TROPICAL SEA-BIRDS 305 



along, most frequently without any motion of their outstretched 

 ])inions, but at times this smooth progression is interrupted 

 by sudden jerks. When they see a ship, they never fail to sail 

 round it, and the mariner bound to the equatorial regions, hails 

 them as the harbingers of the tropics. The two long straight 

 narrow feathers of which their tail consists, are employed by 

 the natives of the greater part of the South Sea Islands as 

 ornaments of dress, and serve to distinguish the chieftains from 

 ilie multitude. 



The esculent swallow {Golocalia 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. 



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 

 Eongkop, 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 light- 

 ning. 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 



I hopes were vain, for where is the refuge to which his greedi- 



1 ness cannot find the way ? At the cavern of Gua Gede the 



j 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 



