THE HUMMING BIRDS. 307 



CAUSE OF THE CHANGEABLE HUES OF HUMMING BIRDS. 



Many persons may naturally wish to know the cause or causes of this 

 brilliant metallic coloration of Humming Birds. This is a subject which 

 has been investigated by physiologists, who have found that in most 

 cases it depends on the structure of the feathers, and not on the pres- 

 ence of coloring matter or pigment. 



A few days since [says Mr. MartitiJ we were ex-iimning a Humming Bird, the gor- 

 get of which was an intense emerald -green ; but on changing the light (that is, alter- 

 ing its angle of incidence), the emerald was changed to velvet-black. Andebert con- 

 sidered this chacgeableness to be due to the organization of the feathers, and to the 

 manner in which the luminous rays are reflected on falling upon them ; and of this 

 we think there can be little doubt, for each feather, when minutely inspected, ex- 

 hibits myriads of little facets so disposed as to present so many angles to the incidence 

 of light, which will be diversely reflected according to the position of the feather, and 

 in some positions not reflected in any sensible degree, and thus emerald may become 

 a velvet-black. Lesson supposes that the brilliant hues of the plumage of the Hum- 

 ming Birds are derived from some elements contained in the blood, and elaborated by 

 the circulation a theory we do not quite understand, inasmuch as color is the result 

 of the reflection of some rays and the absorption of others, caused by the arrange- 

 ment of the molecules of any given body. He adds, however, that the texture of the 

 pluoies plays the principal part, -in consequence of the manner in which the rays of 

 light traverse them or are reflected by the innumerable facets which a prodigious 

 quantity of barbules or fibers present. All the scaly feathers, he observes, which 

 simulate velvet, the emerald, or the ruby, and which we see on the head and throats 

 of the Epimachi (as the Grand Promerops of New Guinea), the Paradise Birds and 

 the Humming Birds resemble each other iathe uniformity of their formation; all are 

 composed of cylindrical barbules, bordered with other analogous regular barbules, 

 which in their turn support other small ones; and all of them are hollowed in the 

 center with a deep furrow, so that when the light, as Audebert first remarked, glides 

 in a vertical direction over the scaly feathers, the result is that all the luminous rays 

 are absorbed in traversing them, and the perception of black is produced. But it is 

 no longer the same when the light is reflected from these feathers, each of which per- 

 forms the office of reflector; then it is that the aspect of the emerald, the ruby, etc., 

 varying with the utmost diversity under the incidences of the rays which strike them, 

 is given out by the molecular arrangement of the barbules. It is thus that the gor- 

 get of many species takes all the hues of green, and then the brightest and most uni- 

 formly golden tints, down to intense velvet-black, or on the contrary that of ruby, 

 which darts forth pencils of light, or passes from reddish orange to a crimsoned red- 

 black. It is thus we think that the everchaugiug hues of the gorgets of the Hum- 

 ming Birds from black to emerald, ruby, crimson, or flame color are to be explained. 



Brilliant, however, as are the hues reflected from the stuffed Hum- 

 ming Bird, the perfection of their changeable radiance or refulgence 

 can be fully realized only in the living bird. 



Bullock, when speaking of the same subject, says that u the pre- 

 served specimens were but the shadow m brilliancy to what they were 

 in life. The reason is obvious; for the sides of the lamina or fibers of 

 each feather being of a different color from the surface will change 

 when seen in a front or oblique direction ; and as each lamina or fiber 

 turns upon the axis of the quill the least motion, when living, causes 

 the feathers to change suddenly to the most opposite hues," 



