The habits of the shadowbeast

I think these monsters may be nocturnal, sleeping during the day. Not sure that this applies to all of them, but I visited the Cave of the Two Shadowbeasts beside the river on the road up to the Black Troll area. I arrived just before dawn, and both beasts were awake and moving. During previous play-throughs, I've found them sleeping and could surprise them, getting in that all-important preliminary whack.

Any thoughts? Thank you.