6 British Diving Ducks 
mid-May to mid-July (Saxby). Incubation is by the female alone, and it seems she does 
not leave the nest at all once she has commenced to sit (W. H. St. Quintin, Avic. Mag., 
1899, p. 115; Saxby, B. of Shetlands, p. 249 ; Blaauw, &c.). The period of incubation lasts 
from 27-31 days. (W. Evans, Ibis, 1891, p. 73, 27-28 days; C Life, March 21, 1908, 
p. 409, and British Birds, ii. p. 65. F. G. Paynter, 31 days; Saxby, B. of Shet lands, 4 
weeks ; F. E. Blaauw, 28 days ; Tiedemann, 28 days.) For details of the down (which 
varies considerably in colour) I must refer my readers to Mr. H. Noble's paper in British 
Birds (vol. ii. p. 39, pi. II., fig. 13, 13). 
Many accounts have appeared in the works of naturalists on the subject of the plumage 
of the male and female Eider {Somateria m. mollissima) and the age at which the sexes 
arrive at maturity. In nearly all of these there is much guesswork owing to the small 
series of specimens examined, although in several of the accounts it is stated correctly that 
the male bird becomes adult in its third year. 
So long ago as 1756 we find the description of the typical (Swedish) Eider by M. Thrane 
Briinnich, who, roughly, yet accurately, states that it is not until the third year that the 
male "in all things resembles the adult male," and "they do not pair until the third year 
unless through an irregularity or an occasional wantonness." With his description of the 
plumages of the immature female I cannot agree, for he states that ''during the first year 
the female bird alone attains almost the same plumage as the mother bird, the only difference 
being that they are somewhat lighter," &c. Later in his Supplement III. he states that the 
two white bands on the wings do not become distinct until after several years' moulting. 
This is somewhat contradictory. Various authors such as Nilsson, Lilljeborg, M. von 
Wright, all give descriptions of various stages of the plumage, but in no way seem to come to 
definite conclusions. Faber (Prodroimis der Isldndischen Ornith., p. 70, 1822) says that the 
male bird is not capable of procreation until its fifth summer, and that it retains its youthful 
plumage four years. Kjaerbolling (Skandinaviens Fugle, p. 691) thinks that in the first and 
second year the male bird lacks the beautiful markings on the head, and the white is entirely 
absent on the neck or begins on the throat. Brehm, too {Handbuch der Naturgeschichte alle 
Vog. Deutsch^j, is equally inaccurate in his statements about the age when the male gets its 
full plumage. After Briinnich, Holboll [Oritith. Beitrag zttr Fauna Gronlands, pp. 69-73) 
seems to have been the next author who diagnosed the plumage-change of the Eider 
correctly. On page 72 he says that, having compared a great number of young birds of 
both species {S. mollissima and S. spectabilis), he has come to the conclusion that both 
require two years to become full grown, so that young birds which were hatched in 1840 
were full grown in the autumn of 1842, and had attained a complete winter-plumage in 
October.^ This period, he states, is alike for both sexes. During the first year the female 
bird is quite grey, without the white bands on the wings ; in the second year she attains 
almost the same colour as the old birds, only differing from these by the absence of the 
white bands on the wings. Professor Collett gives {Minor Conwmnications Avifatina 
Norway, 1 881-1892, pp. 284-6) a detailed account of the plumage-change which seems to 
leave the reader in a state of some doubt, for he believes that the young males do not begin 
to turn white until the second winter. Most English authors, except Booth, say very little 
^ Broadly speaking this is quite correct, although many males do not attain full plumage until December, owing to the delay 
in moulting. 
