I've since figured out the behaviour of the bridge drake. After you rest at a bonfire and trigger monster respawn, if the drake is not sitting on the parish, then when you walk to the Solaire-end he'll strafe the whole thing and take up residence. Conversely, if the drake is already squatting and you enter the bonfire room, it scares him away.
This episode also features 1,000 Balder Knights.
