90 



THE WOODPECKERS 



shows the shape of the curve in six species, and 

 indicates that, while the cur- 

 vature is less than we might 

 expect, it bears some relation 

 to the bird's way of living ; 

 for we see that the strictly 

 arboreal woodpeckers have 

 more pointed tails than the 

 terrestrial species, and that 

 the amount of gradation 

 bears a direct relation to the 

 amount of time spent upon 

 the tree-trunks. 



There is a third difference, 



Diagram of curvature of the shape of the individual 



feather, to which we shall re- 

 fer again ; but now we wish to 

 examine the uses and mean- 

 ing of the curved end. 



I will show you how to 

 prove this point so that you 

 may be satisfied about it even 

 if you should never see a 

 woodpecker. We will make 

 a little experiment, so simple 



that even a child can understand it. 



First, how many shapes can any bird's tail 



have ? It may be one of three general patterns, 



tails of Woodpeckers. 

 Drawn to scale. 



a, a, point of insertion in 

 rump. 



a, b, outer tail feather. 



a, c, middle tail feather. 



If the outer tail feather 

 were of the same length in 

 all cases, the curve at the end 

 of the tail would be repre- 

 sented by the dotted lines. 



1. Flicker. 



2. Ked-headed Woodpecker. 



3. Downy Woodpecker. 



4. Logcock. 



5. Central American Ivory- 

 billed Woodpecker. 



6. North American Ivory- 

 billed Woodpecker. 



