INTRODUCTION. 



A bird is a feathered vertebrate animal; or, to describe it more 

 fully, it is an air-breathing, warm-blooded, feathered, oviparous (egg- 

 laying), vertebrate animal, having a four-chambered heart, and a 

 complete double circulation. Birds occupy a place in nature inter- 

 mediate between the mammals and the reptiles, and many naturalists 

 consider a bird to be merely a modified reptile. 



These feathered vertebrates are recognized by zoologists as be- 

 longing to a Class named Aves to distinguish them from other animals, 

 and the Class is separated into subclasses, which in turn are again 

 subdivided into orders, suborders, families, subfamilies, genera and 

 subgenera and finally into species and subspecies. 



Birds belonging to the same family, but which show decided and 

 constant differences, are recognized as species, whereas if the differ- 

 ences in color or size are not very great and intermediate forms occur 

 showing an intergradation from one to the other, they are called races 

 or subspecies. Races or subspecies are really species in process of 

 development, and are caused by difference in climate, food, etc. 



It should be borne in mind, however, that the line of demarkation 

 between a species and a subspecies is a purely arbitrary one, and is 

 largely a matter of individual opinion. Subspecies are distinguished 

 by a third name; for example, Dendroica palmar-urn hypochrysea 

 is a race or subspecies of Dendroica palmarum. 



Having learned something as to what a bird is, let us take up in 

 order the more important external parts, such as the wing, tail, bill, 

 and feet. 



THE WING. 



As an aid to identification, the wing characters are most impor- 

 tant. The terms primaries, secondaries, axillars, wing coverts, etc., 

 are constantly used in describing birds, and the student should learn 

 to recognize them at a glance. 



13 



