Hopefully someone can help me with this. I was on a chalkland hill yesterday (Firle beacon, nr Lewes) when we heard lots of birds giving out a high pitch song. We couldn't see the birds until one of them landed on a fence post.
The bird was a bit bigger than a robin but smaller than a blackbird. Brown in colour but had two white flashes down it's tail when in flight. The songs were quite loud and highpitched and coming from the ground and one of the birds flew straight up into the sky flapping its wings quite fast (thought it looked like a bat the way it was flying.)