UNIVERSITY OF CALIFORNIA 
MUSEUM OF VERTEBRATE ZOOLOGY 
BERKELEY, CALIFORNIA                                         November 10,1939

Professor Aldo Leopold, 
Division of Wildlife Management, 
College of Agriculture, 
Madison, Wisconsin. 
Dear Professor Leopold: 
Your letter of November 3, to Linsdale comes when 
he is away in the Middlewest. According to the itinerary 
he left with us he will be at Route 1, Baldwin, Kansas, un- 
til November 11 and will go to Madison, Wisconsin, November 
14.                                H tte will arrive at Madison 
on November 14. He is going there primarily to see you. I 
am sending on your letter to him at Baldwin by air mail in 
the hopes of catching him. 
I have not the counts made of squirrels and other 
vertebrates on the Pt. Lobos Reserve since the publication 
by Grinnell and Linsdale of their report. I understand from 
Linsdale that there has been a decrease in the number of squir- 
rels, as the native vegetation has started to reestablish it- 
self on the Reserve. 
May I offer my own personal wordtQnmendation for 
your having injected into the rodent control problem this ques- 
tion of environment control. Of course, those who wish to main- 
tain something approaching a natural balance of organisms, what- 
ever that may be, might not wish to see the rodents reduced be- 
yond a certain level. Someone who wished to harvest a crop of 
fur, for example, might have an interest in seeing the rodent 
population present in a degree that would support the fur- 
bearers in which he was interested. Then too, as you ;re well 
aware, of course, the numbers of rodents as regards many species 
depends upon the life zone where one is working. In general, 
rodents are subject to wide fluctuations in numbers.    These 
are almost periodic in the Arctic Life Zone. Whereas the same 
genus of rodent, if it occurs as far south as the Tropical 
Zone, apparently does not undergo these fluctuations in numbersRAXA. 
The Transition Life Zone, in between,has fluctuations, but they 
are of irregular occurrence as to time and degree. To be more 
specific, black-tailed jackrabbits in eastern Washington are 
well-known to fluctuate in numbers over periods of years; Where- 
as, according to Taylor and Voorhies, the same species in Ari- 
zona does not display variations of this kind or, at least, 
 
(two pages)