The poet Oliver Goldsmith was not normally given to ornithological pronouncements. He devised, however, an interesting theory as to how albatrosses sleep. Diomedea exultans, the wandering albatross, roams the empty vastness of the southern oceans, and can stay aloft for hours, or even days, while scarcely moving its long, slender wings.
It needs wind, however, to support its way of life; its physical structure is ideally suited to "dynamic soaring" in the strong steady breezes of the middle latitudes of the southern hemisphere, the so-called Roaring Forties.
Indeed, generations of seafarers in those parts noticed that wherever the albatross might be, the wind was, too, so its presence in olden times was taken as an indication of favourable conditions that would speed the sailor on his way.
Close to the surface of the water, the roughness of the sea disturbs the flow of wind. Diomedea takes advantage by gliding down towards the waves at a shallow angle, and then shearing up again, using the turbulent air-flow to gain height in much the same way as a seagull exploits the up-draughts caused by a breeze encountering a cliff.
Given this relaxing, yet perpetually mobile, way of life, perhaps it is not surprising that people have wondered from time to time if these birds ever manage to take any sleep.
Goldsmith's theory was a novel one: "At night, when they are pressed for slumber, they rise into the clouds as high as they can; putting their head under one wing they beat the air with the other, and seem to take their ease."
How he came to this conclusion is not told, but in any case more reliable observers have noted that the bird chooses to rest on the ocean during calms, and that in any event, Diomedea is so aerodynamically efficient that it can afford to nod off while on the wing without catastrophe. Nowadays, albatrosses have more serious problems than simply seeking 40 winks. To an increasing extent, and sufficiently to endanger their survival as a species, the birds are thought to be falling foul of the long lines, armed with thousands of baited hooks, that are trailed behind commercial fishing boats.
Despite the fact that they may live for 60 years, albatrosses have a slow rate of reproduction. They do not begin to breed until the age of nine or 10, and then each pair produces only one chick every two years on average.
There are fears, therefore, that the combination of the fishing boats' long lines and their own slow rate of breeding may ultimately threaten the very existence of Diomedea exultans. .