4 THE MIGRATION OF BIRDS. 



migration still remained but little understood, and 

 it may be safely asserted that only within the past 

 twenty years or so has any real light been thrown 

 upon the subject. 



Probably no other portion of the economy of 

 birds has been surrounded with so much mystery 

 as that which embraces their periodical journeys 

 to and fro. The various migratory birds were 

 wont to disappear at stated seasons, and to re- 

 appear at others. Such movements w^ere too 

 palpable to be denied. The Cuckoo appeared 

 in spring, and just as surely vanished from the 

 woods and fields in early autumn ; so likewise did 

 the Swallows and the Swifts, and the various 

 small birds that swarm in our islands with each 

 recurring summer. Before the geographical dis- 

 tribution of birds had advanced to the dignity 

 of a science, before the uttermost parts of the 

 earth were scrutinized by competent observers, 

 and the avifaunas of wide tracts of country became 

 known through the mdomitable pluck and per- 

 severance of collectors, the destinations of these 

 birds of passage were very imperfectly known ; 

 and little surprise can be felt that men sought to 

 explain the disappearance of these birds in another 

 way. In other words the Cuckoo, the Swift, and 

 the various species of Swallows were said not to 

 leave this country at all, but actually to spend their 

 winters with us, either, as in the case of the Cuckoo 

 by becoming transformed into a Hawk, or, as in 

 the case of the Swifts and Swallows by sinking into 



