Illinois Natural History Survey - University of Illinois

Non-resident Prairie Chickens in Illinois

Illinois' native prairie chickens numbered about 50 individuals in spring 1994. Only 5 or 6 remnant boomers (males) and an unknown number of hens remained in Jasper County, but at least 18 cocks and 7 hens persisted in Marion County. Later this summer, we received unverified reports of prairie chickens on two separate farms enrolled in the Conservation Reserve Program in Marion County, so perhaps more birds are there than was thought.

Current numbers contrast with millions of prairie chickens found statewide in the mid to late 1800s when prairies gave way to agriculture. Dramatic population increases on sanctuary grasslands during the late 1960s to the mid-1980s were followed by dangerous downward trends in numbers. Decimating factors .included intensified land use on private land near sanctuaries and intense interactions with pheasants (now under local control by Illinois Department of Conservation (IDOC) managers). Also, long-term (1963-91) declines in fertility and hatch rate of prairie chicken eggs may represent the classic symptoms of inbreeding depression. A 1992 action plan by IDOC for genetic management called for

translocations from large populations to enhance genetic variability and numbers of Illinois prairie chickens. So far, three releases have been made and are now being evaluated.

New residents in spring 1994 in Jasper County included at least l of 15 radio-marked Minnesota hens released in August 1992. Other hens with dead radios might have been present from the 1992 release. In 1993, the verified hen lost her brood (the only radioed brood in 1993) within three weeks after hatching, but she fledged young this year.

A second release of Minnesota origin included 8 cocks and 4 hens (all radioed) in August 1993. Two of these cocks were successfully translocated as five-week-old chicks with the brood hen; one of the two males became a dominant boomer in 1994.


Praire Chicken Boomer Strutting His Stuff

The mother's nest was depredated on a sanctuary about l00 yards from her 1993 release site. Another hen from the four released in 1993 apparently fledged at least 1 chick this year.

Surprisingly, l Minnesota cock showed up in spring 1994 among booming grounds (courtship and mating sites) in Marion County some 40 miles from the 1993 release site in Jasper County.

A third release in early April 1994 on booming grounds in Jasper County involved 96 birds from Kansas composed of 50 hens (23 radioed) and 46 cocks (6 radioed). Four of the 6 radioed Kansas cocks became active boomers among the mix of 5 to 6 Illinois cocks, 2 Minnesota cocks, and 10 unradioed Kansas cocks. Thirteen (56%) of the 23 radioed hens stayed on or near the sanctuaries in Jasper County, 10 of the 13 were verified as nesters, and 7 of the 10 nests hatched young. Of the 7 radioed brood hens, 3 evidently fledged young. Extrapolation from the performance of the radioed birds suggested that 3 to 4 unradioed Kansas hens reared young and that 27 unradioed Kansas cocks may have participated in booming. The number of boomers (Illinois and Minnesota combined) nearly tripled after the release of Kansas cocks, but the extrapolated estimate of 27 unradioed cocks may be an overestimate.

Fertility and hatch rate of total eggs was high (99 percent and 94 percent, respectively) for a sample of 18 prairie chicken nests in 1993-94; 15 of these nests involved radioed hens and most were probably hybrid clutches. None were parasitized by pheasants, in contrast to parasitism rates that reached 43% in the mid-l980s. Indeed, no pheasant eggs occurred in 47 prairie chicken nests observed during 1988-94, following intensive pheasant control implemented by IDOC in 1986 in Jasper County.

We were pleased with the performance of the Minnesota and Kansas birds translocated to Illinois. Expectations based on similar studies (except that no prairie chickens were already in place) in other states were exceeded and therefore are encouraging. Genetic and demographic enhancement of remnant Illinois stock appears to have been successful. On the downside, the last vestiges of possible racial distinction in Illinois prairie chickens will likely cease to exist with the 1994 breeding season. The unexpected appearance of a Minnesota cock in Marion County some 40 miles from the Jasper County release site suggests that the genetic transformation may have included both of Illinois' remnant "populations." Nevertheless, we are guardedly optimistic that Illinois can continue to have wild populations of prairie chickens. Ongoing efforts to develop a minimum of 1,500 acres of sanctuary grasslands in both Jasper and Marion counties (3,000+ acres, total) continues to be a basic critical need for the two restored grassland ecosystems.


Ron Westemeier and Roger Jansen, Center for Wildlife Ecology

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