The most thickly populated districts were to be found on the screes immediately below the cliffs. These screes having been formed in the first instance by the falling of fragments due to weathering of the cliff, their substance is still added to, little by little, as time goes on, and therefore many are killed annually by falling rocks, as is mentioned elsewhere, but weighing against this danger is the advantage the cliff offers as a shelter from the E.S.E. gales. The same applies to the nesting sites up the cliff, but I am convinced that only the love of climbing can account for the extraordinary positions chosen by some of the birds. Some of the nests are so difficult of access that their occupants, on their way to them, may be seen sliding backwards down the little glazed snow-slopes several times before they accomplish the ascent, whilst in other places they have to jump from one foothold to another along the almost perpendicular cliff. Even up these heights a tendency to grouping is seen, though there are a fair number of individuals who, seeming to seek seclusion, make their nests at some distance from the others. I noticed this in some places along the shore, too, where solitary nests were to be seen on isolated patches of shingle. When I visited Cape Royds in 1911 I found a couple nesting alone in a cove known as "Black Sand Beach," some half mile from the rookery there. Such isolation as this, however, is very unusual, and was quite a departure from the regular custom of the species. [Illustration: Fig. 44. "WHEN THEY SUCCEEDED IN PUSHING ONE OF THEIR NUMBER OVER, ALL WOULD CRANE THEIR NECKS OVER THE EDGE" (Page 83)] In some places at Cape Adare, large rocks some two or three feet in height stood about the rookery. Whenever the summit of one of these was accessible, a pair built their nest upon it,(4) though how they managed to keep up there during the gales was a matter for wonder, but the proud possessors of the castle evidently had a delight in their lofty position. One nest had been made on an old packing-case left by the expedition which wintered there in 1894, and several nested among the weathering bones of the seals that had died on the beach. (4) Fig. 37. Although the greatest care had been taken by nearly all in the choice of sites that would be on dry ground when the thaw came later in the season, yet a few hens had gone to the other extreme, and with greatest stupidity chosen their site right down in the hollows where they were absolutely certain to be flooded later on. These stupid ones are thus prevented from rearing their young, and so selection keeps the wiser for future generations, and eliminates the less intelligent from the community, though perhaps some of these learn by experience, and next year use more discrimination in choosing their nesting place.