CONTEXTS xv 



PAGE 



Earliest to Arrive — Growing Intensity of the Movement — 

 The Hardier Species are Latest to Appear — Autumn Migra- 

 tion of Fieldfare and Redwing — The Earliest Departures 

 from the British Area — Early Migrants Abnormal — The 

 Growing Intensity of Southern Migration as Autumn ad- 

 vances — Duration of Migration Periods — The Migration 

 into the British Area from the East — General Aspects of 

 the Phenomenon — Abnormal Lines of Migration in Autumn 

 — Cross Migration in Autumn — Reversal of Route by 

 Migratory Birds — Erroneous Interpretation of the Facts — 

 The True Explanation— Duration of Autumn Migration- 

 Vertical Migration in Autumn — Order of Migration — Table 

 indicating the Autumn Migration of Birds across the 

 British Islands ... ... ... ... ... ... ... 260' 



CHAPTER XI. 



INTERNAL MIGRATIONS AND LOCAL MOVEMENTS IN THE 

 BRITISH ARCHIPELAGO. 



Meagreness of Data bearing on this Question — Local Move- 

 ments in Spring and Summer — Internal Migration always 

 takes place within Normal Areas of Dispersal — Birds do 

 not wander from their Areas — Comparative Movements of 

 the Snow Bunting, the Northern Bullfinch, and the Crested 

 Titmouse — Emigration only undertaken during the Season 

 of Reproduction — Local Movement amenable to Law — 

 Eftects of Severe Winters on Birds — Results of such Move- 

 ments ineffectual in extending Area — Redwings and Severe 

 Weather — The Want of Carefully-kept Records — Local 

 Movements at Lighthouses — Irruptic Movements — ^Their 

 Futility as Colonizing Agents ... ... ... ... ... 276. 



CHAPTER XII. 



SUMMARY .\ND CONCLUSION. 



The Present Volume illustrates the Development and Appli- 

 cation of a New Law of Dispersal — Past Geographical and 

 Climatic Changes — The Glacial Epoch and its Bearing on 

 the New Law of Dispersal — Effects of the Glacial Epoch 

 on Species — Range Bases — Application of the Law of Dis- 

 persal to the Range Contraction and Emigration of British 

 Birds — The Migration of British Birds — Routes of Migra- 



