Sailors, by and large, are very tidy people and like everything in place. Perhaps it was for this reason that in days gone by, when a bird was spotted where such a bird ought not to be, it was treated with the greatest of suspicion. Swallows were a case in point; if a passing swallow alighted on the rigging of a sailing ship, it was a sure sign of tempests on the way. Shakespeare alludes to such beliefs in Anthony and Cleopatra:
Swallows have built
In Cleopatra's sails their nests; the augurers
Say they know not, that they cannot tell, look grimly,
And dare not speak their knowledge.
Predictions by some other birds, however, were seen as friendly warnings, not conveyed with mischievous intent but merely indications that precautions must be taken.
Stormy petrel were credited with such benign intentions. They were sent for this purpose, it was said, by the Virgin Mary, always regarded as protectress of the mariner, and hence were called in French les oiseaux de Notre Dame. The English had similar ideas, but preferred to derive their petname for the stormy petrel from the Latin Mater cara, "beloved Mother", so the birds became known, with a touch of whimsy, as "Mother Carey's chickens". Other seafaring cultures focused on the wren. There was a sea-sprite, apparently, which was known to haunt the herring fisheries from time to time, and whose presence was always attended by a vicious storm; the storm would only abate when the sprite assumed the appearance of a wren and flew away.
Ancient mariners found it useful to smuggle a dead wren aboard the ship, presumably hoping the sight of a dead relative would frighten the stormy sprite away before it did its worst. But not all birds were harbingers of storms. The dove was well know to be the incarnation of the Holy Ghost. More importantly, perhaps, it was the creature which brought the good tidings of reemerging land to Noah when he had, perforce, become a mariner.
It was therefore looked on as the friend of sailors everywhere, and a dove perching on the mast or rigging of a sailing ship was an omen of a peaceful, favourable voyage, with no gales and just the right amount of wind. But perhaps the wisest precaution for any sailor was always to drive his spoon through the egg-shell after eating his boiled egg. Failure to do so ran the risk that a passing witch might use the eggshell as a boat, going to sea in it to brew up storms and other torments for the careless mariner.