Seagull attempting to ward off a heron

So I was sat out the back of my work having a smoke, a heron landed in front of me which I thought was pretty cool.. So I sat there, not much longer later a seagull was freaking out as it flew past and started to swoop down at the heron as if trying to ward it off. The seagull must have felt threatened by the heron. But the heron didn't really seem too bothered by it.

The heron must have been sat there waiting for fish? As that is a flooded dock where a lot of fishing takes place.