THE TRAVELS OF BIRDS 



to rear the young; and when this task is finished 

 the birds leave the nesting ground. 



"But," you may ask, "if the Brown Pelican 

 goes only as far north as Pelican Island, why 

 does his cousin, the White Pelican, go all the 

 way to Great Slave Lake in British America?" 

 You might ask the same question about many 

 other bird travelers that winter in the South 

 and nest in the Far North. 



We have every reason to believe that when 

 last the Arctic regions were warm, White Peli- 

 cans fished along the borders of the Arctic Ocean. 

 When the climate began to change and became 

 cooler and cooler, they, of course, had to retreat 

 slowly southward. Finally, we know that the 

 great ice sheet reached as far south as the central 

 part of the United States. At that time the 

 White Pelican must have lived on the Gulf of 

 Mexico and probably farther south. 



Then as the climate began to grow warm 

 again, the ice slowly melted ; each year the great 

 sheet grew smaller until at last the land was free 

 as it is today. As the ice disappeared, the White 



