Chap. XVI. Birds — Young like both Adults. 481 



scarlet ibis are alike, whilst the young are brown ; and the 

 scarlet-colour, though common to both sexes, is apparently a 

 sexual character, for it is not well developed in either sex under 

 confinement ; and a loss of colour often occurs with brilliant 

 males when they are confined. With many species of herons 

 the young differ greatly from the adults; and the summer 

 plumage of the latter, though common to both sexes, clearly 

 oas a nuptial character. Young swans are slate-coloured, 

 whilst the mature birds are pure white ; but it would be 

 superfluous to give additional instances. These differences 

 between the young and the old apparently depend, as in the last 

 two classes, on the young having retained a former or ancient 

 state of plumage, whilst the old of both sexes have acquired a new 

 one. When the adults are bright coloured, we may conclude 

 from the remarks just made in relation to the scarlet ibis and to 

 many herons, and from the analogy of the species in the first class, 

 that such colours have been acquired through sexual selection by 

 the nearly mature males ; but that, differently from what occurs 

 in the first two classes, the transmission, though limited to the 

 same age, has not been limited to the same sex. Consequently, the 

 sexes when mature resemble each other and differ from the young. 

 CLASS IY. IV hen the adult male resembles the adult female, the 

 young of both sexes in their first plumage resemble the adults. — In this 

 class the young and the adults of both sexes, whether brilliantly 

 or obscurely coloured, resemble each other. Such cases are, J 

 think, more common than those in the last class. We have in 

 England instances in the kingfisher, some woodpeckers, the jay, 

 magpie, crow, and many small dull-coloured birds, such as the 

 hedge-warbler or kitty-wren. But the similarity in plumage 

 between the young and the old is never complete, and graduates 

 away into dissimilarity. Thus the young of some members of 

 the kingfisher family are not only less vividly coloured than the 

 adults, but many of the feathers on the lower surface are edged 

 with brown, 27 — a vestige probably of a former state of the 

 plumage. Frequently in the same group of birds, even within 

 the same genus, for instance in an Australian genus of parro- 

 keets (Platycercus), the young of some species closely resemble, 

 whilst the young of other species differ considerably, from their 

 parents of both sexes, which are alike. 28 Both sexes and the 

 young of the common jay are closely similar ; but in the Canada 

 jay (Perisoreus canadensis) the young differ so much from their 

 parents that they were formerly described as distinct species. 29 



27 Jerdon, ' Birds of India,' vol. i. 28 Gould, Ibid. vol. ii. pp. 37, 40, 



pp. 222, 228. Gould's ' Handbook to 56. 



the Birds of Australia,' vol. i. pp. 29 Audubon, ' Ornith. Biography, 



124, 130. vol. ii. p. , r >o. 



