Vol. 23, No. 5 
Page 3 
disperse evenly throughout suitable habitat. Studies by other researchers 
indicate that gray squirrels often occur at higher densities than fox squirrels. 
Vindicated in last Month's newsletter, the density regulatory effect of the 
social system in fox squirrels may preclude certain management efforts. Sue 
efforts £!lld more likely produce positive results in gray squirrel populations. 
Responses of Prairie Chickens to Habitat Manipulation - W-66-R R.L. Westemeier 
Prairie chicken populations in Illinois showed an overall gain of 55% 
betweeViV springs of 1979 and 1980 (MWRL 2 3 (4):2-3). A popular rationale for 
this increase is that the unusually mild winter of 1979-80 resulted 
winter mortality of prairie chickens. This view assumes that weather-related 
winter mortality is highly significant in the population ecology of remnant 
flocks of Illinois prairie chickens. Analysis of spring and fa '! c 
for booming grounds on the Bogota Study Area does not support this hypothesis. 
Since 1966, booming grounds at Bogota have been censused approximately 
biweekly from October through December, weekly from January through late March, 
and almost daily from late March through late April. Cock counts on booming 
grounds usually peak in spring during the first week of April and in fall, 
between late October and mid-December. 
Since 1966, correlation of spring counts (dependent variable) with the 
previous fall counts (independent variable) has been highly significant 
(r ■ 0.979, P^O.OOl). Thus, the spring population at Bogota since 1966 has 
been closely dependent on the fall population; 96 % of the variation in s Pr'"9 
numbers has been associated with fall numbers. Little variation in the spr ng 
populations could possibly relate to differential winter mortalityji.e., wint 
storm related mortality has not been a significant factor for prairie chickens 
at Bogota. 
By contrast, the relationship of fall counts (dependent variable) with the 
previous spring counts (independent variable) indicates a lower correlation 
coeWcLn? of 9 ,- = 0.814 (P-0.001). Thus, whereas 66% of the var at,on ,n fal 1 
numbers relates to variation in spring numbers, approximately one-third of the 
fluctuation in fall numbers of prairie chickens is unexplained and relates to 
events of the nesting and brooding periods, or both. 
Over the past 14 years at Bogota, changes in prairie chicken abundance have 
primarily reflected variations in net productivity. Once again, the implication 
is that quality nest-brood habitat must continue to be emphasized in managing 
prairie chickens in Illinois. 
Apparently, winter food and cover have been adequate at Bogota even during 
the severe winters of 1976-77, 77-78, and 78-79- Provision of additional winter 
food and cover has never been seriously considered in our management progr . 
However, the above correlations do not negate the possibility that winter food 
patches, such as unharvested corn or soybeans, strategically located, mig 
promote a more favorable dispersal of the Bogota flock. Specifically, the birds 
at Bogota continue to concentrate on the yeatter-Field-McGraw sanctuary unit. 
A better distribution of the chickens in winter might lead to higher net 
productivity. 
