Illinois Natural History Survey Reports

              1
R e p o r t s
January/
February 1997
No. 343
I N S I D E
Predicting Juvenile
Fish Abundance From
Characteristics of the
Spring Flood
2
European Corn Borer
Management: Past and
Present
3
Soybean Disease Diag-nosis
Going High Tech
4
New Publications and
Educational Materials
5
Species Spotlight:
American Beech
6
The Naturalist's
Apprentice:
What Tree is That?
7
Continued on back page
I LLINOIS
NATURAL
HI STORY
S U R V E Y
Prairie chicken hen
at INHS sanctuary in
southern Illinois.
The fi rst of scattered sanctuar-ies
for prairie chickens were
acquired with extremely limited
funds in the early 1960s by the
Prairie Chicken Foundation of
Illinois and The Nature Con-servancy.
Little information
was available on the amount of
grassland that would be required
to preserve the species in Illinois.
Also, estimates of the number of
individuals of a species that con-stitute
a minimum viable popula-tion
ranged from 50 to 500; the
latter allowed for evolutionary
processes to continue over the
long term.
Initial goals called for 1,000
acres in each of two counties (Jas-per
and Marion) to develop and
maintain two breeding populations
of about 500 birds from extant
remnant fl ocks. A sex ratio of ap-proximately
50:50 was assumed.
These goals were believed to be
Grassland for Prairie Chickens: How Much
is Enough? realistic be-cause
prairie
chicken num-bers
soared
from about 80
to 400 (40-206
cocks) between
the mid-1960s
and early
1970s in Jasper
County. This
dramatic re-sponse
occurred
with only 660
acres of sanctu-ary
grassland
available to the
birds by spring
1972. Neverthe-less,
the sanctu-ary
goals were
raised to 1,500 acres in each of
two counties in 1973 to allow for
probable intensifi cation in farming
practices.
By spring 1982, a similar en-couraging
response occurred in
Marion County with an increase
to about 230 prairie chickens (116
cocks) with only 450 acres of sanc-tuary
grassland. For 19-year peri-ods,
densities averaged 93 and 83
cocks per square mile of managed
land for Jasper and Marion coun-ties,
respectively. Thus, for nearly
two decades, 100 prairie chicken
cocks per square mile of sanctuary
grassland appeared to be a realis-tic
density goal for Illinois. Two
sanctuary systems, each with 1,500
acres, well-situated, properly man-aged,
and well-used by the birds,
appeared to be at least minimum
goals with which to achieve long-term
preservation of the species.
Unfortunately, land acquisi-tion
goals were not attained and
the favorable responses did not
continue into the current decade.
By spring 1994 in Jasper County,
the count of prairie chickens on
booming grounds had declined
to six Illinois cocks plus two
translocated Minnesota cocks.
This brink of extinction oc-curred
despite a new record of
nearly 1,000 acres of sanctuary
grassland available in 1992 to the
prairie chickens at Bogota. The
situation was not much better in
Marion County where the cock
count ranged from 9 to 18 in the
past fi ve springs with approxi-mately
500 acres of sanctuary
grassland.
Photo courtesy of T.J. Ulrich
Prairie chicken sanctuaries in
Jasper County, Illinois.