September, 1945 



Brown & Yeager: Squirrels in Illinois 



467 



gray squirrel migration of small propor- 

 tions in Vermont in 1935. According to 

 the reports of numerous authors, the mi- 

 grations covering the most territory, as 

 well as involving the most individuals, oc- 

 curred before the twentieth century. 



Dispersal 



According to Baumgartner (1940), the 

 most extensive and important movement in 

 fox squirrels "is the traveling associated 

 with the annual readjustment of popula- 

 tions. This dispersal movement occurs 

 between August 10 and September 15. 

 J'he distances traveled at this time average 

 about two or three miles, although two 

 long records of 14 and 8 miles respectivel\ 

 were secured. This movement is respon- 

 sible for the annual restocking of over- 

 hunted areas." 



Allen (1943) indicates that a popula- 

 tion shuffle occurs in Michigan fox squir- 

 rels. He states (1943) that "... it 

 appears that increased activity among 

 squirrels begins in late August, rises to a 

 peak in late September, and is over by the 

 middle of December." 



Of the reasons for dispersal Baumgart- 

 ner (1943rt) writes: "The cause of this 

 movement is controversial. The motivat- 

 ing factor is usually considered to be 

 population pressure correlated with a 

 shortage of food, yet it occurs when the 

 food supply is greatest, almost simul- 

 taneously with the maturing of the nut 

 crop. The moving squirrels are more 

 noticeable when the population is high, 

 and the writer believes the movement re- 

 sults from intra-species intolerance. This 

 view is partially substantiated by the fact 

 that no record of excessive fox squirrel 

 populations, either in the literature or in 

 the field, could be authenticated. Seven 

 such reports were investigated but none 

 showed more than two squirrels per acre." 



Our evidence indicates that in Illinois a 

 dispersal occurs in both fox and gray squir- 

 rels during the fall. Continuous and in- 

 tensive live trapping on the Wade area 

 over a 10-month period prior to August 

 8, 1942, resulted in the capture and mark- 

 ing of most if not all resident squirrels, 

 since only one unmarked animal, a 1941 

 summer juvenile (female), was taken 

 either by trapping or hunting during the 

 period between July 12 and October 15, 



1942. Ihis individual was trapped on 

 August 5, and it is likely that the squirrel 

 had only recently moved onto the area 

 from a woodland to the east. On August 

 8, 1942, the writers shot two fox squirrels 

 (Nos. 11 and 26) and seven gray squirrels 

 (Nos. 1, 5, 9, 13, 26, Zi and 50) on the 

 Wade area. No unmarked animals were 

 among these squirrels. In the period Oc- 

 tober 15 through 17 the senior writer shot 

 13 additional specimens, 5 fox squirrels 

 and 8 gray squirrels, of which 1 fox and 2 

 gray individuals were unmarked. They 

 were 1942 spring juveniles, and therefore 

 subject to trapping and marking had they 

 been present during the last 8 to 10 weeks 

 of trapping. It is believed that these 

 three animals had moved onto the area 

 during the period of August 8 through 

 October 17. Other than these three 

 spring juveniles, six unmarked 1942 

 summer juveniles (one fox, live gray) 

 were collected in mid October, 1942, but 

 these may have been young born on the 

 area and too small to be taken in live traps 

 prior to August 8. 



CONDITION 



Weight and length measurements w^ere 

 taken of most squirrels collected, and in- 

 formation on diseases, parasites, deformi- 

 ties and pelage development was recorded 

 when observed in the specimens. 



Weight 



Weights were obtained for a total of 

 706 fox squirrels and 317 gray squirrels. 

 The data are given in table 9. In adults, 

 weights were recorded by sex, but in 

 juveniles the weights of the two sexes 

 were lumped. 



As indicated in table 9, there were no 

 significant differences in weight between 

 male and female adults in either species. 

 Allen (1942, 1943) found female fox 

 squirrels in Michigan to be slightly larger 

 than males. A point of interest in the 

 present stud>' is that of size in juveniles 

 at the time the\ began to enter hunters' 

 bags in July. Spring juvenile fox and 

 gray squirrels at that time had an average 

 weight of 1.28 pounds and 0.84 pound, 

 respectively. By late October or Novem- 

 ber, the spring juveniles of both species 

 had reached approximately average adult 



