crow flew down to the pavement and the magpie went back to its nest.

Has anyone seen behaviour like this before?