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. In the past, the tolerance for this beneficial insectivore was reinforced by superstitions regarding damage to the barn swallow's nest. Such an act might lead to cows giving bloody milk, or no milk at all, or to hens ceasing to lay. This may be a factor in the longevity of swallows' nests. Survival, with suitable annual refurbishment, for 10–15 years is regular, and one nest was reported to have been occupied for 48 years.