I live in a terrace and have gutters front and back.
At the front the gutters overflow at one end and I had a sparrows nest in the roof at the other. A man came out today with a camera on a slick and said that my gutter at the blocked end was full of moss.
He is coming back to clean it next week. Just checking that this won't harm the sparrows in my roof at the other end (who should have flown by now anyway ...)
Not that I want sparrows in my roof - but neither do I want to harm them.