HuTTON. — On the Flight of the Black-hacked Gull. 143 



Pettigrew to tlie extraordinary opinion that the forward movement of a bird 

 is derived from a stroke delivered downward and forward. 



Dr. Pettigrew, and many other authors, hold the opinion that the wing 

 feathers of a bird open and close during the up and down strokes respectively. 

 But however this may be with birds that only flap their wings slowly, it is, I 

 think, almost impossible that such rapid changes should take place in the 

 wings of a bird like the sparrow, which, according to Professor Marey, makes 

 thirty-three vibrations per second. Dr. Pettigrew's experiments, also, upon 

 the sparrow, with alternate feathers taken out of the wing, show that an 

 opening and shutting movement is not necessary for flight ; and we may safely 

 assume on the jjrinciple of greatest economy of force, a principle always acted 

 upon throughout nature, that what is not necessary is not used. 



The falconers of olden days were well aware that rapidity of flight depended 

 on the primary feathers of the wing, a.nd they called these the " flight 

 feathers," while the secondaries they called the " sail feathers," and it will be 

 found that the swiftness of a bird's flight depends on the length of the 

 primaries in proportion to the size of the bird, and on the number of strokes 

 it makes per second. Thus the swift, which has proportionately longer 

 primary feathers than any other bird, is probably the fastest flier, while the 

 partridge, which has broad wings but short primaries, flies heavily, and has to 

 make very rapid strokes. The wild-duck has less area of wing in proportion 

 to its weight than a partridge, but its primaries are longer, and consequently 

 it flies much faster. The landrail also is another example of a slow-flying 

 bird with considerable expanse of wing for its weight, but with short pri- 

 maries. The heron also furnishes another instance of the same kind, and it is 

 well known that the long winged falcons are far superior fliers to the round 

 winged buzzards, vultures, and eagles, although in the latter the area of wing 

 surface is probably greater than in the former. 



The way in which birds turn in the air has also been much misunderstood. 

 Professor Owen {Comp. Anat. of Vert. 11. , 115) advances the extraordinary 

 theory that when a bird wishes to turn it beats the air more rapidly with one 

 pinion than with the other, which liowever originated with Borelli in his 

 " De Motu Animaliur}i.^^ 



Van der Hoven {Handbook of Zoology, II., 371) also reiterates the same 

 opinion, while Macgillivray {I.e. I., p. 420) says that turns are efiected by the 

 contraction of one wing and the extension of the other, aided by the tail. 



The real method of turning, however, is very simple, and was, I believe, 

 first pointed out by me in the Ibis for July, 1865, p. 297. It must be remem- 

 bered that when a bird is flying the reaction of its wings against the air is 

 not only forward but also upward, the latter being necessary to counteract the 

 force of gravity. If now a bird lowers its right side, so that the axis from 



