I notice that shadowbeasts are awake and active during daylight hours in Gothic 1. This makes them a lot harder in the early game, in comparison with G2 NotR where they are nocturnal, so that during daylight hours you have a chance of jumping to them and getting in a whack or two before they know what's going on.
I'm not sure if they sleep at nigh in Gothic 1, I don't like running around in the dark