380 Lieut. -Col. R. Meinertzhagen on [Ibis, 



By applying existing theories to migration in general, 

 it was found that they were usually only applicable to a 

 particular species at one particular spot, and it became 

 apparent that until a fairly comprehensive grasp could be 

 got of the migration of each species throughout its range, we 

 should not progress to any great degree. 



The rules governing the migration of a species in Great 

 Britain need not necessarily apply to that same species 

 when passing from its summer quarters in other parts of the 

 world to, say, India or Egypt. Each species contains many 

 communities, and even very small local colonies, whose 

 summer and winter homes and routes of migration are 

 governed by laws which are almost individualistic. Not 

 only each species and subspecies, but every small colony or 

 family of birds presents on occasions a separate problem, 

 the solution of which may differ in accordance with the 

 many varied laws governing the migratory habit. In this, 

 connection it is interesting to quote Whitlock (' Migration 

 of Birds/ final paragraph) : — 



" Every species, nay, every little clan of birds has its 

 own migratory history, resembling as a whole the 

 story of the common flight, but on the other hand 

 differing in many points in its minor details.^' 



Before, then, the migration of any species can be studied 

 as a whole, a detailed knowledge of its Geographical 

 Distribution Avill be necessary, and in grappling with this 

 question we are at once confronted with the question of 

 Subspecies or Geographical Bepresentatives. 



A Subspecies is an incipient species and is evolved ab 

 initio from exactly the same causes as a species. The causes 

 of variation in species or subspecies may be roughly sum- 

 marized as follows : — We may attribute variation in size to 

 the quantity or quality of food, variation in structure to 

 some essential habit developed in the daily search for food 

 (it is hoped to show at some future date that length of wing 

 is not dependent on length of migration, but on daily habit), 

 special decorative development to courtships necessitating 



