CONTENTS. xi 



mudas — Its Abnormal Character — Migration over Seas 

 by means of Islands — Migration over the Mediter- 

 ranean- — The North Sea Routes — Rarity of Migration 

 to New Zealand — -Migration Routes Continuous— Ant- 

 arctic Migration — Geological Changes in Antarctic 

 Regions — Coast Routes of Migration — Their Conti- 

 nuity — -How followed by Migrants — Ancient Routes 

 of Migration — Instances of Species still following 

 them — Subnierged Land Areas — Coast Migrants — 

 Valley Routes of Migration — Cross Valley Routes — 

 Valley Routes to India — Abnormal Migrants to that 

 Country — American River Routes — River Valleys 

 exceptionally favourable to Migrants — Mountain 

 Routes of Migration — Mountain Migrants — Migra- 

 tion through Mountain Passes — Varied Character of 

 Migration Routes — Routes of Migration indicating 

 Emigration ... ... ... ... ... ... 88 



CHAPTER V, 



EMIGRATION AND EVOLUTION. 



Confusion between Emigration and Migration — Defini- 

 tion of Terms — Theories of Avian Distribution — 

 Primary Causes of Emigration — Local Causes of 

 Emigration — Irruptic Emigration — Irruptions of Sand 

 Grouse — Irruptions of Pastors, Jays, and Goldcrests — 

 Chronic Emigration — Birds extending their Range — 

 Present Lines of Migration an Indication of Past 

 Routes of Emigration — Ancient Routes of Emigra- 

 tion — Emigration of Ouzels and Snipes — Recent 

 Avian Emigration in the British Islands — Emigrations 

 of House Sparrow — Emigration resulting in Migra- 

 tion — Emigration and Evolution — North Polar Emigra- 

 tion caused by Glacial Epoch — Island Species of 

 Birds — Islands and Routes of Migration — Influence 

 on Insular Avifaunas — Avifauna of the Galapagos 



