BIRDS OF NEW YORK STATE 



159 



Osprey Nu Os8 



This bird is alighting on its nest and the tail is spread to check 

 the momentum. 



Marsh hawk Nu HM8 



Compare with the preceding. 



2 The uses of the wings 



There are live different types of flying for which there are as 

 many types of wings, the different birds being best adapted for 

 one particular method of flying. 



a Ordinary flight 



This is accomplished by a rhythmic up and down motion of 

 the wings held at such an angle that the resultant of the forces 

 drives the bird forward. The best type of wing for ordinary 

 flight is one of average proportions such as already seen in the 

 bluebird (Nu Bm8) and night heron (Nu HeBS). 



b Sailing 



Accomplished by holding the wings outstretched at such an 

 angle that, without any motion, the resultant of the forces of 

 wind and gravity drives the bird ahead. Birds that depend upon 

 this method of locomotion often remain on the wing for long 

 periods. The best type of wing is a long narrow one, carried to 

 the extreme in the albatrosses but illustrated in many North 

 American birds. 



Caspian terns Nu TfC6 



These birds are sailing over their nesting island. Note the 

 length of wing as compared with the length of body and the 

 width of wing. The wings of all the birds are in nearly the same 

 positions, indicating that they must be holding them in a uniform 

 position. 



Sooty tern Nu TfS7 



Note the position of the wings. These birds can balance 

 themselves on the wind for hours at a time without any apparent 

 motion of their wings. 



Common tern Nu TfD 



Note the great length of the wing. 



