Trill

In the fantasy series, "The Trinity Throne", a trill is a seabird that is the symbol of the ancient god Sygrid, worshiped by the Thaelfagen. The trill only appears along the coast of the Tjor Sea when low tide is approaching, and thus its arrival on shore is a symbol that a new throne heir is to be chosen to claim the Trinity Throne on Fjorgallahar.