'Spring migration is scarcely completed before there occur 

 certain summer movements which precede the true autumn 

 migration." A. Landsborough Thomson, Bird Migration 



10 



The Classification of Waterfowl Travel 



Our word "migrate" comes from the Latin migratus, 

 the past participle of migrare : "to move from one place to another." It lacks 

 the element of permanent settlement carried in the word "emigrate" and is 

 defined by Webster's Dictionary as "to pass or remove from one region or 

 district to another for temporary residence." 



Most of us think of migration as the spring and autumn sweep of birds 

 to and from their nesting ranges. Many authors, however, have used the 

 word with reference to other travel occurring between the two main pas- 

 sages. The literature is thus sometimes confusing; ornithologists seem not 

 to have found in "migration" so precise a meaning as it still holds for lay- 

 men. There have been many attempts to correct this situation, like Geyr 

 von Schweppenburg's suggestion (1933) that we adopt the term Zwischen- 

 zug, or "between-migration," to distinguish all travel taking place between 

 spring and fall. I prefer the more recent idea of Wilkinson (1952). He pro- 

 poses that we refer to the vernal and autumnal migrations to and from the 

 breeding grounds as anastrophic migration — from the Greek avaarpefoiv, "to 

 retrace one's steps." All other movement he catalogues as diasporic migra- 

 tion — from the Greek Siao-Tropa, "dispersion." 



The travels of waterfowl come neatly within these two broad classifica- 

 tions, and placing the various migrations in one or the other category does 

 much to strengthen our understanding. 



ANASTROPHIC MIGRATION 

 Homeward spring migration 



Homeward spring migration carries the bird from the place where its 

 sexual drives are awakened to the nesting region where the reproductive 



135 



