The esculent swallow (_Colocalia esculenta_)--whose edible nest, formed by a secretion which hardens in the air, is one of the greatest dainties of the Chinese epicure--may almost be considered as a sea-bird, as it chiefly inhabits marine caves in various islands of the Indian Archipelago, and exclusively seeks its food in the teeming waters.
[Illustration: ESCULENT SWALLOWS’ NESTS.]
The steep sea-walls along the south coast of Java are clothed to the very brink with luxuriant woods, and screw-pines strike everywhere their roots into their sides or look down from the margin of the rock upon the sea below. The surf of ages has worn deep caves into the chalk cliffs, and here the swallow builds her nest. When the sea is most agitated, whole swarms are seen flying about, and purposely seeking the thickest wave-foam, where no doubt they find their food. From a projecting cape, or looking down upon the play of waters, may be seen the mouth of the cave of Gua Rongkop, sometimes completely hidden under the waves, and then again opening its black recesses, into which the swallows vanish, or from which they dart forth with the rapidity of lightning. While at some distance from the coast the blue ocean sleeps in peace, it never ceases to fret and foam against the foot of these mural rocks, where the most beautiful rainbows glisten in the rising vapour.
Who can explain the instinct which prompts the birds to glue their nests to the high dark vaults of those apparently inaccessible caverns? Did they expect to find them a safe retreat from the persecutions of man? Then surely their hopes were vain, for where is the refuge to which his insatiable cupidity cannot find the way? At the cavern of Gua Gede the brink of the coast lies eighty feet above the level of the sea at ebb-tide. The wall first bends inwards, and then at a height of twenty-five feet from the sea throws out a projecting ledge, which is of great use to the nest-gatherers, serving as a support for a rattan ladder let down from the cliff. The roof of the cavern’s mouth lies only ten feet above the sea, which even at ebb-tide completely covers the floor of the cave, while at flood-tide the opening of the vast grotto is entirely closed by every wave that rolls against it. To penetrate into the interior is thus only possible at low water, and during very tranquil weather, and even then it could not be done if the roof were not perforated and jagged in every direction.