6 THE IMPORTANCE OF BIRD LIFE 



several thousand more will be added. "^ In North 

 America there are about 1200 forms listed. Eu- 

 rope, Asia, Africa, and Australia are rich in. forms, 

 but a combined census — ^minus a thousand or two 

 island subspecies — shows them to contain alto- 

 gether scarcely more than the two continents of 

 the Western Hemisphere. 



Although fish lead in actual total number, birds 

 make not a bad second when compared with the 

 comparatively meager numerical strength of the 

 remaining vertebrates. We know that seventy 

 years ago hundreds of thousands of bison roamed 

 the plains of the West in herds so vast that they 

 extended beyond the horizon. Within the present 

 generation, even to-day, fifty and seventy thou- 

 sand caribou may constitute a single herd on the 

 frozen prairies of northern Canada and Alaska. 

 Audubon, however, in 1813, observed a flock of 

 passenger pigeons which took three days to fly 

 past a certain point! 



There were more than two and a quarter billion 

 pigeons in that one drove. * ' The air was literally 

 filled with Pigeons, the light of noonday was 

 obscured as by an eclipse. ..." Stefansson, 

 the arctic explorer, tells of Banks Island and 

 neighboring lands several hundred miles north 



1 Bacial forms as opposed to species are geographical sub- 

 divisions of the latter, generally diverging from the type in 

 color, size, or both. Thus, for example, there are described 

 twenty-two races, or subspecies, of the common song sparrow. 

 {Uelospiza, m. melodia), all found in North America. 



