110 



Note on the Soaring of the Ha^wk. 



By T. W. Kirk, F.R.M.S., cl^c, of the Geological Survey 

 Dei^artment of New Zealand. 



[Read December 3rd, 1889.] 



The peculiar notched or cut-away shape of the primary feathers 

 in the wings of many birds, more especially of the " Raptores," 

 or " Birds of Prey," has often attracted my attention, and the 

 purpose of such emargination has been a source of curiosity to 

 me for many years. 



It will be observed that the outer portion of both the anterior 

 and posterior vanes of the primary feathers of the wing (I am 

 speaking of the feather as though it were in position in the ex- 

 panded wing) are cut away — the former for about half its length, 

 the latter for rather less. The form of these feathers has, of 

 course, been frequently described, but I have never seen any 

 explanation of why their shape should be as it is j indeed, I 

 believe no such explanation has been published. I recently 

 stumbled, so to speak, upon a discovery of what may possibly 

 lead to a solution of the question. 



When up country a short time ago I saw a large Hawk (Circus 

 Gouldi) shot while soaring. After receiving the charge it con- 

 tinued to soar, although rapidly descending, and fell at some dis- 

 tance with both wings extended. On going to pick it up I was 

 surprised to observe that, though quite dead, its wings were still 

 expanded, and that the primaries were locked, or kept extended, 

 by a partial reversal of their vanes — the terminal half of the 

 posterior vane of each feather overlapping the corresponding 

 portion of the front vane of the feather immediately behind it. 



The question arose. Was this j)osition of the feathers due to 

 accident, or had the bird the power of placing them in this 

 apparently unusual relationship ? and if the latter, with what 

 object 1 



After a careful examination I replaced the vanes in what, until 

 more information is obtained, must be regarded as their correct 

 position. I then extended the wing, and after a few experiments 

 found that by manipulating the joint with the fingers, so as to 

 give a slight rotary motion, just before full expansion was at- 

 tained, the primaries could be made to take the position they 

 occupied when first examined — that is, the locked position. This 

 seems to prove that the bird had the power of, at will, altering 

 the relative position of these feathers. If such a supposition can 

 be placed beyond doubt, it will give a decided indication of the 



