A mutation is the collective noun for thrushes but is also applied to fieldfares and redwings which are part of the thrush family.

I was driving between Broughton and Stockbridge, late afternoon, when I suddenly found the bus completely surrounded by fieldfares! Look left and and see nothing but birds, look right and see the same, look ahead and see still more. I was driving at around 35 mph and they were flying at the same speed so it was almost as if they were still except movement was all around as the swerved left and right. Here’s a picture of a small flock which may give some idea of how they look but this flock was much bigger, I don’t want to exagerate the numbers but if there were less than 500 I’ll eat my hat!

The same area has decent sized flock of starlings also currently in residence but they are far fewer than the fieldfares.