COLOUR IN BIRDS AND QUADRUPEDS. 209 



and middle states, clothed in a livery of white and black. The male 

 American Goldfinch (Fringilla tristis) is of a homely olive brown co- 

 lour during winter, whilst in summer it is a bright yellow. The Yel- 

 low Crowned Warbler is ash coloured during half of the year ; of a 

 beautiful blue in the other. Our Plovers, Tringas, Gulls, &c., are 

 subject to the same changes. Our ornithologists have widely dif- 

 fered in investigating this part of the physiology of birds. The sub- 

 ject of inquiry here seems to present itself under a new aspect, and the 

 inquiry is : 



3. Do birds which are subject to these semi-annual changes in plu- 

 mage receive their new colours in the spring, in consequence of afresh 

 moult, as they do in summer, or are they produced by a gradual fading 

 or brightening of the feathers, without a fresh moult ? 



Mr Ord, in a well vs^ritten article published in the third volume, 

 new series, of the Transactions of the American Philosophical Society, 

 has advanced the following theory. " It being now satisfactorily 

 proved that a change of colour obtains, in some birds, in the winter 

 and spring, without a change of plumage, I am disposed to conclude 

 that the state of moulting, properly so called, takes place in ail birds 

 but once a year." 



To this theory the following difficulties seem to present themselves. 

 The colour in the plumage of birds, especially in the small feathers, 

 most subject to a change, appears to be advanced to the extent it is in- 

 tended to arrive at, in a few weeks, or, at furthest, in a few months. 

 At that point it seems to become stationary, and to remain so for a 

 considerable length of time. If the same feathers are afterwards to 

 receive a fresh set of colours, there must be some secretions in the 

 body of the bird, and a fresh impulse given to the feathers already ad- 

 vanced to maturity, imparting to them properties which they did not 

 possess before. When it is necessary for a bird, in summer, to receive 

 a new dress, differing in colour from the old, there are no secretions 

 by which it can impart fresh colouring matter to its old feathers, which 

 have long become stationary in their growth and colour. It is, then, 

 essential that these feathers should be thrown off, and those substituted, 

 which, in the progress of their growth, and their advance to maturity, 

 may receive those hues destined for them by nature. This law of 



