178 ECONOMIC ZOOLOGY 



covered with down and are able to run about or they are more or less 

 naked, blind and helpless; in the former case they are said to be pre- 

 cocious, in the latter case they are called non-precocious or altricial. 



Owing to their common occurrence about the haunts of man and 

 to their attractive appearance and songs birds have been more generally 

 studied than almost any other class of animals. Unfortunately, however, 

 owing again to the beauty of their plumage and to the delicious flavor 

 of their flesh, they have been hunted by man almost, or quite, in some 

 cases, to the point of extermination. Of recent years, fortunately, 

 partly through the efforts of the Audubon and other similar societies, 

 and through the work of the United States Biological Survey, 

 a widespread interest in the study and protection of birds has done 

 much to arouse public sentiment and cause the enactment of protective 

 laws, such as the McLean Federal Bird Law. This campaign of educa- 

 tion, to be noted later has already begun to bear fruit and the birds 

 in many localities are increasing in numbers in a very gratifying way. 



There are so many and such excellent bird books and illustrated 

 guides (see bibliography) on the market that only a few of the ways in 

 which birds are of economic importance to man will be here noted. For 

 the same reason space will not be given to the discussion of poultry 

 and other common domestic birds, since that is a science in itself and 

 is represented by a large library of literature. 



The classification of the birds is so complicated and unsettled that 

 little will be said of it here. Practically every text-book uses a different 

 method from the rest, but most authors divide the class, which is es- 

 timated to contain 10,000 to 12,000 species, into two sub-classes: i. 

 Archaeornithes and 2. Neornithes. The former contains the single 

 species Arch&opteryx lithographica, Fig. 112, the interesting Upper 

 Jurassic form that possess the teeth, claws, long tail, etc., of the 

 reptiles but the feathers characteristic of birds. It is an excellent ex- 

 ample of a connecting type, showing the descent, that is also indicated 

 in other ways, of the birds from reptilian ancestry. 



The latter sub-class contains the living birds, and also a few extinct 

 forms which, while most interesting, have no economic bearing and 

 hence will not be discussed here. The Neornithes, in older texts, 

 are sometimes placed in two " Divisions" A. Ratitae and B. Carinatae, 

 and as a matter of convenience, these divisions will be used here. 



The Ratitae include several extinct forms, some of great size, and a 



