falconidjE. .59 



effect of age, and it seems extraordinary that a structure so apparently essential 

 should not be developed at the time nature intends the bird should seek its own 

 sustenance. It has, indeed, been observed that the bill of the Falco Islandicus is 

 sometimes destitute of a notch ; and although we have attempted to account 

 for this variation, still it is by no means certain that this may not indicate a 

 difference of species. That there is some ground for this supposition, it may 

 be as well to mention that, although the difference between C. cyaneus and cine- 

 raceus may be very well drawn from the structure of the wings, yet that a more 

 important distinction between them has been overlooked. In cyaneus, the festoon 

 of the upper mandible is fully developed, and distinctly apparent, during every age 

 of the bird, whether male or female ; while in C. cineraceus this festoon is abso- 

 lutely wanting in every specimen we have examined, in all of which the commissure 

 of the bill perfectly resembles that of the bird before us (No. 8). Nevertheless, 

 from the following differences in the structure of their respective wings, we do not 

 feel justified in considering them as of the same species : — 



Falco cineraceus, a perfect adult bird, in the Bird No. 8, above mentioned. 



Paris Museum (Busard Montagu) . 



First quill feather, equal to the sixth ; First, intermediate between the sixth and 



seventh ; 



Second, in the least degree longer than the Second, half an inch shorter than the fifth ; 



fourth ; 



Third, the longest ; Third and fourth, equal and longest ; 



Fifth, intermediate in length between the first Fifth, a very little longer than the second. 



and second. 



To illustrate further the variation in the wings of the young and adult birds of 

 this group, the following measurements were taken from a male bird of the first year 

 (avant la premiere mue), belonging to C. cineraceus, and now in the Paris Museum. 

 First quill feather intermediate between the sixth and seventh ; second equal to 

 the fifth ; third shorter than the fourth, which is the longest. The colours of this 

 specimen assimilate very closely to our bird (No. 8), and tend to show that the 

 latter is a bird of the first year. Like ours, it is almost entirely of a bright rufous 

 beneath, without any other indications of those stripes, which are afterwards appa- 

 rent, than a dark line down the shaft of each feather. 



Adult specimens of cineraceus, brought from India by M. Sonnerat, exhibit the 

 following variations : Male. First quill much shorter than the sixth, but inter- 

 mediate between the sixth and seventh ; second rather shorter than the fourth ; 

 third the longest ; fourth longer than the second. Female. First quill feather 



i 2 



