A murder of crows

A couple of days ago we were just getting ready to head home because it was already getting dark.
Suddenly I heard lots of squawking and looked up to see hundreds of crowd circling around directly above.
Today there was a lovely sunset.....

..... and then a few minutes later the crows started to appear again.

It reminded me of the huge numbers of starlings that we used to see in Brighton that was called a murmuration.
I have looked online and a group of crows is called a 'murder'.
In the olden days it was a small step from seeing them as scavengers to thinking of them as a huge gang that actually hunted down and killed their foes.
I think that just to be on the safe side I will keep the greenhouse door closed in future.