Vol. 25, No. 4 
Page 2 
Ecology and Management of Squirrels - W-66-R C. M. Nixon, 
" L. P. Hansen 
In our studies of the effects of nest boxes on fox squirrels, we rarely 
found females of breeding age in nest boxes but frequently found adult males in 
them. Because adult males are usually dominant in social encounters with 
females, we speculated that adult males may exclude breeding females from nest 
boxes. 
To better assess shelter selection by the various age classes, we collected 
squirrels from leaf nests and nest boxes in late winter 1978 from our study 
area in Vermilion County, Illinois. We destroyed all leaf nests and emptied 
nest boxes; we then livetrapped the area intensively for 2 weeks and assumed 
that captured squirrels were sheltering only in tree cavities. 
Breeding females were as likely to be found in leaf nests and tree 
cavities as adult males (Table 1). Subadults also have access to tree cavities, 
presumably the shelter favored by all segments of the population. Subadult 
and adult females were most often found in tree cavities, whereas males were 
found equally as often in all 3 shelters (Table 1). 
We believe that breeding-aged females avoided our nest boxes because of 
inherent deficiencies in the design and placement of the boxes. Leaf nests used 
to shelter preweaned young are usually found 50“70 feet high in trees. We 
believe this is an attempt to prevent predation of young by raccoons, opossums, 
and the climbing snakes, which are less likely to reach high-placed nests. If 
our boxes had been placed higher in the tree canopy, we probably would have 
improved the occupancy rate for breeding-aged females. However, we would have 
had difficulty checking these boxes and capturing squirrels in them at night 
when we conducted many of our nest box checks. 
Male fox squirrels, without the demands of rearing young, can be less 
discriminating in nest site selection. They appear to tolerate other males 
more than females tolerate other females; subadult and adult males were 
frequently found in the same nest in winter. Females were always solitary 
when captured in a shelter, except for an occasional instance of a female 
found with 1 or 2 juveniles, presumably her young. For maximum benefit for 
fox squirrels, nest boxes should be placed as high in trees as possible and 
anchored solidly to the tree. 
Table 1. Shelter use by fox squirrels on 2 areas near Danville in late February, 
1978. Fox squirrels were captured or shot in nest boxes and leaf nests; live¬ 
trapped squirrels were assumed to be using tree cavities after removal of boxes 
and leaf nests. 
