418 MR. R. B. SHARPE ON FALCO ARCTICUS. [Apr. 1, 



irregular shape of fig. 9 indicates that it is not perfect, and that it will 

 undergo a further change ; and although the marking is not of the 

 same form as the feather placed in juxtaposition, they both have the 

 same object in view, and are neither of them so very unlike fig. 10. 

 The heart-shaped spot is, as far as we at present know, the limit 

 beyond which adult Greenland Falcons "can no further go." 



To return to the question of the light and dark races, I would ask 

 the advocates of that view of the question to which they would refer 

 a specimen with the dorsal feathers as illustrated in figs. 7 and 7 a. 

 The right-hand figure belongs to the young of the " light " race, but 

 the left-hand one should be referred to the "dark" race. It is to 

 me self-evident that fig. 7 is the previous stage of such a feather as 

 fig. 9 a ; and it is equally clear that fig. 7 a is the antecedent stage 

 of fig. 7. The tail (fig. 8) is also closely allied to fig. 11, but still 

 shows traces of the markings visible on all birds of the " dark race," 

 which have here not entirely dissolved ; thus the tail, as well as the 

 dorsal featherings, is intermediate between the two races, and to my 

 mind illustrates their connexion. The sequence from the triply 

 barred stage (fig. 6) to the longitudinal drop is not so clear, unless 

 these changes are more rapid than we have at present supposed, or 

 that the feather regains its longitudinal form by the gradual closing 

 up and re-joining of the bars, which, from the irregular outline on 

 the middle bar of fig. 6, seems not absolutely impossible. It appears 

 likely, however, that a partial moult may intervene between the 

 stages indicated in fig. 6 and figs. 7 and 7 a ; for I have noticed in 

 some Accipitrine birds changes which induce me to believe in a rule 

 which may be enunciated thus : — 



Rule 3. That in the progress to maturity, when the changes of 

 plumage are very different from one another, the new dress still 

 retains an indication of what the former one was like before the 

 moult. 



Thus, if fig. 7 a is the result of a moult, it still shows evidences of 

 the previous barred plumage, though they quickly disappear (fig. 7) 

 and pass through the stages (figs. 9, 9 a, 10) to the final spots (figs. 

 10 a, 12, 12 a), which, from their irregular outline, might seem 

 intent upon getting even smaller still. 



Let any one who doubts the possibility of markings such as those 

 on the Greenland Falcon becoming gradually changed without an 

 intermediate moult, study the changes exhibited by the common 

 Sparrow-Hawk in its progress towards maturity. The general cha- 

 racteristic of the species of Aecipiter is to have a striped plumage 

 when young and a barred dress when old. But it is not generally 

 known that this is effected by a gradual change in the mark- 

 ings of the feather, and not by an actual moult. Just as in the 

 Greenland Jer Falcon we could tell the age of a bird by the state 

 of the bars on the tail, so we can tell that of a young Sparrow-Hawk 

 by the extent of the rufous edging to the feathers of the upper sur- 

 face : if these are very broad and distinct, the bird is quite young ; 

 for they gradually wear off as it progresses in age. On the first 

 appearance of the feathers from the downy covering of the nestling, 



