UNBALANCE IN NATURE 89 



six inches long when fully grown, but about half 

 this length is tail. The arctic tundra in Lap- 

 land, Greenland, North America and Siberia is 

 fairly alive with these animals. In many places 

 the moss-covered ground is riddled with lemming 

 holes and the lemmings are among the most joy- 

 ous features of the tundra. With the activity of 

 rabbits they pop in and out of their holes keeping 

 the while a sharp outlook for their arch-enemy, 

 the snowy owl. They are key -industry animals 

 of the tundra and are at the base of the food pyra- 

 mid not only for the snowy owl but also for arctic 

 wolves and arctic foxes; and even the polar bear 

 when ashore, hunts and feeds on these tiny 

 lemmings. 



Lemmings do not remain at a steady level of 

 population year after year; quite the opposite. 

 Their periodic increases in abundance have been 

 so conspicuous that they have been known to 

 many men for centuries. As a result of such 

 increases they become too numerous to obtain 

 food in their native habitat and accordingly act 

 as do many other animals, man included, when 

 faced with threatened starvation; they migrate. 



Lyell, friend of Charles Darwin, recorded such 

 migrations approximately as follows: Once or 

 twice in a quarter of a century 1 they appear in 



1 More recent studies show that "lemming years" come every 

 third or fourth autumn. 



