Professor Aldo Leopold. 
 
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November 10, 1939 
 
not of this magnitude. I have often felt that this important 
general biological principle was not taken into account by 
rodent control officers as fully as it should be. I have 
felt that this was the case, especially here, in California, 
where conditions in the Canadian Zone at one end of 4&  coun- 
tty were cited as illustrative of what was to be expected for 
a related species of rodents which occurred in the Lower Sonoran 
Zone at the other end of the countfy. Comparisons and conclu- 
sions made on any such basis as that are almost certain to be 
wrong. 
I trust you will pardon this exposition on my part 
of a biological principle which I feel all too frequently has been 
over-looked by the agents,up to now concerning themselves with 
the regulation of the number of wild animals in general and 
rodents in particular. 
Very truly yours, 
ERH: hg                                4