584 



THE COMMUNITY 



lemmings. Bird life is remarkable for its 

 vast abundance in the brief summer, when 

 the waterfowl of the world seem to be 

 gathered to the treeless tundra for the nest- 



permanent, as in the polar bear and snowy 

 owl, or seasonal, as in the arctic fox and 

 hare, and in the ptarmigan. Insect hfe in- 

 cludes a surprising number of Diptera. 



Fig. 218. Tundra landscape: Muskoxen in arctic North America. The muskox was circum- 

 polar in the tundra biome until recent time. (From habitat group in the Chicago Natural His- 

 tory Museum. ) 



Fig. 219. Polar landscape in Antarctica: emperor penguins, the largest and southernmost 

 species of penguin. ( From habitat group in Chicago Natural History Museum. ) 



ing season. Summer wealth is followed by 

 extreme impoverishment in winter, when 

 even the snowy owl may be driven into the 

 adjacent zones. White coloration may be 



There are notably large bumblebees, in 

 which the body temperature is maintained 

 by the by-product of heat from their vibrat- 

 ing wings, and conserved by their insulating 



