The most marked difference in the habits of the Adélie and the Emperor lies in the respective seasons at which each lays and incubates its eggs. Unlike the Adélie, which, as we have seen, chooses the warmest and lightest months of the year for the rearing of its young, the Emperor performs this duty in the darkest, coldest, and most tempestuous time. The only reason that has been suggested for this custom is that many months must pass before the chicks are fully fledged. Were they hatched in December (midsummer) as are Adélies, autumn would find them still unfledged, and probably they would perish in consequence, whereas, being hatched in the early spring, they are fostered by their parents until the warmer weather begins, and then have the entire summer in which to accomplish their change of plumage. [Illustration: Fig. 73. AN EMPEROR PENGUIN (Page 134)] The only Emperor rookery known to man at the present day was discovered by Lieuts. Royds and Skelton, of Captain Scott's first Antarctic expedition, on the sea-ice beneath Cape Crozier. Here in the dark days of July this extraordinary bird lays its one egg upon the ice. In the winter of 1911 a very brave journey was made to this spot by a party of Captain Scott's officers, consisting of Dr. Wilson, Lieut. Bowers and Mr. Cherry-Garrard. The experiences of this little band were so terrible that it is remarkable they ever returned to tell of them. Temperatures of -78° F. were encountered, and the most severe blizzards at lower temperatures than any sledging-party had yet endured. Under these truly terrible conditions the Emperors lay their eggs and hatch their young. The mortality under such circumstances is very high, as one would expect. Avalanches of ice fall from the cliffs above, crushing many of the parent birds, and causing hundreds of eggs to be deserted. As Dr. Wilson stated, the ice cliffs beneath which these remarkable animals sat were so unstable that no man in his senses would camp for a single night beneath them. In spite of this, evidence showed that after an avalanche of ice blocks from above, which had caused some of the Emperors to leave their eggs on the ice and bolt in terror, many of them had returned and continued to sit on the eggs which had been frozen and killed by the frost in their absence, continuing to do so long after they were completely rotten. Indeed, in their desire for something to hatch, some who had been deprived of their eggs, were seen to be attempting to incubate pieces of ice in their place, and, unlike Adélies, they seem ever ready to snatch and foster the young of their neighbours.