100 , Diseases of Northern Birds. 



same of the Iceland falcon, in his Account of Iceland, p. 148, 

 and many of the natives have maintained the truth of the fact. 

 The white-bellied parasitic Lestris, is not an older variety of the 

 brown-beUied, but both these colours are found even in the nest. 

 The same is the case with the white magpie, and the white cor- 

 morant of the Faroe Isles; and certainly so with the Rotche 

 (Uria alle)^ Tyste (Cephus grylle)^ and Anas Jiistrionica, in 

 Greenland. But although the tint of colour does not alter with 

 age, the lustre of the feathers diminishes in the males, and the 

 appendages of the feathers when they occur elongate. The older 

 the heron, the longer is his beard. It is the same with the lap- 

 wing, with the collar in the Podiceps and Charadrius, and with 

 the long tail feathers of the Arctic gull (Lestris parasitica)^ 

 Anas glacialls and acuta. It is, therefore, very uncertain to 

 estimate the age of birds by the length of these parts. When 

 the female as well as the male is provided with these ornaments, 

 they also lengthen with age. There is, however, one appearance 

 in the female indicative of an advanced age. When the sexes are 

 of different colours, as in some gallinaceous birds, when they cease 

 to lay eggs, assuming the splendid plumage of the male, as the 

 young male at first resembles the female. I have also seen old 

 females of the Mergus merganser and serrator^ Anas glacialis, 

 histrionica, and crecca, with somewhat of the plumage of the 

 male. 



Disease does not seem to characterise the old age of birds. 

 In the wild state,, they are seldom affected by sickness, and cer- 

 tainly by no regular debility. Only whilst moulting, they are 

 sluggish, depressed, and conceal themselves ; but this change is, 

 in the wild state, seldom mortal. There is no doubt that the 

 young eider-duck is often preyed upon by a growth in the ab- 

 domen, about the size of a goose's egg ; and the Uria troile 

 and Brunnichii are often in winter exhausted by some unknown 

 weakness, and found dead on the sea-shore. In certain years, 

 the Sula alba seems to be subject to a contagious disease, and 

 then is thrown up in great numbers on the coast of Iceland. 

 Otherwise the northern birds are only subject to disease, except 

 such as are brought on by accidental causes, as when their legs 

 are frost-bitten, or frozen to the ice, as often happens with the 

 Alca tarda, Uria troile, Brunnichii and alle ; or when their 



