Parrakeets whirl roostwards with machine-like synchronism of flight; geese wheel down in more or less regular formation; but these herons concentrated along straight lines, each describing its individual radius from the spot where it caught its last fish or shrimp to its nest or the particular branch on which it will spend the night. With a hemicircle of sufficient size, one might plot all of the hundreds upon hundreds of these radii, and each would represent a distinct line, if only a heron's width apart.
At the height of the evening's flight there were sometimes fifty herons in sight at once, beating steadily onward until almost overhead, when they put on brakes and dropped. Some, as the little egrets, were rather awkward; while the tricolors were the most skilful, sometimes nose-diving, with a sudden flattening out just in time to reach out and grasp a branch. Once or twice, when a fitful breeze blew at sunset, I had a magnificent exhibition of aeronautics. The birds came upwind slowly, beating their way obliquely but steadily, long legs stretched out far behind the tail and swinging pendulum-like whenever a shift of ballast was needed. They apparently did not realize the unevenness of the wind, for when they backed air, ready to descend, a sudden gust would often undercut them and over they would go, legs, wings, and neck sprawling in mid-air. After one or two somersaults or a short, swift dive, they would right themselves, feathers on end, and frantically grasp at the first leaf or twig within reach. Panting, they looked helplessly around, reorientation coming gradually.
At each arrival, a hoarse chorus went up from hungry throats, and every youngster within reach scrambled wildly forward, hopeful of a fish course. They received but scant courtesy and usually a vicious peck tumbled them off the branch. I saw a young bird fall to the water, and this mishap was from no attack, but due to his tripping over his own feet, the claws of one foot gripping those of the other in an insane clasp, which overbalanced him. He fell through a thin screen of vines and splashed half onto a small Regia leaf. With neck and wings he struggled to pull himself up, and had almost succeeded when heron and leaf sank slowly, and only the bare stem swung up again. A few bubbles led off in a silvery path toward deeper water, showing where a crocodile swam slowly off with his prey.
For a time the birds remained still, and then crept within the tangles, to their mates or nests, or quieted the clamor of the young with warm-storage fish. How each one knew its own offspring was beyond my ken, but on three separate evenings scattered through one week, I observed an individual, marked by a wing-gap of two lost feathers, come, within a quarter-hour of six o'clock, and feed a great awkward youngster which had lost a single feather from each wing. So there was no hit-or-miss method—no luck in the strongest birds taking toll from more than two of the returning parents.
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?