BIRDS AS CONSERVATORS OF THE FOREST. 



239 



and cents is difficult of determination, but careful study has brought out much of 

 practical importance by ascertaining approximately to what degree each species 

 is harmful or helpful in its relation to the forests. Their subsistence is obtained 

 for the most part upon trees, a mode of life for which they are specially adapted. 

 The character of the feet and tail enables them to cling easily to upright trunks, 

 and the structure of the bill and tongue gives them the power to cut into solid 

 wood and withdraw the insects lodged within. The toes are in pairs, one pair 

 projecting forward and the other backward, and are furnished with very strong, 

 sharp claws, an arrangement which insures a firm hold upon the bark. The tail is 



Fig. 1 — Tongues of woodpeckers : 

 a, hyoid of flicker (Co/aptes auratits); 

 by tip of tongue of downy wood- 

 pecker {Dryobates ptibescens). 



Fig. 2. — Special development of tongues of woodpeckers : a, skull 

 of flicker (Colapies aitratus). showing root of tongue extending to 

 tip of bill (after Lindahl); />, head of hairy woodpecker (Dryobates 

 vilZosus), showing root of tongue curving around eye (after Audu- 

 bon). 



composed of very strong feathers, each with a sharp, stiff point at the end, which 

 can be pressed against the tree trunk, and thus made to support and steady the 

 bird. The beak is rather long, but stout, with a chisel-shaped point which is 

 hardened and sharpened so as to render it a most effective wood-cutting instru- 

 ment. The tongue, which is the most peculiar portion of the anatomy of these 

 birds, is extended backward by two slender, flexible filaments of the hyoid bone, 

 each incased in a muscular sheath (Fig. 1, a). These filaments, instead of ending 

 at the back of the mouth, curve up over the back of the skull, across the top of the 

 head, and down on the forehead (Fig. 2, b), and in some species enter the opening 

 of the right nostril and extend forward to the end of the beak (Fig. 2, a). In the 

 last case the tongue is practically twice as long as the head. By means of its sur- 



