THE METALLIC COLORS OF FEATHERS FROM THE 

 NECK OF THE DOMESTIC PIGEON. 



R. M. STRONG. 



The so-called metallic colors and iridescent effects exhibited by 

 many feathers have been variously explained by different writers. 

 In general they are recognized as diffraction phenomena peculiar 

 to the barbules. 



If one observes the neck of a gray domestic pigeon by reflected 

 sunlight, the feathers on the sides will appear bright metallic- 

 green when the angles of incidence and reflection are small. 

 But when the angles are large, the same region has a purplish 

 appearance. Under other conditions a dull brown color prevails. 

 A single feather gives metallic colors only from the distal 

 exposed portion. 



The hypotheses based on the supposed presence of striae or 

 ridges, supported by Haecker ('90) and others are seen at once 

 to be inapplicable to this case when one finds that the feather 

 may be rotated through a whole circle with essentially the same 

 color effects for given angles even from individual barbules. Fur- 

 thermore, a careful microscopic study of the barbule surface shows 

 that irregularities such as striae, ridges, pits, knob -like eleva- 

 tions, etc., are not frequent enough when sufficiently small to 

 produce grating effects, and in fact are not normal occurrences. 



On comparing barbules giving metallic colors with barbules 

 from the same barb in a region of non-metallic colors, striking 

 modifications are found. The barbules from the region where 

 metallic colors do not appear are of the typical form, with a prox- 

 imal flattened region, a longer attenuated portion, and well- 

 developed barbicels on the distal barbules. They present their 

 dorsal margins upward in a dorsal view. There is a compara- 

 tively sparse pigmentation with the typical rod-shaped granules of 

 melanin found in feathers. 



In the region of metallic colors, one finds the proximal bar- 

 bules essentially like the distal barbules and flattened throughout 

 their extent. The attenuated portions characteristic of typical 



