I assume you start at dawn and move it from there, so you get more light as thing go, which helps. On that kind of terrain (Monterenzio) a few years ago I was spotting a female red deer + her fawn at about 1450 metres away at dusk, with the 80mm swaro on a tripod and that was not a super clear ID because of the light -- I kind of knew it was a red deer, but they are not at all common there and the image was not good enough to overcome my surprise and put the thing to rest (also I measured the distance after so I could not get a good feel for the actual size of the animal). Had it been a stag, no way I could have looked at the antlers and made a decision to cull or not. Which basically means, if the light is bad, forget about it, even on a tripod, if you have a light scope. Roes, with their small antlers would be hard to tell males and females apart at a distance if the image is not super crisp.