EVOLUTION OF THE COLORS OF BIRDS. 227 



animals (more especially man) in old age have their hair 

 turn gray or white, so species or genera, when on the 

 wane, may become albinistic. This might be considered 

 an exemplification of Hyatt's principle of geratology 

 (see ante, p. 78). If a species is in its prime, it would 

 tend to be superabundantly nourished — the adjustment 

 of the means of living being so perfect — and the surplus 

 of vitality would gradually expend itself in an increase 

 of pigment. If the pigment were a dark one, the more 

 closely the feathers were crowded with it, the blacker 

 the plumage would become. If a species, on the con- 

 trary, had passed its prime and were wearing out, it 

 would be imperfectly nourished, and less and less pig- 

 ment would be deposited until an albino form would re- 

 sult. Both the black and white coloration, as previously 

 suggested, might be of use as recognition marks, and 

 thus the assumption of such a plumage would be hastened 

 by natural selection. If, on the other hand, the black 

 or white, instead of being of use for recognition, was a 

 detriment to the species, by making it over-conspicuous, 

 the result would probably be the extinction of the race. 

 One of the few direct influences of food which have 

 been observed upon the colors of birds is the effect of 

 cayenne pepper. Dr. Sauermann has experimented 

 with a number of species, with some interesting results.* 

 These observations have been recorded by Beddard in 

 his Animal Coloration, together with other notes on the 

 effects of food upon color. Canaries have generally been 

 experimented upon,- the unfledged birds being fed with 

 food mixed with the pepper. Beddard reports Dr. 

 Sauermann's experiments as follows:! "Cayenne pepper, 

 of course, is a composite substance, from which a num- 

 ber of chemical substances can be extracted; the red 



* Archiv. Anatomie uud Physiol., 1889; Physiol., Abtheil., 543. 

 tl. c, p. 54. 



