OR THE YOUNG MAY HAVE AN INTERMEDIATE CHARACTER; OR, AGAIN, THEY MAY DIFFER GREATLY FROM THE ADULTS IN BOTH THEIR SEASONAL PLUMAGES.
The cases in this class are singularly complex; nor is this surprising, as they depend on inheritance, limited in a greater or less degree in three different ways, namely, by sex, age, and the season of the year. In some cases the individuals of the same species pass through at least five distinct states of plumage. With the species, in which the male differs from the female during the summer season alone, or, which is rarer, during both seasons (41. For illustrative cases, see vol. iv. of Macgillivray's 'History of British Birds;' on Tringa, etc., pp. 229, 271; on the Machetes, p. 172; on the Charadrius hiaticula, p. 118; on the Charadrius pluvialis, p. 94.), the young generally resemble the females,--as with the so-called goldfinch of North America, and apparently with the splendid Maluri of Australia. (42. For the goldfinch of N. America, Fringilla tristis, Linn., see Audubon, 'Ornithological Biography,' vol. i. p. 172. For the Maluri, Gould's 'Handbook of the Birds of Australia,' vol. i. p. 318.) With those species, the sexes of which are alike during both the summer and winter, the young may resemble the adults, firstly, in their winter dress; secondly, and this is of much rarer occurrence, in their summer dress; thirdly, they may be intermediate between these two states; and, fourthly, they may differ greatly from the adults at all seasons. We have an instance of the first of these four cases in one of the egrets of India (Buphus coromandus), in which the young and the adults of both sexes are white during the winter, the adults becoming golden-buff during the summer.
With the gaper (Anastomus oscitans) of India we have a similar case, but the colours are reversed: for the young and the adults of both sexes are grey and black during the winter, the adults becoming white during the summer. (43. I am indebted to Mr. Blyth for information as to the Buphus; see also Jerdon, 'Birds of India,' vol. iii. p. 749. On the Anastomus, see Blyth, in 'Ibis,' 1867, p. 173.) As an instance of the second case, the young of the razor-bill (Alca torda, Linn.), in an early state of plumage, are coloured like the adults during the summer; and the young of the white- crowned sparrow of North America (Fringilla leucophrys), as soon as fledged, have elegant white stripes on their heads, which are lost by the young and the old during the winter. (44. On the Alca, see Macgillivray, 'Hist. Brit. Birds,' vol. v. p. 347. On the Fringilla leucophrys, Audubon, ibid. vol. ii. p. 89. I shall have hereafter to refer to the young of certain herons and egrets being white.) With respect to the third case, namely, that of the young having an intermediate character between the summer and winter adult plumages, Yarrell (45. 'History of British Birds,' vol. i. 1839, p. 159.) insists that this occurs with many waders. Lastly, in regard to the young differing greatly from both sexes in their adult summer and winter plumages, this occurs with some herons and egrets of North America and India,--the young alone being white.
I will make only a few remarks on these complicated cases. When the young resemble the females in their summer dress, or the adults of both sexes in their winter dress, the cases differ from those given under Classes I. and III. only in the characters originally acquired by the males during the breeding-season, having been limited in their transmission to the corresponding season. When the adults have a distinct summer and winter plumage, and the young differ from both, the case is more difficult to understand. We may admit as probable that the young have retained an ancient state of plumage; we can account by sexual selection for the summer or nuptial plumage of the adults, but how are we to account for their distinct winter plumage? If we could admit that this plumage serves in all cases as a protection, its acquirement would be a simple affair; but there seems no good reason for this admission.