We studied nest parasitism of greater prairie-chickens (Tympanuchus cupido pinnatus) by ringnecked pheasants (Phasianus colchicus) as a possible contributing factor in the decline of an isolated population of prairie-chickens in Jasper County, Illinois. Both species nested in small, scattered grasslands maintained on prairie-chicken sanctuaries. Incidence of parasitic laying by pheasant hens in prairie-chicken nests increased from 2 to 43% between 1970 and 1983 and remained high through 1987. Nest success (:1 host-egg hatching) did not differ (P = 0.33) between 60 unmanaged parasitized nests (43%) and 602 unparasitized nests (51%). However, success of 14 parasitized prairie-chicken nests managed by removal of pheasant eggs (86%) was greater (P = 0.02) than for 24 unmanaged parasitized nests (46%) during 1983 and 1985-87. Hatchability of fertile prairie-chicken eggs was less (P < 0.01) in parasitized nests (77%, conservatively) than in unparasitized nests (94%), because of earlier hatching of pheasant eggs, increased embryo mortality of prairie-chickens, or increased nest abandonment. Large clutches of prairie-chicken eggs typical of early nests were more likely (P < 0.001) parasitized than small clutches laid later. Factors correlated with rate of nest parasitism included numbers of pheasant cocks (P = 0.01) and numbers of pheasant nests (P < 0.001) found each year. Although pheasant control apparently eliminated nest parasitism during 1988-94, prairie-chicken numbers continued to decline. Without management intervention to control pheasants on sanctuaries, the survival of this isolated, remnant flock of prairie-chickens may be in greater jeopardy.
T h e low er C in cin n a tia n an d su bjacen t beds are suitable for stu d y b y lith ostratigraphic m ethods, an d h a ve been studied an d classified on th at basis. L o gs o f the clastic ratio (shale-plus-siltstone to limestone) are most useful, bu t logs o f the stratigraphic in d ex an d o f ab u n d an ce o f the kinds o f lim estone are helpful and particu larly significant in paleogeograp h ic considerations. T h e C y n th ia n a Form ation o f the O h io V a lle y is represented b y the P oint Pleasan t Lim estone M em b er, ly in g d irectly ben eath the classic E d en and g rad in g n orthw estw ard into the shalier B rom ley tongue. N icholas, R iv e r Q u a r r y , an d R ogers G a p are all rejected as stratigraphic units. T h e Point Pleasan t is a th in -to m ed iu m -bed d ed biogen ic lim estone w ith shale h a vin g a clastic ratio of ab o u t i and alw ays less than 5. T h e limestones are rather free o f c la y an d silt, an d some contain intraform ational conglom erates, subm arineslum p features, an d a few m udcracks. T h e m em b er is at least 75 feet thick w ith in the O h io V a lle y outcrop belt. T h e basal part contains a conodont assem blage o f p rin cip ally E u ropean forms; th e rest contains lon g-ran gin g indigenous species. T h e E d e n F o rm ation o f the typ e region is in terbed d ed shale an d lim estone ly in g betw een limestones o f the P oint Pleasan t M e m b e r an d the F airviewF orm ation. I t contains no subordinate lithic u nits; Fu lton , E con om y, S o u th gate, an d M c M ic k e n are rejected as stratigraphic units. T h e clastic ratio throu gh o u t the base o f the form ation is ve r y h ig h ; above the base the lower beds h a ve a ratio o f ab ou t 2 at eastern localities. From th at va lu e the ratio g en erally increases u pw ard a t a n y lo cality an d n orthw estw ard at an y level to as m u ch as 15 in m id-form ation w est o f C in cin n a ti. T h e E d en limestones are thin -or m ed iu m -bed d ed , b u t the shales ran ge from lam in ae to v e r y th ick beds. T h e m acrofaun a is d om in ated b y O n n iella , Thaerodonta, and several bryozoans. C o n o d o n t Z o n e I is coextensive w ith the form ation, w h ich in creases in thickness from 150 to 280 feet northw estw ard across southwestern O h io . T h e shales an d siltstones o f these form ations are m assive or lam in ated and fissile an d consist m ostly o f fine an d m ed iu m silt. A b o u t 15 per cen t is calcite;illite, chlorite, and q u artz are the m ost a b u n d a n t acid-resistant minerals.T h e limestones fall into a few coherent groups th a t differ in texture, state of fossil debris, an d " insoluble" con ten t; all are a t least p artly biogenic. A shoal, ly in g southeast o f the crest of the C in c in n a ti " arch ," th at served as a partial barrier to detritus from the east a n d southeast, an d was lo cally crow d ed w ith ben th ic organisms, controlled the p etrograph y o f the shales an d limestones an d the stratigraphy o f the C y n th ia n a an...
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