12 



ANIMAL LIFE IN DESERTS 



is found only in desert areas or that it is an invariable 

 characteristic of the desert climate. It occurs very 

 generally in the more pronounced deserts, and the 

 following are striking examples : 



It might be supposed that the number of rainy days 

 per month or per year would be closely correlated 

 to the monthly or annual precipitation, but this is 

 not the case, for very great variation occurs in the 

 amount of rain which falls on the average rainy 

 day. In some desert climates it falls in minute 

 amounts, and the number of rainy days may therefore 

 be relatively large. This is characteristic of the 

 South AustraHan Desert. At Oodnadatta, for in- 

 stance, one-third or even one-half of the annual 

 precipitation (4-68 inches : 118 mm.) is in amounts 

 of less than 0-15 inch (4 mm.) : such minute 

 amounts of water do not moisten the soil to an 

 appreciable depth, and are very quickly evaporated. 



