Cormorants in unfamiliar enviroments?

I think I saw a cormorant in the trees near our house, but cormorants live by the sea. We live a long way for a cormorant to fly to. Then, there's the possibility that it was not a cormorant. A rare species of black heron is a possibility. We usually see a grey heron, so why not other herons in the surrounding area? If it is a heron, then is probably a migrant, as black herons are more common in mainland Europe, than Britain.

There's also the theory that it is some kind of cormorant-shaped crow. If it is, then it must be a new species. I think there might have been other sightings of this sort, so I will have find more information about them.

It maybe one of these, or something completely different. I may never know.