450 



Illinois Natural History Survey Bulletin 



Fol. 23, Art. 5 



2. Determination of the environmen- 

 tal requirements of Illinois squirrels, the 

 information on this subject to be used in 

 management and restoration practices. 



METHODS OF STUDY 



Illinois, with a north-south length of 

 385 miles, is subject to greater seasonal 

 variations than any other midwest state. 

 In the formulation and administration of 

 fish and game laws, these variations are 

 partially compensated for through the 

 division of the state into the northern, 

 central and southern zones, fig. 1, each 

 comprising about one-third of the state 

 and each representing a difference in sea- 

 son of 6 or 7 days. 



The necessity for determining seasonal 

 variations in squirrel breeding and related 

 phenomena in each of the three zones was 

 recognized at the beginning of the project. 



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Fig. 1. — Map of Illinois showing the three 

 zones on which the game and fish code of the 

 state is based. 



It appeared, therefore, advisable for the 

 senior author to spend the first 10 days of 

 each month in the southern zone, the sec- 

 ond 10 days in the central zone, and the 

 last 10 days in the northern zone, collect- 

 ing and studying during each period a 

 sufficiently large number of fox and gray 

 squirrels to determine seasonal differences 

 in reproduction. Because such a plan, 

 however sound theoretically, was expensive 

 in travel time, only the first year was 

 given to this periodical study by zones. 

 During this time the zonal differences in 

 the seasons of reproductive activity were 

 determined approximately. The second 

 year was devoted to intensive field study 

 on representative central zone areas, on 

 which both fox and gray squirrels oc- 

 curred. 



In general, data on breeding and other 

 seasonal phases of this study relate to 

 the central zone, except where otherwise 

 stated, and practical utilization of the 

 information in the northern and southern 

 zones necessitates appropriate allowance in 

 time. 



Sample material yielding information on 

 squirrel biology consisted of freshly shot, 

 steel-trapped and live-trapped specimens. 

 Study of dead specimens was carried on 

 mainly in several improvised field stations, 

 although some material was examined in 

 Natural History Survey or University of 

 Illinois laboratories. Live-trapped squir- 

 rels were examined in the field, usually at 

 the site of capture. Both fox and gray 

 squirrels were available for study every 

 month for the duration of the project, al- 

 though it was of course impossible to 

 obtain equal numbers of squirrels each 

 month, either in species or sex. Fox squir- 

 rels far exceeded gray squirrels in number, 

 amounting to about 70 per cent of the 

 total examined. 



Each collecting method has its advan- 

 tages. Over much of the study period 

 guns and steel traps were employed simul- 

 taneously. Hunting was most effective 

 during the main mast-feeding months, 

 from mid or late August into October. 

 Trapping was particularly successful 

 during the winter and early spring, 

 when corn was readily taken as bait. 

 Traps were set, uncovered, on logs and 

 each was baited with a half ear of corn, 

 usually impaled on a nail a few inches 

 above the trap. Twenty-five to 50 traps 



