Vol. 25, No. 1 
Page 2 
Table 1. Mean concentrations of metabolites of chlorinated hydrocarbon 
Insecticides detected in pheasant chicks collected in Ford and Livingston 
counties, 1576-77. The average age of pheasant chicks sampled was 3-5 weeks 
ages ranged from 2 days to 10 weeks. 
M 
X (ppm)— 
Frequency 
Heptachlor epoxide 
20 
.0191 
20 
p,p'-DDE 
20 
.0203 
19 
o,p'-nDE 
20 
.0090 
7 
Oieldrin 
20 
.021k 
20 
£ x concentrations represent whole body samples for 13 chicks <26 days of 
age, and liver-muscle-heart-brain samples for 7 chicks >27 days. 
Ecology and Ma nagement of Squirrels - W-66-R 
C. M. b* i xon, 
L. P. Hansen 
V'ildlife biologists cite reproduction, survival, and immigration as factors 
that strongly affect numerical change in populations. Unfortunately mucl 2 
each of these demographic parameters impacts densities is seldom evaluate . 
make such an evaluation, a sensitivity analysis was performed on data gathered 
during a 7-year study of fox squirrels. 
Ve calculated means and coefficients of variation for survival, reproductive, 
and immigration rates during the 7-year study period. When the mean values were 
put into a rate-of-change equation (Table 2), an average rate of increase coud 
be calculated. The deviation from this mean rate of increase, produced when 
of the demographic parameters was varied (over the range of values °^ e ™ e . . 
durinq the 7-year study) while the other parameters were he d constant at their 
mean values, was an indication of the impact of this variable on numerical 
change. This process was repeated for all of the demographic parameters. 
Survival of fox squirrels from birth to 0.5 year varied most from year to 
year and potentially had the largest impact on density change. Survival or 
adults also strongly affected numerical change; however, adult survival varied 
little relative to the other demographic parameters. The other demograpnic 
parameters (see equation) had lesser impacts on density change than survival of 
nestling and adult squirrels. 
These results are from an unexploited fox squirrel population; results from 
exploited populations might differ somewhat. Our results indicate that to 
maintain sizable squirrel populations, -nagement should first try to ..icre.se 
survival of young and adults, because they most strongly impact density changes. 
