Observing this vesper migration in different places, I began to see orderly segregation on a large scale. All the smaller herons dwelt together on certain islands in more or less social tolerance; and on adjoining trees, separated by only a few yards, scores of hawks concentrated and roosted, content with their snail diet, and wholly ignoring their neighbors. On the other side of the gardens, in aristocratic isolation, was a colony of stately American egrets, dainty and graceful. Their circumference of radiation was almost or quite a circle, for they preferred the ricefields for their daily hunting. Here the great birds, snowy white, with flowing aigrettes, and long, curving necks, settled with dignity, and here they slept and sat on their rough nests of sticks. When the height of homing flight of the host of herons had passed, I noticed a new element of restlessness, and here and there among the foliage appeared dull-brown figures. There occurred the comic explanation of white herons who had crept deep among the branches, again emerging in house coat of drab! These were not the same, however, and the first glance through binoculars showed the thick-set, humped figures and huge, staring eyes of night herons. As the last rays of the sun left the summit of the royal palms, something like the shadow of a heron flashed out and away, and then the import of these facts was impressed upon me. The egret, the night heron, the vampire--here were three types of organisms, characterizing the actions and reactions in nature. The islands were receiving and giving up. Their heart was becoming filled with the many day-feeding birds, and now the night-shift was leaving, and the very branch on which a night heron might have been dozing all day was now occupied, perhaps, by a sleeping egret. With eyes enlarged to gather together the scanty rays of light, the night herons were slipping away in the path of the vampires--both nocturnal, but unlike in all other ways. And I wondered if, in the very early morning, infant night herons would greet their returning parents; and if their callow young ever fell into the dark waters, what awful deathly alternates would night reveal; or were the slow-living crocodiles sleepless, with cruel eyes which never closed so soundly but that the splash of a young night heron brought instant response? XI THE BAY OF BUTTERFLIES