As I strolled through the rookery, most of the birds took little or no notice of me. Some, however, swore at me very savagely, and one infuriated penguin rushed at me from a distance of some ten yards, seizing the leg of my wind-proof trousers. In the morning quite a large number lay down on the sea-ice, a few yards short of the rookery, content apparently to have got so far. They lay there all day, motionless on their breasts, with their chins outstretched on the snow. By the evening of October 18 most of the penguins had gathered in little groups on the nest-covered eminences, but there was at that time ample room for all, there being only about three or four thousand arrived. Although there were several open water holes against bergs frozen into the sea-ice some half mile or so away, not a single bird attempted to get food. At 6 P.M. the whole rookery appeared to sleep, and the ceaseless chattering of the past hours gave place to a dead and impressive silence, though here and there an industrious little bird might be seen busily fetching stone after stone to his nest. At that date it was deeply dusk at midnight, though the sun was very quickly rising in altitude, and continuous daylight would soon overtake us. [Illustration: Fig. 11. THE ROOKERY BEGINNING TO FILL UP (Page 18)] By the morning of October 19 there had been a good many more arrivals, but the rookery was not yet more than one-twentieth part full. All the birds were fasting absolutely. Nest building was now in full swing, and the whole place waking up to activity. Most of the pebbles for the new nests were being taken from old nests, but a great deal of robbery went on nevertheless. Depredators when caught were driven furiously away, and occasionally chased for some distance, and it was curious to see the difference in the appearance between the fleeing thief and his pursuer. As the former raced and ducked about among the nests, doubling on his tracks, and trying by every means to get lost in the crowd and so rid himself of his pursuer, his feathers lay close back on his skin, giving him a sleek look which made him appear half the size of the irate nest-holder who sought to catch him, with feathers ruffled in indignation. This at first led me to think that the hens were larger than the cocks, as it was generally the hen who was at home, and the cock who was after the stones, but later I found that sex makes absolutely no difference in the size of the birds, or indeed in their appearance at all, as seen by the human eye. After mating, their behaviour as well as various outward signs serve to distinguish male from female. Besides this certain differences in their habits, which I will describe in another place, are to be noted.