INTRODUCTION. 15 



Scattered through the following pages will be found numerous so-called 

 keys for the separation of suborders, famiUes, and species, and a Httle exami- 

 nation of these will show that the plan upon which they are constructed is 

 based upon the presence or absence of certain characters or sets of characters, 

 so that the student with specimen in hand simply needs to determine first 

 which one of two statements fits the specimen in hand, his decision in this 

 case leading to the comparison of two other statements, and so, step by step, 

 he is led to recognize in his specimen the existence of certain definite peculiari- 

 ties and eventually reaches a conclusion applicable only to a single order, 

 family or species, as the case may be, and that the one represented by the 

 bird in hand. Having thus located the order, suborder or family to which 

 his specimen belongs he turns to the section describing the members of that 

 group and there finds another key which in the same way will lead to a 

 smaller group and this in turn to the species. Probably the beginner will 

 be struck at once by the fact that some characters which he has supposed 

 quite important are rarely selected, while others which may seem trivial 

 are very largely used. Thus, for example, color or color pattern is used much 

 less frequently than size or the proportions of various parts. This naturally 

 leads to a discussion of the facts which make it possible to arrange these 

 artificial keys. 



At the outset it should be made clear that all the individual birds belong- 

 ing to the same species are essentially alike in size, proportions and color, 

 after suitable allowance has been made for sex, age and season. A bird is 

 said to be adult when it is old enough to breed, and in most cases this point 

 is reached after a single year's growth. But such a breeding bird is not 

 necessarily mature in the scientific sense, as shown by the fact that its plumage 

 may change repeatedly and for several years before its color pattern and the 

 colors themselves become permanent. This is seen clearly in the Bald Eagle, 

 which does not get the pure white head and tail until at least three years of 

 age, sometimes doubtless not before the fourth year, though yearling birds 

 are believed to nest as a rule. Essentially the same thing is true of many 

 other birds of prey, as well as of many water birds. These cases nevertheless 

 are exceptional and most of our smaller birds become practically mature 

 in a single year, though it seems certain that they may improve somewhat 

 in appearance for several successive years. This is noticeable in such birds 

 as tanagers, grosbeaks, bluebirds, and others in which the males are brightly 

 colored. There is much variation in the perfection and brilliancy of plumage 

 among these males, some retaining considerable areas of the dress charac- 

 teristic of immaturity, while others, apparently the most robust and vigorous, 

 exhibit the characteristic plumage in the highest degree of perfection. Possi- 

 bly, or even probably, these variations are not entirely due to difference in 

 age, yet it seems fairly certain that this is the most universal factor. As 

 regards size, however, there is little or no change after the first year (except 

 in a very few cases), and as a rule young birds old enough to fly and care for 

 themselves are as large as their parents. For example, young robins or 

 bluejays two weeks after leaving the nest have practically the same measure- 

 ments (however, not the same weight) as their parents. Every observant 

 person, however, knows perfectly well that the young robin of this age is still 

 heavily spotted on breast and back, in this respect entirely unlike its parents, 

 while the young bluejay of the same age resembles its parents much more 

 closely, the differences lying not so much in color or pattern, as in the lax 

 and fluffy texture of the plumage, the decidedly shorter crest, and a certain 

 dullness and lack of brilliance about the colors themselves. 



