T. \Y. KiKK. — 0)1 tJic Soaiing uf the Hawk. 325 



the coast about forty miles north of Christchurch, which was 

 stocked witli rabbits some thirty years ago by Mr. Caverhill. 

 About every seven years disease nearly exterminates the 

 rabbits ; but the fittest survive and breed up again. The 

 reason is popularly supposed to be that the rabbits increase 

 beyond their food-supply, and, becoming weakened in conse- 

 quence, are attacked by disease. This Canadian disease may 

 be similar. E. Foster, Inspector, 



Christchurch. 



Art. XXXVI. — The Soaring of tlie Hawk — A possible 

 Reason for Notched Wing-feathers. 



By T. W. Kirk, F.E.M.S. 



[Read before the Wellington Philosophical Society, 31st July, 18S9.] 



Pl.\te XYIII. 



The peculiar notched or cut-away shape of the primary 

 feathers in the wings of many birds, more especially of the 

 Eaptores, or "birds of prey," has often attracted my atten- 

 tion, and the purpose of such emargination has been a source 

 of curiosity to me for many years. 



Before going further, however, allow me to direct your atten- 

 tion to this feather (Plate XVIII., fig. 1). You will observe that 

 the outer portion of both the anterior and posterior vanes (I 

 am speaking of the feather as though it were in position in 

 the expanded wing) is cut away, the anterior for about half its 

 length, the posterior 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 — indeed, I iDelieve no such explanation has been published. 



I recently stumbled, so to speak, upon what may perhaps 

 prove to be a solution of the question. When up country a 

 short time ago I saw a large hawk {Circus goiildi) shot 

 while soaring. After receiving the charge it continued to soar 

 although rapidly descending, and fell at some distance with 

 both wings extended. On going to pick it up I was surj)rised 

 to observe that, though quite dead, its wings were still ex- 

 panded, and the primaries were locked by a partial reversal of 

 their vanes, as shown in the specimen now on the table 

 (fig. 2). Fig. 3 shows the under-side of the same wing. 



The question arose, was this position 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 ? After a careful examination, I replaced the vanes in 



