My experience is that they don't see too well when it is dark. I have walked right under a roosting bird in the dark and didn't know it was there until it started to gobble at daybreak. When I am setting up on a roosting bird I usually get about 75 to 100 yards from it if it is dark and quiet walking. I try to set up between the bird and the nearest field since he will head that way as soon as he rounds up all the hens that are usually roosted there too. When I am in that situation I don't call much and let the birds work towards me. For the record most of my bigger birds have come late morning and are usually alone or with just a few hens. I find aggressive calling works best with them.