Vol. 24, No. 10 
Page 3 
The desertion rate for prairie chicken nests in Marion County and other 
areas of Illinois (3.0%) with few or no pheasants was similar to that at Bogota 
for 1963-63 (3.2%) when pheasants were absent or rare. This further implicates 
the pheasant as a factor in reduced productivity of prairie chickens at Bogota. 
Trends in mean numbers of hatched eggs per nest and the percentage 
hatchability of prairie chicken eggs also appear related to pheasant abundance 
(Table 3). In both Jasper and Marion counties, when few or no pheasants were 
present, the mean number of hatched chicken eggs per nest was about 11 and 
hatchability exceeded 92%. These data are essentially identical with nest data 
collected by Dr. Ralph F.. Yeatter in the 1930's (pheasants essentially absent) 
in Jasper County. At Bogota, the data for prairie chickens show a decline from 
11.1 to 9.5 hatched eggs per clutch and from 93-3 to 02.6% hatchability from 
the 1963“63 period to 1901. 
Fertility (X = 04.4%, range 91.0-97-2%) has been relatively stable over the 
same 19-year period. Thus, embryonic mortality, not infertility, has caused the 
decline in egg hatchability. 
A comparison of current data from Bogota with data from Jasper County in 
the pre-pheasant years and from Marion County suggests that nesting hens have 
altered their behavior, such as reduce attentiveness during incubation, because 
of harassment by pheasants. Thus, pheasants may also be a principal factor in 
the increased embryonic mortality noted at Bogota. 
Table 2. Comparison of unsuccessful prairie chicken nests parasitized by 
pheasants and desertion of prairie chicken nests with population levels of 
pheasants in Jasper and Marion counties. 
Year(s) 
Est. number 
of pheasant 
cocks in area 
Prairie chicken 
nests 
Sample 
size 
% Unsuccessful 
parasitized 
% Deserted 
(not parasitized) 
JASPER COUNTY 
1963-68 
0-1 
62 
0.0 
3.2 
1969-73 
307 
1.6 
7.5 
1974-80 
14-26 
299 
2.7 
4.7 
1981 
43 
25 
8.0 
8.0 
MARION COUNTY AND OTHER AREAS 
1964-31 
0-1 
33 
0.0 
3.0 
