Don't do what I did!

Never sit against the tree they fly-up in!

I had roosted the flock the night before and did see them fly-up.

So I went and sat a bit closer - I got too close!

You can hear fly-ups as others have told you from quite some distance away. Listen for a short wing-beat, breaking branches and maybe a cluck ro two. But mainly the wingbeat and branch breaking. Just knowing you heard this you are father ahead than going to an area you think has birds. You know - you roosted them. Not toms? Okay are hens but Toms have to be clsoe by is my theory.

I try to shadow birds close to the timeto fly-up as I just sit known feeding areas. The birds will leave the field and start feeding in a direction and this will tell me where the roost is.
What I have found that the majority fly-up around 10 minutes before sunset plus or minus 15 minutes. Some earlier and some later. We even saw a group that dang near got run over by a car as it was jsut plain dark and well after sunset. One did need a flash light. But these birds wanted a specific roost. Was the latest I ever witnessed a fly-up.