When you dock at Thamur’s Corpse, you’ll see a Mystic Gateway to your left. Stand in the corner here and look up at the cliff to spot the first Raven.
Thamur’s Corpse #2
Head to the Hidden Chamber near the dock once you acquire the Magic Chisel. Take the elevator down and defeat the Valkyrie [Gunnr] at the bottom. Check the tree in the center upon her death to find the Raven.