USE OF THE KEYS. 35 



are brought into the same subsections, and the more variable species 

 may be placed in several widely separated sections. 



The maker of keys, however, should not try to serve two masters. 

 If the keys will identify, they will have accomplished their purpose. 

 The classification of our birds is shown in the body of the book, where 

 the species are arranged according to the system adopted by the Ameri- 

 can Ornithologists' Union. 



In making these keys the birds are first assorted into several major 

 sections or groups, according to the markings of some one part of the 

 body. Each one of these sections is preceded by the same kind of 

 number or letter. The heading of a group or section applies to all the 

 species included in it. Thus, if I does not apply to the bird you are 

 identifying, you must pass at once to II, or III, or IV, as the case may 

 be. In like manner, if the bird does not fall into sections 1, A, or a, 

 we go to 2, B, or b, respectively. Even should the first section describe 

 your bird, it is well to read the sections which are contrasted with it. 



As a model to show how the keys are used, let us identify, first, a 

 male adult Red-winged Blackbird — a black bird with a red and buff 

 shoulder-patch. Turning to the key to the family Ideridce, or Black- 

 birds, Orioles, etc., we read : 



" I. With yellow or orange in the under parts. 



" II. Under parts black, with or without metallic reflections. 



" III. Under parts grayish, slate color, chestnut, or buffy. 



" IV. Under parts black and white, or black tipped and margined 

 with rusty." 



Our bird has the under parts entirely black, so it evidently belongs 

 in Section II. Under this section we read : " A. Outer tail-feather 0*75 

 or more shorter than middle ones; bill 1*00 or more in length." Our 

 bird has all the tail-feathers of nearly equal length, the bill less than 

 an inch long. It can not therefore belong in A, so we go to B and 

 read : " Outer tail-feather little if any shorter than middle ones ; bill 

 less than 1*00 in length." There is no other section, and we con- 

 clude that our bird belongs here. Now we find a, b, c, d, each one 

 placed directly beneath the other, and each one leading to the name 

 of a species. This means that the statement following these letters 

 refers to some mark or character by which one of these species may be 

 known from the other, and that we should read them all. First comes 

 " a. Entire plumage bluish black." That will not do. Second, " b. A 

 red and buff shoulder-patch." Evidently this refers to our bird, but 

 we confirm our belief by glancing at c and d, neither of which can 

 apply to our specimen ; we decide, therefore, that it is a Red-winged 

 Blackbird, and turning to the extended description of Agelaius phoB- 

 7iiceus verify our identification. 



