sentences:  Gilbert White studied the barn swallow in detail in his pioneering work "The Natural History of Selborne", but even this careful observer was uncertain whether it migrated or hibernated in winter.Elsewhere, its long journeys have been well observed, and a swallow tattoo is popular amongst nautical men as a symbol of a safe return; the tradition was that a mariner had a tattoo of this fellow wanderer after sailing .A second swallow would be added after at sea.