a spot might well occur in the background, will readily pass for a real back- 

 ground-detail. 



There are two kinds of changeable color among birds. One is iridescent 

 or metallic color, such as we have been considering, and the other, worn by- 

 many of the most gorgeous species, is what may be called 'dead' or sheen- 

 less, changeable. In this there is no sudden glinting or intricate intershifting 

 of bright colors, but merely a change in the general tint of the lusterless and 

 uniformly-colored surface, dependent on the complete change of its position 

 relative to the source of light. This kind of coloration lacks all the subtler 

 ma^ic of obliterative power possessed by iridescence, but shares to some ex- 

 tent its advantage of adaptability to often-varied backgrounds. Many of the 

 most brilliant blues, greens, and purples in the plumage of birds are of this 

 lusterless type. Good examples among familiar species are the common 

 European Kingfisher (Alcedo ispida), and the North American Indigo Bunt- 

 ing {Passerina cyania). When such a bird is between the beholder and the 

 source of illumination, its brightest color is a deep blue, or sometimes even 

 purple. When, on the contrary, the beholder has the source of illumination 

 behind him, and the bird in front, so that the light, striking it fully and fairly, 

 is reflected directly back to the eye, the parts which were before dark blue or 

 pyrple are clear, light green, sometimes even golden green or almost yellow. 

 (For the best effect, particularly in the display of the green extreme, the bird 

 should be seen head-on.) Some birds which are wonderfully inconspicuous 

 in their normal haunts have this type of coloration. Such for instance is the 

 American Purple Gallinule {lornis mariinica), mentioned in an earlier chap- 

 ter. The changeableness of this bird's color, however, is mainly from bright 

 to dim, rather than from green to purple, and does not play a very important 

 part in his 'disguisement,' which is nevertheless adequate. It consists in a 

 close imitation of the beautifully blended tints of quiet water amidst luxuriant 

 vegetation. The soft purple breast and sides picture that part of the pool 

 which is shaded from the sky, and reflects almost nothing; the bright-blue 

 wing depicts the water which reflects the sky, and the green and olive back. 



91 



