BIRDS— YOUNG LIKE BOTH ADULTS. 475 



own. — In this class the sexes when adult resemble each other, and 

 differ from the young. This occurs with many birds of many 

 kinds. The male robin can hardly be distinguished from the 

 female, but the young are widely different, with their mottled 

 dusky-olive and brown plumage. The male and female of the 

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

 the scarlet color, 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 color often occurs with brilliant 

 males when they are confined. With many species of herons 

 the young differ greatly from the adults; and the summer plu- 

 mage of the latter, though common to both sexes, clearly has a 

 nuptial character. Young swans are slate-colored, 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 colored, 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 colors 

 have been acquired through sexual selection by the nearly ma- 

 ture 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 ma- 

 ture resemble each other and differ from the young. 



Class IV. When 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 colored, resemble each other. 

 Such cases are, I think, more common than those in the last class. 

 We have in England instances in the kingfisher, some wood- 

 peckers, the jay, magpie, crow, and many small dull-colored 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 colored 

 than the adults, but many of the feathers on the lower surface 

 are edged with brown,-' — 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 



" Jerdon, 'Birds of India,' vol. i. pp. 222, 228. Gould's 'Handbook to 

 the Birds of Australia,' vol. i. pp. 124, 130. 



