402 NATURE-STUDY REVIEW [16:9— Dec, 1920 



body, and in many birds the small bones are hollow, supplied with 

 air from the sacs. The lungs are not elastic, but are flattened 

 against the backbone and ribs. The temperature of the body is 

 regulated by the quantity of air exhaled with each breath. Feath- 

 ers, which are characteristics of birds alone, are planned entirely 

 for lightness and strength. Each feather is composite, consisting 

 of two rows of barbules on each barb and barbicels on the barbules. 

 The air cannot force its way through such a structure. Flight is 

 made possible by the acctmiulated resistance offered to the air. 

 Each feather is exactly fitted, in size, structure, shape and coloring, 

 for the part of the body in which it is found. These feathers are 

 renewed by the process of moulting. 



The extent to which the different senses are developed in the 

 bird is another interesting point. The nostrils of the bird are 

 encased in bone, with no exposed moist s^urface. As we would 

 expect, the sense of smell is relatively unimportant in the life of the 

 bird. Sight is most highly developed, in fact brought to such a 

 high degree of perfection that it is difficult for us, from the con- 

 sideration of our relatively poor eye sight, to comprehend it. 

 The eyes of any creature indicate the relative powers of its intelli- 

 gence, and the eyes of the bird are notably alert. There are three 

 functioning lids to the birds eye, and in nearly all birds the move- 

 ment of the lids is not the same as in hiiman beings. The way irt 

 which the eyes can adjust themselves from long to short focus in an 

 extremely short time is almost miraculous. Another well developed 

 sense is that of hearing. One very strong argument for the birds: 

 keen sense of hearing is, that birds would not be capable of such 

 wonderfully varied notes were their hearing not equally acute. 

 Taste is very poorly developed, but never entirely lacking, while 

 feeling is most active in the tip of the tongue and the beak. 



We now come to m.ore specialized characteristics of birds, as 

 regarded from the stand point of thejr feeding habits. Fish-eating 

 birds will be first considered. We find at once that adjustment 

 to feeding habits has produced m.arked results. Many of the 

 fish-eaters fly above the water, some near its surface, some further 

 up. The skimmers have a prolonged lower mandible by means of 

 which they can scoop up their prey from the surface of the water. 

 Other birds, like the terns and snake-birds, have sharp spear-like bills, 

 with which they are able to impale their prey. The pelican simply 

 swallows fish and water indiscriminately into its pouch, discards the 



