Vol. 18, No. 10 
Page 2 
and the Illinois Natural History Survey, has now been completed. The objectives 
of the study were; (1) to determine the immediate (1-3 years postcut) effects 
of clear-cutting on squirrel densities, movement, survival, reproduction, and 
condition; (2) to determine the value to squirrels of small (0.5-1.0 acre) 
uncut islands of trees left in clear-cuts; (3) to determine gray squirrel 
utilization of clear-cuts at 1, 2, 7 > 15> and 20 years postcutting; (4) to 
determine gray squirrel food production in clear-cuts 1, 2, 7, 15 , and 20 
years old; and (5) to determine the utilization by gray squirrels of nest 
boxes placed in clear-cuts 20 and 35 years old. 
We will report the results of this study in subsequent research letters. 
Responses of Prairie Chickens to Habitat Manipulation R. L. Westemeier, 
D. R. Vance 
As previously reported (MWRL 18(8):6), nest success on the sanctuaries 
at Bogota this year was only 41.4 percent--the third consecutive year that 
nest success was below 50 percent. This low rate of success was attributed to 
increased predation on nests, possibly as a result of a reduced food base for 
predators. 
For the past 3 years, when overall nest success was low, a few sanctuaries 
have maintained a high rate of nest success. These sanctuaries (Harks, J. 
McCormack, Fuson, Otis, and Galbreath) were all on the periphery of the 
sanctuary complex and supported lower densities of prairie chickens than those 
sanctuaries in the core of the area (Yeatter, Field, McGraw, Donnelley, and 
C. McCormick). During 1973-75> 190 (32.1 percent) of the nests on sanctuaries 
in the core of the area hatched. During the same period, 11 of the 17 nests 
(64-7 percent) found on the outlying sanctuaries hatched. Apparently, nest 
predation on prairie chicken nests increases as nest density increases. How¬ 
ever, densities of other prey species must also be considered. In 1972, the 
nest density of prairie chickens was the highest ever recorded on the 
sanctuaries, yet nest success was 64.9 percent. But small mammals and ground¬ 
nesting birds were also plentiful. 
Our sanctuaries may be providing "islands" of habitat that support high 
numbers of prey species, thus attracting significant numbers of predators. 
As prairie chickens increase on individual sanctuaries, we may expect in¬ 
creased rates of nest predation. Especially high rates would be expected in 
years when prairie chickens maintain their numbers while other prey species 
dec line. 1 r 
V 
