PARASITISM OF GREATER PRAIRIE-CHICKEN NESTS BY RING-NECKED PHEASANTS

We studied nest parasitism of greater prairie-chickens (Tympanuchus cu pido pinnatus) by ring-necked pheasants (Phasianus colchicus) as a pos sible contributing factor in the decline of an isolated population of prairie-chickens in Jasper Country, Illinois. Both species nested in s mall. scattered grasslands maintained on prairie-chicken sanctuaries. Incidence of parasitic laying by pheasant lens in prairie-chicken nest s increased from 2 to 43% between 1970 and 1983 and remained high thro ugh 1987. Nest success (greater than or equal to 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 g reater (P = 0.02) than for 24 unmanaged parasitized nests (46%) during 1983 and 1985-87. Hatchability of fertile prairie-chicken eggs was le ss (P < 0.01) in parasitized nests (77%, conservatively) than in unpar asitized nests (94%), because of earlier hatching of pheasant eggs, in creased embryo mortality of prairie-chickens, or increased nest abando nment Large clutches of prairie-chicken eggs typical of early nests we re more likely (P < 0.001) parasitized than small clutches laid later Factors correlated with rate If nest parasitism included numbers of ph easant cocks (P = 0.01) and numbers of pheasant nests (P < 0.001) foun d each year. Although pheasant control apparently eliminated nest para sitism during 1988-94, prairie-chicken numbers continued to decline. W ithout management intervention to control pheasants on sanctuaries, th e survival of this isolated, remnant flock of prairie-chickens may be in greater jeopardy.