Vol. 19; No. 12 
Page 3 
of any squirrel population. Fox squirrels appear to have what is known as a 
linear social heirarchy, with adults dominant over juveniles and males usually 
dominant over females. Unlike gray squirrels, which often reach population 
densities that necessitate large-scale emigrations when food supplies fail, 
fox squirrels seem to control their density through an annual emigration of 
juveniles, usually in early summer or in autumn. Thus, fox squirrel populations 
that are not subject to heavy and sustained annual harvests by hunters are 
typically stable in size from year to year and are composed mostly of adult 
squirrels. 
This is the case for our two study areas in Vermilion County, Illinois, 
where we are testing the effects of artificial nest boxes on a fox squirrel 
population. 
What happens when more shelter is provided for a squirrel population that 
presumably is utilizing all suitable existing tree dens? Will the constraints 
of food supplies and the existing social structure allow for an increase in 
population size? It seems reasonable to suppose that added adequate shelter 
in the form of nest boxes should benefit the subordinate juvenile segment 
most, at least initially. 
Nest boxes provide more protection from predators and inclement weather 
than do leaf nests. However, we were without knowledge of the existing social 
structure when we placed nest boxes in the study areas; thus, at some locations 
leaf nests may be utilized instead of den boxes because the leaf nests are 
sited near the centers of an individual squirrel's home range, where conflicts 
with other squirrels would be minimized. This factor may be particularly 
important for the subordinate juveniles. 
Thus far, nest boxes seem to be more important to juvenile squirrels 
than to the adult population. We have checked nest boxes for squirrel 
occupancy for three winters on our study areas and have found proportionately 
more juvenile squirrels present than would be expected on the basis of our 
fall 1ivetrapping. We found that 41.7 percent (20/48) of the squirrels 
captured in boxes were juveniles, whereas orily 27*4 percent (52/190) the 
population that we livetrapped was comprised of juvenile squirrels. For 
adults, 25.0 percent (12/48) of the box captures were females and 33.3 percent 
(16/48) were males. We found 36.3 percent of our livetrapped samples (69/190) 
to be adult males and females (same percentage for both sexes). Thus, nest, 
boxes appear to attract adult males in about the same proportion as they exist 
in the population. The boxes appear to attract proportionately fewer adult 
females and proportionately more juveniles than exist in the wintering squirrel 
population. 
Responses of Prairie Chickens to Habitat M anipulation R. L. Westemeier, 
D. R. Vance 
The problems associated with the establishment of pheasants on the 
prairie chicken sanctuaries may be listed as follows: 
