The Choral Society of the Hamptons will inaugurate its 70th anniversary season on Sunday at the Bridgehampton Presbyterian Church with performances at 3 and 5:30 p.m. Ottorino Respighi’s “Laud to the Nativity” will be the centerpiece of the program, which will also include shorter selections, among them medieval English carols, a Venetian polychoral work by Gabrieli, and Christmas music by composers including Vulpius and Praetorius.