| Summary: | The Short-eared Owl (Asio flammeus) and the Northern Harrier (Circus cyaneus) are listed as endangered in Illinois (IESPB 1992). Both species of raptor have become regular winter residents at Prairie Ridge State Natural Area (PRSNA) in Jasper Co., and have recently been observed nesting there in the spring. Apparently, management practices implemented to benefit the endangered Greater Prairie Chicken (Tympanuchus cupido) have benefitted these endangered raptors and other species of grasslandassociated birds as well. Small mammals constitute the major prey items for Short-eared Owls and Northern Harriers (Colvin and Spaulding 1983, Collopy and Bildstein 1987). Analysis of contents of pellets indicates that this is true at PRSNA, where voles and bog lemmings constitute the majority of prey items (J. Walk, pers. comm.). An abundant supply of diurnal and crepuscular small mammals, in addition to extensive areas of grassland and wetland habitat suitable for roosting and nest sites, is necessary for successful overwintering or nesting of these raptors. Management practices at PRSNA such as the planting and maintenance of blocks of different types of vegetation undoubtedly affect the dispersion, abundance, and productivity of populations of small mammals (e.g., Getz 1985). Further, many species of small mammal exhibit pronounced annual or multiannual fluctuations in abundance (Taitt and Krebs 1985). Some habitat types
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