For the food of petrels, strange to say, is oil. At any rate, nothing else is found in their stomachs, but where the oil comes from--whether they collect it from the surface of the sea, or whether by some chemical process of their own they convert other material into oil--no one can say with certainty. Oddly enough, too, the little stormy-petrel in its breeding haunts does not fly by day, but feeds its young at night; and here, again, reason is puzzled for an explanation. They lay their eggs in crevices of the rocks, in heaps of _débris_, or old rabbit-holes; but these are only to be found by searching, as there are no birds on the wing while the sun is shining, and they do not, like all others, betray their nurseries by going to and fro in the daylight with food. What strange contrasts! For more than nine months of the year the petrel is "the playmate of the storm"-- "Where the ocean rolls the proudest, Through the foam the sea-bird glides"-- always in attendance upon the tempest, an omen of ship-wreck and sea-terror: "The petrel telleth her tale in vain, And the mariner curseth the warning bird Who bringeth him news of the storm unheard;" and then for the rest of the twelvemonth it lurks in little holes in rocks, under heaps of stones, in rabbit-burrows, coming out only when it is dark, a bat-like creature of dusty crevices and dusky twilight, mortally afraid apparently of everything that moves by day, and shunning on land the men whom at sea it seemed to triumph over and to doom. And how terrible the declension from being "Mother Carey's chickens," mysteriously shaken out of the old dame's lap in the sky to bring men to their death by drowning, to "Blasquet chickens," picked out by ragged little islanders from the chinks in which they are hidden, and then eaten by tourists and townsfolk, fried upon toast! Nor are these birds' only enemies human ones, for in the predatory black-backed gulls they find untiring and cruel persecutors. As persistent and as cunning as crows, they loiter about the nesting-places of the smaller birds, searching out their eggs and young, and chasing the parents. Even large birds, like the cormorant, dare not leave their nests unprotected, as the air above is full of keen-eyed, black-backed gulls, and every eminence has its patient, sinister [Illustration: NEST OF LESSER BLACK-BACKED GULL] watchman waiting for some incautious mother to leave her eggs exposed, and in a twinkling the thief pounces on it.