92 ANIMAL LIFE AND SOCIAL GROWTH 



owls and hawks find their food more plentiful 

 and they too increase in numbers. Then just 

 as the point of greatest abundance is reached 

 comes the "crash" in the cycle. The lemmings 

 and the mice die off and disappear as if by magic 

 leaving an increased population of predatory 

 foxes, hawks, and owls to shift as best they can 

 in the face of a diminishing food supply. They 

 too migrate. The snowy owl comes down into 

 New England and New York by the thousands 

 at such times and causes great loss of life among 

 the native small birds and rodents. These 

 predatory migrants usually perish in their turn, 

 for in the case of the owls at least, the evidence is 

 that they do not return north and they cannot 

 successfully breed in the southern regions which 

 they penetrate. 



It is well known that there is a sun spot cycle 

 of about 11 years. This affects the temperature 

 of the earth's surface, which is higher when there 

 are fewer sun spots. Atmospheric pressures and 

 rainfall of different parts of the earth also vary 

 with the sun spots. The tracks of the regular 

 cyclonic storms in North America shift with more 

 or less regularity and this shift appears to be 

 correlated with the sun spot cycle. The changes 

 in level of Lake Victoria in Africa show a high 

 correlation with the sun spot cycle. 



