94 THE BIOLOGY OF BIRDS 



catches small fishes in its laterally compressed " coulter- 

 like " bill, and is able to add one after another till it has 

 perhaps five, the tongue being probably used to hold the 

 captives firm when the beak is opened to add others. 

 Extreme specialisation is seen in the Skimmer (Rhyncops), 

 a sort of tropical tern, where the bill is long, high, and as 

 thin as a paper-knife. The bird flies very close to the 

 surface and skims the water with the mandible which is 

 longer than the upper jaw. When the knife-edge of the 

 mandible touches a little fish or a shrimp it projects the 

 booty into the open mouth. The skimmer is also said to 

 skim the soft mud. The very opposite extreme is seen in 

 the broad bills of ducks and geese, which are used in sifting 

 small animals out of the mud. The sifting is facilitated by 

 horny fringes on the bill and also on the tongue. In the 

 Shoveller Duck the arched bill has comb-like epidermic 

 processes at the edges which form an eflFective sieve for 

 keeping the food in while the water drains out. In the 

 related long-legged Flamingo the lower jaw is much arched 

 and the whole beak is bent down on itself, almost at right 

 angles, so that it is thrust upside down into the mud from 

 which it sifts out small molluscs and the like. 



Another line of evolution is illustrated by the long 

 slender bills of some of the humming-birds which are well 

 suited for probing to the nectar hidden deeply in the flowers, 

 and also in some cases for extracting a small insect from a 

 crevice. The opposite extreme is seen in the broad, widely 

 gaping, short bill of the swifts and the goatsuckers, very 

 well suited for capturing insects in mid-air. Similarly, we 

 may contrast the slender bills of wrens and warblers, suited 

 for deaHng with small insects, and the thick conical beaks 

 of finches suited for opening dry fruits and cracking dry 

 seeds. 



From a few we may learn all, and it is not necessary to 

 go further in illustrating the adaptations of bills. Three 

 points, however, should be noted. 



(i) The adaptations often show a remarkable nicety, 

 which indicates the specialised mode of feeding in many 



