[272] 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. [273] ‘History of British Birds,’ vol. i. 1839, p. 159. [274] Blyth, in Charlesworth’s ‘Mag. of Nat. Hist.’ vol. i. 1837, p. 362; and from information given to me by him. [275] Audubon, ‘Ornith. Biography,’ vol. i. p. 113. [276] Mr. C. A. Wright, in ‘Ibis,’ vol. vi. 1864, p. 65. Jerdon, ‘Birds of India,’ vol. i. p. 515. [277] The following additional cases may be mentioned: the young males of _Tanagra rubra_ can be distinguished from the young females (Audubon, ‘Ornith. Biography,’ vol. iv. p. 392), and so it is with the nestlings of a blue nuthatch, _Dendrophila frontalis_ of India (Jerdon, ‘Birds of India,’ vol. i. p. 389). Mr. Blyth also informs me that the sexes of the stonechat, _Saxicola rubicola_, are distinguishable at a very early age. [278] ‘Westminster Review,’ July, 1867, p. 5. [279] ‘Ibis,’ 1859, vol. i. p. 429, _et seq._ [280] No satisfactory explanation has ever been offered of the immense size, and still less of the bright colours, of the toucan’s beak. Mr. Bates (‘The Naturalist on the Amazons,’ vol. ii. 1863, p. 341) states that they use their beak for reaching fruit at the extreme tips of the branches; and likewise, as stated by other authors, for extracting eggs and young birds from the nests of other birds. But as Mr. Bates admits, the beak “can scarcely be considered a very perfectly-formed instrument for the end to which it is applied.” The great bulk of the beak, as shewn by its breadth, depth, as well as length, is not intelligible on the view, that it serves merely as an organ of prehension. [281] Ramphastos carinatus, Gould’s ‘Monograph of Ramphastidæ.’ [282] On Larus, Gavia, and Sterna, see Macgillivray, ‘Hist. Brit. Birds,’ vol. v. p. 515, 584, 626. On the Anser hyperboreus, Audubon, ‘Ornith. Biography,’ vol. iv. p. 562. On the Anastomus, Mr. Blyth, in ‘Ibis,’ 1867, p. 173. [283] It may be noticed that with vultures, which roam far and wide through the higher regions of the atmosphere, like marine birds over the ocean, three or four species are almost wholly or largely white, and many other species are black. This fact supports the conjecture that these conspicuous colours may aid the sexes in finding each other during the breeding-season. [284] ‘The Journal of Travel,’ edited by A. Murray, vol. i. 1868, p. 286. [285] See Jerdon on the genus Palæornis, ‘Birds of India,’ vol. i. p. 258-260.