Montreux Cormorant Festival

Everyone has heard of the Montreux Jazz Festival but today we saw a Cormorant Festival from the boat. It was extraordinary, at least double this number of birds was on and above the surface of the lake for no apparent reason. I wonder if they were flocking before leaving for the winter although I saw cormorants on the lake last winter, so do they leave?

I got to 75 birds in this part of the photo which is cropped significantly!