Feathers 55 



are almost always due to pigment or colouring-matter in 

 the shaft or vane. If we take a black feather and hold 

 it to the light, it will still look black; if we pound it with 

 a hammer, it will not change. 



Green is never found as a pigment except in the 

 feathers of a small family of birds called plantain-eaters 

 or turacous, which inhabit West Africa. For some time 

 it was thought that the natives dyed the birds artificially, 

 as when these birds were kept captive, the magnificent 

 scarlet patch on the wing would gradually fade and 

 become a dull gray. It is a fact that this colouring- 

 matter washes out when the feather is washed in alkaline 

 water. Even ordinary water will be slightly tinged if the 

 feather is soaked in it. The pigment contains about ten 

 per cent of copper, and this can be extracted chemically 

 in the form of a metallic powder. The plumage of almost 

 all brightly coloured birds will fade in the course of years, 

 if the feathers are left exposed to direct sunlight; but, like 

 photographic plates, the hues of some birds are more sen- 

 sitive than others to the light. The delicate reds and 

 yellows on the lower parts of Mexican Trogons are par- 

 ticularly evanescent, and the rose-pink of the African 

 Fairy Warbler disappears a short time after death. 



We might speak of a third class of colours, which are 

 due to both pigment and structure. For instance, no 

 blue pigment is known to exist in the feathers of birds, 

 but blue feathers contain a brown or yellowish pigment 

 which is encased in the horny coating of the feather. 

 Between this outer sheath and the underlying pigment 

 is a layer of many-sided cones or small projections which 



