18/3.] MR. K. B. SHARPS 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 evi- 

 dence 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 under- 

 neath, 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 a moult (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 con- 

 trast (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. Two 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 plu- 



mage, showing further advance towards cross bars. 



6. Dorsal feather of immature bird, the supposed adult of " dark race." 



7. 7 a. Two dorsal feathers from mature bird, showing approach to longi- 



tudinal drop. 



8. Tail-feather of same specimen. 



9. 9a. Two dorsal feathers of bird in " tear-dropped " plumage; the sup- 



posed 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 the 

 rufous to blue plumage. 



27* 



