As a teacher once told me, “There’s no such thing as a seagull.”
The word seagull is an informal way of referring to any of the species that belong to the family Laridae, the gulls. There are common gulls, herring gulls, glaucous-winged gulls, Pacific gulls, etc. But there is no species called a seagull. Just call them gulls. Although they are associated with marine environments, many species live much of their lives inland.