XVI. 21 



BEAKS 



467 



fruit. Incidentally we may notice the ingenious behaviour by which 

 the snail's shell is cracked open to obtain the food, by beating it against 

 a stone. Birds that mainly eat seeds, such as the finches, usually have 

 short, thick, strong bills. Large strong bills are present in the hornbills 

 and toucans ; they push through dense foliage to obtain the fruit, which 

 may have a hard case. In parrots the beak is moved on the skull, 

 pushed up by the upper jaw when the latter is pulled forward by the 

 digastric muscle. 



Fig. 280. The Galapagos woodpecker finch (Camarhynchus pallidus) using 

 its stick. (From Lack, drawn by R. Green from photograph by R. Leacock.) 



The carnivorous birds, such as most eagles and owls, have short 

 and sharp beaks, whereas fish-eating, as in other vertebrates, results 

 in long jaws. Another widely found arrangement is the flattened bill 

 of some ducks, similar to those of some sturgeons and of the platypus, 

 which also sift out food from water or mud. The long, thin beak of the 

 curlew selects food from mud in a different way, mostly worms and 

 other soft-bodied invertebrates. Lesser flamingos feed on blue-green 

 algae and microscopic phytoplankton, collected by a filter system on 

 the jaws, using a current of water produced by the sucking mouth and 

 piston-like tongue. Some insectivorous birds have long beaks for 

 finding their prey under bark. The woodpeckers have a strong beak 

 like a pick-axe for excavating in wood, and most elaborate special 

 modifications for the purpose of licking up insects; there is an enor- 

 mously long protusible tongue and special hyoid. The woodpecker 

 finch {Camarhynchus pallidus) on the Galapagos Islands probes insects 

 from the bark by means of a cactus spine, a remarkable case of the use 

 of a tool by a bird (Fig. 280). Among the most specialized feeders are 



