E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
The largest of web-footed birds, called by sailors the Cape Sheep, from its frequenting the Cape of Good Hope. It gorges itself, and then sits motionless upon the waves. It is said to sleep in the air, because its flight is a gliding without any apparent motion of its long wings. Sailors say it is fatal to shoot an albatross. Coleridges Ancient Mariner is founded on this superstition.