20 MICHIGAN BIRD LIFE. 



would have to be considered, for there are at least eighteen other ]\lichigan 

 birds, belonging to twelve different families, which have more or less blue 

 in their plumage, and several of them (Kingfisher, Blue Heron, Tufted Tit) 

 are also conspicuously crested. Moreover, questions of color are often 

 very difficult ones, the average individual being unable to discriminate shades 

 nicely, or at least to name them accurately. Color, therefore, has been kept 

 out of the artificial keys so far as practicable, and the aim has been to select 

 characters for consideration which are clear, definite and readily recognized, 

 so that the student can tell at a glance whether the specimen before him 

 possesses that character or not. 



Technical terms will be found defined in the glossary near the end of the 

 volume, and most of the important structures used in classification are 

 illustrated by text figures, a list of which follows the table of contents at the 

 beginning of the book. 



MIGRATION. 



The Century Dictionary defines migration as follows: "The act of mi- 

 grating; change of residence or habitat; removal or transit from one locality 

 or latitude to another, especially at a distance." In further explanation 

 the same authority adds, "Migration seems to be determined, primarily 

 and chiefly, by conditions of food supply, but this does not fully account 

 for the apparently needless extent and the wonderful periodicity of the 

 movement, nor for the fact that individuals sometimes return to exactly the 

 same spot to breed again after passing the winter perhaps thousands of miles 

 away." 



The term migration as applied to birds is familiar to every one, and the fact 

 that many of our birds desert us each autumn and return in the spring is so 

 familiar that even the most unobservant can scarcely have failed to note it. 

 The more careful student will have seen, however, that not all our birds 

 leave us in fall, and possibly he may have guessed also that those which 

 return in the spring are but a fraction of those which withdrew the previous 

 year. In all the life-histories in the present w^ork reference will be found 

 to the character of residence, and in those species which migrate regularly 

 an attempt is made to give approximately the dates of arrival and departure. 

 It must be remembered, however, that Michigan covers a long distance from 

 north to south (more than 400 miles) and that dates will vary much with 

 latitude and other conditions. It seems wise therefore to devote a few pages 

 here to a consideration of the facts of bird migration in general as well as in 

 our own state. 



Considering merely the condition of residence we may divide our birds 

 into four groups: First, residents or permanent residents, those which 

 are with us all the year. Second, summer residents, or summer visitors, 

 those which nest with us. Third, transients, or birds of passage. Fourth, 

 winter visitors or winter residents.* 



Not a few of our common birds are residents in one part of the state and 

 only summer visitors or even transients in anothci', Avhile other species come 

 regularly or occasionally into the northern parts of the state in the winter 

 but never reach the southern counties. The Snow Bird or Junco and the 

 White-throated Sparrow are transients in the southern half of the state, 

 but summer residents in the northern half; while the Meadowlark and Mourn- 



* Much of what follows on tliis subject is taken verbatim from the autlior's paper entitled "Fact 

 and Fancy in 15ird Migration." Eighth Rep. Mich. Acad. Science, 1906 (1907), pp. 13-25. 



