Tails 407 



this, and by it the extremely quick dives and turns are 

 made possible. No feather would be stiff or rigid enough 

 to offer to the water the resistance which these feathered 

 seals require. 



Exceptions to the rudder use in flying birds are found 

 in the murres sea-birds which share the cliffs of our north- 

 ern coast with cormorants and gulls. The tail-feathers 

 of a murre are so short as to be useless for steering pur- 

 poses, so in flight the bird uses its webbed feet instead, 

 stretching them out behind, opening, turning, and twist- 

 ing them in harmony with the wings, with as satisfactory 

 results as could be desired. 



The shape of the tip of the tail varies greatly in birds. 

 It may be square or rounded, or cuneate, or indented 

 in the centre, or swallow-tailed, as we appropriately call 

 the latter deeply forked condition. These conditions may 

 be paralleled or duplicated in many different Families of 

 birds. For example, the forked type is seen in our com- 

 mon Barn Swallow, in those dainty relatives of the gulls, 

 the terns " Swallows of the Sea," and again in the 

 Forked-tailed Kite and the Scissor-tailed Flycatcher. 

 By closely watching a swallow as it courses swiftly over 

 a meadow, or shoots upward, buoying itself against the 

 breeze, we can appreciate the delicate adjustment of the 

 muscles which govern the tail-feathers. Each feather 

 seems vital with life, now sliding one over the other until 

 all are in a narrow line, then expanding, with less friction 

 than ever a fan opened, into a wide-spreading, gently 

 graduated fork. The quartet of forked-tailed birds men- 

 tioned above are splendid fliers, but we shall see that skill 



