GLACIAL EPOC LIS AND POLAR CLIMATES. 6i 



looking upon the movement north to higher and 

 cooler latitudes each spring as an undertaking never 

 to be missed. Warmer and warmer became the 

 southern haunts, stimulating and widening migration 

 flight to the cooler temperatures prevailing near the 

 edges of the retreating glaciers, where a suitable 

 breeding climate could only be found. 



Let us confine our attention solely to the birds 

 that bred in the British Islands. In the Pras- 

 Glacial ages this area formed part of Continental 

 Europe ; a rich and fertile corner, abounding in 

 insect life, full of haunts the Flycatcher loved. 

 After the banishment of its race and the exile of its 

 ancestors in Africa, the northern journey at first 

 did not extend further than the edges of the glaciers 

 on the Mediterranean coasts of Europe. But as 

 these disappeared, and a warmer climate began to 

 prevail in higher latitudes, the annual summer flight 

 was increased. Every century the northern breed- 

 ing range had increased ; creeping slowly across 

 France ; higher and higher with the growing 

 vegetation ; nearer and nearer to the haunts of old. 

 During the slow gradual elevation and submergence 

 that isolated Albion from the rest of Europe during 

 Post-Glacial time, the regular spring journey across 

 the sea became wider and wider ; but with the 

 intense and inherited love of home in their tiny 

 breasts, the individuals that were born and bred 

 in this district never failed to return each yean 

 For 60,000 years or more has this species now 

 crossed the sea, returning every season, not only to 

 our islands, but each pair of individuals as long as 



