UNITED STATES 
DEPARTMENT OF THE INTERIOR 
Bureau of Biological Survey 
Office of Regional Director 
404 U.S. Courthouse 
Portland, Oregon 
January 4, 1940 
Chief, Bureau of Biological Survey, 
U. S. Department of the Interior, 
Washington, D. C. 
Attention: Mr. Day. 
Dear Sir: 
Reference is made to letter of December 22nd from Mr. Day. 
I wish to offer the following information relative to our obser- 
vations in Idaho and neighboring states with respect to the sub- 
ject of rodent and grouse cycles. 
Our experience with ground squirrels and jack rabbits bears 
out your observations in Wyoming public land area heavily in- 
fested with ground squirrels and black-tailed jack rabbits. We 
have planned our control operations on the basis of three success- 
ive years intensive treatments to effect practical control. Having 
reached that point we have reduced control operations to a minimum 
consisting of policing or treating focal points of infestation to 
further reduce populations, or at least prevent reinfestation or 
distribution of resident populations. 
There has been unmistakable evidence of disease in ground 
squirrels throughout Southern Idaho during the past 30 years. The 
first widespread and noticeable epidemic was reported as occurring 
in 1910 or 1911. The next general epidemic occurred on a wide- 
spread basis in 1921 and 1922. The third sporadic epidemic in 
some localized areas occurred from 1935 to 1938 on a more or less 
intermittent and localized basis. 
Die-off or plague, or whatever might have been the cause of 
epidemics, was confined very largely to areas where rodent popula- 
tions, particularly ground squirrels and jack rabbits, were com- 
paratively numerous and where they had not been materially reduced 
in numbers as a result of control operations.