September, 1945 



Brown & Yeager: Squirrels ix Illinois 



511 



The degree to which they use each type is 

 determined, at least partly, by the kind 

 and age of the trees in an area. Squirrels 

 were sometimes found by the present writ- 

 ers in young stands, in some cases where 

 cavities were very scarce; but the animals 

 were more common in older, cavity-con- 

 taining timber. There is no doubt of the 

 superiority of the mature forest range, but 

 the fact that both fox and gray squirrels 

 built leaf nests even where cavities were 

 present suggests that the highest quality 

 habitat must possess the possibility of both 

 types of nest. The writers believe that 

 either type of nest may supply the essential 

 year around nesting requirements of either 

 species. 



Dens 



On the large expanse of Illinois black 

 prairie, where only the fox squirrel is im- 

 portant, there is an acute shortage of tree 

 cavities suitable for denning purposes. In 



this region, a few bottoms, occasional 

 woodlots and Osage orange hedgerows 

 supply the main tree cover. The hedges 

 contain very few cavities, and Osage 

 orange leaves are not well suited to nest 

 construction. Although both bottoms and 

 woodlots of the black prairie region con- 

 tain numerous trees with cavities, the total 

 acreage of such units is so small and their 

 distribution so poor that great inadequacy 

 of dens prevails in the region. In one 

 Illinois study, Hesselschwerdt (1942) 

 demonstrated that boxes made of lumber 

 serve very usefully in meeting the den 

 shortage in the fox squirrel habitat of the 

 black prairie, fig. 32. Use of these boxes 

 is discussed further in the section on 

 "Management." 



Many river bottoms and wooded upland 

 areas, particularly in southern parts of the 

 state, are well supplied with den trees. 

 Most cutover areas, as a result of the des- 

 tructive practice of cutting to smaller 

 diameter limits, have been stripped of 



big. 32. — Xesi box Miitahle tor sciiiinels in an Osage orange hedge, Champaign County, 

 1940. A screech owl is sitting in the entrance of the box. An acute shortage of tree cavities 

 suitable for denning purposes exists on the Illinois black prairie. 



