OCR Text |
Show 1873.] MR. R. B. SHARPE ON FALCO ARCTICUS. 419 the markings on the chest are longitudinal drops (fig. 13) of a pale rufous-brown colour. The gradual dissolution and breaking up into three bars is shown in fig. 14. Hence, when the bars are perfectly developed, a shade of darker brown overspreads the upper margin, gradually eclipsing the rufous-brown shade, which remains the evidence of the previous plumage (fig. 15). Thence are shown two successive stages of the development of the dark brown shade which at last removes all traces of the reddish tint (figs. 16, 17). The last illustration which I shall have the pleasure of bringing before the notice of the Society is one of a species of American Kite, Cymindis uncinata, which undergoes excessive variation during the progress from youth to maturity. The young bird is white underneath, with a few irregular dusky cross bars (fig. 18). From this dress the next stage (fig. 20), which consists of bright rufous and buff bars, is gained by amoult (fig. 19), as will be seen by the feather just beginning to appear. The fading of the buff in the next stage leaves the under surface barred with white and rufous in very distinct contrast (fig. 20). Hence the rufous bars gradually change into blue (fig. 22); and that this is gradually effected will be seen by the feather figured, which still retains traces of its former rufous colour (fig. 21) now dying away. The last plumage of the bird is apparently entirely blue underneath, as the gradual extension of the blue cross bars, which merge together by degrees, would entirely cover the entire under surface (fig. 23). I have never seen any intermediate feather between fig. 21, which has only two cross bars, and fig. 22, which has three ; so that it is possible that a moult intervenes; in which case the change comes under rule 3. EXPLANATION OF PLATE XXXIX. Fig. 1. Dorsal feather of Falco candicans, very young. 2. Central tail-feather from same specimen. 3. Ditto, of slightly older bird. 4. T w o fresh-moulted dorsal feathers of a young Falco candicans, supposed to be in its first moult, x, the old feathers of previous plumage. 5. Dorsal feather of immature Falco candicans in full clean-moulted plumage, showing further advance towards cross bars. 6. Dorsal feather of immature bird, the supposed adult of " dark race." 7, 7 a. T w o dorsal feathers from mature bird, showing approach to longitudinal drop. 8. Tail-feather of same specimen. 9, 9a. T w o dorsal feathers of bird in "tear-dropped" plumage; the supposed young of " light race." 10, 10 a, 12, 12 a. Dorsal feathers from very old birds. 11. Tail of very old bird. 13-17. Breast-feathers of young Accipiter nisus, showing gradual change from drop to bars. 18. Breast-feather of very young Cymindis uncinata. 19. The same, showing fresh-moulted feather (19 a). 20, 21. Full plumage of C. uncinata. 22, 23. Breast-feathers of very old birds, showing gradual change from th? rufous to blue plumage. 27* |