September, 1945 



Brown & Yeager: Squirrels ik Illinois 



513 



trees with cavities. Selective cutting, es- 

 pecially if light, results in little harm to 

 squirrel range, either temporary or per- 

 manent. 



The best den trees in Illinois are the 

 oaks, maples, American elm, white ash, 

 beech, sweet gum and, in extreme southern 

 Illinois, cypress and tupelo gum. The in- 

 herent soundness of such trees as Osage 

 orange, Cottonwood and the hickories, even 

 when mature, eliminates them as impor- 

 tant den producers. The oaks, partly be- 

 cause of their abundance and state-wide 

 range, are easily the most important den- 

 tree group, fig. 33. 



The physical characteristics of cavities 

 in relation to squirrel denning require- 

 ments were not studied h\ the present 

 writers. Baumgartner (1939/>') and Allen 

 (1942, 1943) reported in some detail on 

 this subject. Both writers found that 

 squirrels maintain den entrances at a 

 suitable size in growing trees by gnawing 

 the green cambium each year. Allen 



(1943) found that fox squirrels used al- 

 most any size or depth of hollow, some- 

 times stuffing with leaves those too large 

 for comfort. He also found that certain 

 individuals may establish and use specific 

 dens for long periods, occasionally for the 

 entire life of the animal. Four or i\vt 

 usable cavities per acre are probably ample 

 for any permanent squirrel population. 

 The present writers found considerable 

 evidence that one squirrel, male or female, 

 may use concurrently two or more cavities 

 or nest boxes. 



Of the protective value of cavity nests, 

 Allen (1942) aptly states: 'Trom the 

 management standpoint, hollow trees are 

 doubtless desirable even though squirrels 

 can live without them. They protect the 

 animals from hunters, natural enemies, 

 such as raccoons and owls, and severe 

 weather." The present writers, in agree- 

 ment with Allen, have observed that good 

 tree cavities afford, during storms and ex- 

 treme cold, a protection that may be 



Fig. 34. — Typical fox squirrel leaf nest in oak, Cook County. (Photo by Gordon S. Pearsall. 



