140 Transactions. 



Art. ^Yl. — On the Flight of the Black-hached Gull (Larus dominicanus). 

 • By Captain F. W. Hutton, C.M.Z.S. 



[Read before the Aucldand Institute, I'dth August, 1872.] 



The phenomenon of flight has of late years attracted considerable attention, 

 and the subjecb has been very fully and ably discussed, especially by Dr. 

 Pettigrew, of London {Trans. Lin. Soc, 1868, p. 197), and Professor Marey, 

 of Paris {Smithsonian Report, 1869, p. 226). Both these authors have been 

 very successful in explaining the flight of insects, but considerable obscurity 

 seems still to exist as to the actual movements of the wings of birds when 

 flying. Mr. Macgillivray {British Birds, Vol. I., p. 31) said that the effective 

 stroke of the Mdng is delivered downward and backward, and suggested that 

 during the down stroke the resistance of the air bends upward the free tips of 

 the feathers, and the reaction thus produced gives a forward impulse to the 

 bird. The Duke of Argyll {Reign of Law, p. 132, 1867) and Professor 

 Marey both hold a similar view, but while the former maintains that the 

 effective stroke is delivered directly downward, the latter says that his 

 experiments prove that during the down stroke the wing moves first slightly 

 forward, then more and more backward ; and in the up stroke at first 

 backward, and then forward into its original position again. Dr. Pettigrew 

 on the other hand asserts that the effective stroke is delivered downward and 

 forward, and that by a peculiar twisting or screwing motion of the wings, 

 which I confess I do not quite understand, the air is forced to escape near the 

 root of the pinion, between the secondary and tertiary feathers, in a downward 

 and backward direction, thus by its reaction supporting the bird and driving 

 it forward. 



Professor Marey again says that during the greater part of the down stroke 

 the wing, by turning on its axis, slopes forward and downward, while during 

 the up stroke it slopes forward and upward, thus being on this jDoint quite 

 opposed to Dr. Pettigrew, who states distinctly that during the down stroke 

 no depression of the anterior margin and elevation of the posterior one takes 

 place. Dr. Pettigrew, and the Duke of Argyll also, both say that during 

 flight the point of the wing describes a " wave track," or simple undulating 

 line through the air, while Professor Marey says that his experiments show 

 conclusively that it describes a more or less regular cycloidal curve, or looped 

 line. All four authors, however, agree that the wing is extended during the 

 down stroke, and more or less folded during the up stroke. Under these 

 circumstances a few observations that I have made on the movements of the 

 wings of the common black-backed sea-gull during flight may prove of interest, 

 for not only do they point to a theoiy of progression much simpler than any 



