and striking applications of the same principle occur among bright-colored 

 land birds, notably tropical ones. There are species with almost the entire 

 plumage highly iridescent, changing perhaps from bronzy red to emerald 

 green (or even to blue), according to the bird's position relative to the source 

 of light and the beholder. Such for instance are some of those exquisite 

 aberrant kingfishers, the jacamars (Galbulidce) of South America. One of them 

 at least, Galbula ruficauda, the only kind my father and I have studied in 

 its native forests, is exceedingly hard to discover when it is sitting stock- 

 still on its exposed look-out perch low down among the trees. It affects 

 semi-cleared areas, and the open reaches and borders of the forest, where 

 there is much variety in the colors of its background, and there is no dis- 

 puting the fact that its beautifully rich iridescence aids it greatly in escaping 

 notice in these places. Its colors shift with the shifting scene, as it were; 

 they counterfeit the airy life and changefulness of the encompassing leafy 

 landscape, played on and vivified by wind and sun and shadow, not to speak 

 of the changes wrought by the movements of the beholder. The environing 

 landscape contains, in one or another degree of purity and brilliance, all the 

 colors of the rainbow; and the tints of the jacamar's plumage likewise range 

 through almost the entire spectrum. Often the bird's background is bluish 

 green, often all his upper parts show nothing but that color; often, again, his 

 background is rich reddish bronze, just such as his feathers show in certain 

 other lights, and so on. Of course the changes in the bird's color are inde- 

 pendent of the changes in his background, but in the long run his lively versa- 

 tility of tint must enable him much oftener to match his versatile background, 

 in part at least, than he could if his colors were unchanging. The jacamar is 

 also a bird of the deep forest, however — not by any means confined to the 

 bright-colored half-open regions — and accordingly he wears on his underside 

 the regulation forest brown of tropical woodland animals. (See Chapter 

 XIX, p. 107.) If a bird wears colors characteristic of his environment, it is 

 not necessary for his concealment that he should momently 'match' his back- 

 ground, even in part. A spot of brown, for instance, introduced where such 



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