Spawns once the zone is completely emptied of other mobs. Four of them appear on the beach rocks at approximately:
(-270, -13, 1,165), near chest at water's edge
(-145, -19, 1,155), near the tents by the water
(-120, -12, 1,045), semi-near the zone entrance
(-195, -16, 1,085), also semi-near the zone entrance
The seagulls appear as NPCs; they have no "consider" information and are unattackable. Hailing them causes them to fly to the water's edge, where each one spawns an assassin snake that eats the bird.