— Geirshnae can spawn anywhere in the southeast valley of Cliffs of Moher. That's a pretty big area. (See map below.)
— After he spawns he's restricted to a small roam area. (For an explanation of roam areas and spawn areas, click here.)
— He spawns shortly after dawn and despawns (disappears) at dusk.
— He doesn't spawn every day. It's not unusual for ten day-night cycles to pass before he spawns.
— You don't have to kill anything to make him spawn.