Vol. 18, No. 7 
Page 3 
Both areas showed an increase in the squirrel populations from December 
to March. This increase may be partially due to the greater ease of trapping 
squirrels in late winter and early spring, when food supplies are much lower 
than in early winter. The percentage change in the population indices for a 
10-day trapping period in December and a 7“day period in April for Area A was 
+ 86.3 for the number of captures per thousand trap nights. This value for 
Area B was +104.1. If the 10-day trapping values in April for Area A are used, 
the increase on Area A was 47.8 percent. Thus, Area B, the control area, had 
an increase in population indices that was similar to that on the experimental 
area. 
The effects of winter feeding on the population estimates on Area A are 
not precisely determined. In both trapping periods, more squirrels were caught 
on the experimental area than on the control area. However, chi-square tests 
on the number of squirrels caught per thousand trap nights yielded no significant 
difference (£>0.05) between Areas A and B in December for 10 days of trapping 
and in April for 7 days of trapping. However, one effect of supplemental 
feeding may have been to attract squirrels to the area that were not there 
prior to the feeding. On the basis of captures per thousand trap nights in 
April, 51*6 squirrels were caught on Area A that were not captured in December 
as compared with 35*7 on the control area. Winter feeding may therefore have 
influenced some squirrels to move onto the area, at least for feeding purposes. 
Responses of Prairie Chickens to Habitat Manipulation R. L. Westemeier, 
D. R. Vance 
During the spring of 1975* 437 people visited the prairie chicken booming 
grounds in Jasper County on a reservation basis. Beginning with 56 people in 
1966, when records were first kept, the number of visitors has gradually in¬ 
creased each spring and has totaled 2,714 to date. Duplications probably amount 
to about 10 percent. This spring, 60 groups representing 16 different univer¬ 
sities or colleges, 9 different Audubon clubs, and various other agencies and 
interested individuals were involved on 29 mornings. We try to limit the 
number of individuals to 20 per morning. Illinois supplied 59 percent of the 
visitors this spring, Indiana 22 percent, Ohio 10 percent, and lesser numbers 
came from Pennsylvania, Missouri, Tennessee, Kentucky, and Washington, D. C. 
As in past springs, visitors aided the research project by recording their 
observations on standard forms during 78 blind mornings (one or more observer 
per blind per morning). Observer records indicated that the period of 29 
March through 13 April was the peak period of hen visitation on the display 
grounds. The first copulation in 1975 was noted on 1 April and was followed 
by a peak in mating activities between 6 April and 14 April. A total of 55 
copulations were reported by observers in blinds this spring. 
Marsh hawks continued to be the most common source of disruption on the 
booming grounds; harriers were noted on 61 of the 78 blind mornings this spring. 
There was no evidence of kills of prairie chickens by harriers, but among such 
