ADAPTATIONS OF BIRDS 261 



bones and give great strength in movement. The rate of move- 

 ment of the wing differs greatly in different birds. The wing of a 

 bird is slightly concave on the lower surface when outstretched. 

 Thus on the downward stroke of the wing more resistance is 

 offered to the air. The soaring of birds is probably accomplished 

 by very slight movements of the wings which result in making 

 use of wind currents. 



The tail is sometimes used in balancing; its chief function, 

 however, appears to be that of a rudder during flight. Most birds 

 have under the skin of the tail a large oil gland, whence comes the 

 supply of oil that is used in waterproofing the feathers when they 

 preen themselves. 



■ Crown. 



-forehead 



.upper mandible 



neck— — „,._ J- ^J" ^1 



back— £ +******* -■■/' *~- lower mandible 



^ o./-' / H- throat 



rump. 



* ^ J>"'£^ibAr--/ —coverts 



tail coverts,^/- \ A^^^a^^x/ ^.^...........treast 



^yKfyJlL .- ahdamexi. 



l ^^0L - flanks 



^ ..toes 

 hind toe. 



Find and list all the adaptations in this bird. Explain the value of each adaptation named. 



Thinly feathered and featherless areas can be found on the body 

 of any bird, although these areas. are so well covered by the over- 

 lapping feathers that no bare places are to be seen. There are 

 i several kinds of feathers on the body of a bird. Soft down feathers 

 | make a warm body covering ; larger feathers, known as contour 



H. BIO — 18 



