Identifying a roost area with documented occurrences could be really important to long term habitat protection.
A nighttime roost is usually a collection of larger trees that provide some kind of thermal protection (usually, but not always).

Basically, watch for the location they go in late afternoon (around 3 PM to dark) and count them as they fly or make short shifts into that location.

If you suspect you know the overnight location already, situate yourself where you can see them leave the roost starting about 30 min before dawn. Most fly out of the roost to go hunting in the first 60-90 minutes. (On very cold days, some may remain in the roost.)
The goal of the roost survey is to map the area where the birds are actually spending their overnight. Such documentation could be very important for maintaining some habitat protection for this area! less ↑