>58 



NATURE'S CALENDAR 



December 6 



strange and beautiful aberrations known 

 to collectors have no doubt been produced 

 by the action of frost which has occurred 

 at the season when the larv^a was pupating. 

 The species believed by the writer to be 

 most prolific in aberrations are species 

 which pupate early in the spring from 

 caterpillars which have hibernated or 

 which pupate late in the autumn. Some 

 are species found at considerable altitudes 

 above sea-level, where late frosts and early 

 frosts are apt to occur." 



The semi-annual change of plumage in 

 birds, and of pelage in mammals, is an 

 adaptation to the alternating periods of 

 heat and cold that make up the year. 

 The winter plumage of our northern birds, 

 such as may be seen in a mid-December 

 ramble, is denser and more closely inter- 

 locked than that which follows the spring 

 molt, and it is almost always duller in hue, 

 too, and hence lessconspicuous. The ducks 

 and related birds have a downy under- 

 growth, which not only serves the main 

 purpose of preventing water reaching the 

 breast, but also serves to resist cold. It 

 is this underwear of down, which loosens 

 in the spring and is gradually dispensed 

 with, that is plucked out and utilized by 

 the female ducks as bedding for their 

 eggs. The down obtained from the nests 

 of the eider-duck, and justly regarded as 

 a luxury by us for its lightness and 

 warmth, is the special undercoat assumed 

 by that arctic fowl for winter, which, 



December 7 



