Fcologic 
Chicago 
 
 
      ROWI-TABIZ L iSCUSSIONa 
Game and Fur Population Mechanisms 
 
   Introduction by Uldo Leopold 
 
 
This discu, sion is intended to illus rate three facts, more or less new,
in 
population  esearch. It is confine    to game birds and game and fur mammals,

not out of   ck of interest in othe groups, but because time does not suffice

to cover a w  er bracket. 
 
The three new   cts are: 
   1.  Species s m to shift in th ir populati6n behavior patterns. 
 
 
2. Reproduct 
 
3. Sex and 4 
    mechanism 
 
 
re often best measured indirectly. 
mises to yield new clues to population 
 
fta in Behavior 
 
 
A decade ago we had our specia  neatly classified into cyclic and non-cyclic

groups. Grouse, rabbitsoand      as, and some fur bearers were cyclic, others

not. A fewlspecies exhibited    regular peeks called irruptions. These three

types of behavior (cyclic, fl t, a d irruptive) came near being considered

as species characters. What' aved      from that error was the tact, even
then 
visible, that grouse and rab   ts were yclic ,At high latitudes but not at716wer

ones. 
Today these neat categories ýre all but sh   tered, and it is the
animals them- 
selves that did the 'sha ,ttering. I 'cit'e some ases whic .h look lik'ý
shifts in 
pattern. 
The IPheeant, Low. During he lapt 'three years th bottori has fallen out
of 
this hitherto tflat"t spec ,s. The decline wa   simu' eMneous in timing
and almost 
transcontihental in scope. Bven the fabulous D.kotas     ye felt the pinch.
what 
are we dealing with? * 
 
Sportsmen say foxes. Th6 decline did coincide in time wit a transcontinent&l

high in foxes, but the f4x hypothesis is seemingly ruled ou' as a major cause

by the fact that' pheasanis declined on foxless habitats heret  ore supporting

excellent stands of bircs, such as Pelee Island in Lake Brie. 
 
Some local 2esearches acribe the decline to agricultural changes, 'such as
high- 
speed mowers (which are destr'uctive to nests), or too much new plowing for
grain. 
It -appears to, me that agricultural changes would produce a spotty abundance
map, 
rather than a monotone of scarcity.- Thud new plowing for grain would daiiage

habitats which are short of cover, but improve others which are short of
food. 
The most reasonable hypothesis dealing with visible factors is bad nesting

weather, but lethal 'weather would hardly hit with continental uniformity
for