COLOURS OF THE FEATHERS OF BIRDS. 23 



But besides this, the whole plumage of many birds becomes of a 

 brighter hue at the approach of the breeding season ; a fact which is 

 exemplified in a remarkable degree in the forehead and breast of a 

 cock linnet, which, in the winter season, appear of a dingy dark red, 

 but, at the season for pairing, become of a fine bright scarlet. The 

 beautiful roseate tinge, also, which distinguishes the breast of a cock 

 whitethroat in the summer, is no longer observable after the bird has 

 moulted, but seems to be entirely acquired at the commencment of the 

 breeding season. 



Hence, it is reasonable to infer with Mr. Selby, " that an invisible 

 circulating fluid pervades every feather, and consequently the plumage 

 may be considered so far an actual part of the living bird, as to be under 

 the influence of such constitutional change as the bird may at any time 

 experience. 



" That such circulation takes place is moreover evident, from the 

 striking difference which he observed in the elasticity *, between 

 the feather upon a bird whilst alive, and upon the same bird a short 

 time after death. In water-birds, this principle of life in the feather 

 (if I may be allowed the expression,) is singularly apparent ; as the 

 plumage that is impervious to water upon the living bird, is almost 

 immediately after death subject to its effect. 



" There can be no reason, then, why the feather may not be influ- 

 enced by the constitutional state of the bird, and as that is in the 

 highest degree of vigour immediately previous to the season of propa- 

 gation, why may not such vigour be exhibited to the very extreme 

 points of the circulating medium, by a partial variation of colour, or 

 an increased lustre of tone in the former hue of the feathers ? 



" It is not fanciful, for it has been established as a maxim in patho- 

 logy, that the state of health in man may be ascertained by the occa- 

 sional flaccidity or crispness of the hair ; and have we not repeatedly 

 met with well authenticated instances of great and sudden changes 

 having taken place in its colour, acting only, of course, through the 

 organic structure of the body. 



" Changes of colour in the hair of many quadrupeds are seen, and 

 that also at particular seasons ; and (as Dr. Fleming asserts, in the 

 case of the stoat, and some others, that assume a winter's garb,) with- 

 out any actual shedding of their coat, either upon their first variation, 

 or in regaining their summer's hue." 



* Mr. Selby also mentions " brilliancy of colour," fyc., but I have never observed this 

 in any remarkable degree. 



