The term SEASIDE BIRD can be broken down into two crossword solutions, ERN (3 letters) and ERNE (4 letters). The ERN is a type of seabird that belongs to the family Laridae, which includes gulls, terns, and skimmers. It is a medium-sized bird with a black head, white body, and yellow bill. The ERNE is a species of large seabird belonging to the same family as the ERN. It is a large bird with a black head, white body, and yellow bill. It is usually found near coastal areas and feeds on fish, crustaceans, and other aquatic animals. Both the ERN and ERNE are common sights along the coasts of Europe, North America, and other parts of the world.