CHAPTER XIII. 



THE MIGRATION OF INLAND BIRDS. 



As understood by me, the migration of a bird is sim- 

 ply the desertion of a given locality for a certain and al- 

 ways the same portion of each year. As an example, the 

 common house-wren is migratory, in that it remains in 

 New Jersey only from late in April until late in Septem- 

 ber, having left its southern home for six months. 



Before endeavoring to determine the causes of this 

 movement on the part of some birds, we must first note 

 the various features characterizing the movement itself 

 for it may safely be asserted that no two birds migrate 

 in the same manner, although the similarity is marked 

 among the various species of the same family. The most 

 notable feature in migration is the apparent uniformity in 

 the time of its occurrence ; that is, of the dates of the ar- 

 rivals in spring and of the departures in autumn. Is 

 this arrival in spring as regular as claimed by some and 

 supposed by most people ? To the casual observer, and 

 indeed to many who have for years noted the first appear- 

 ances of our various birds, the arrival seems to be quite 

 regular ; and, curiously enough, we find many such ob- 

 servers insisting that, however late a bird may be, any one 

 season, he is never earlier than a given date. Thus we 

 have been frequently told that the wrens are never seen 

 before May 1st, and that usually upon that day they 

 are here in full force. Now, let any one watch day and 

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