Effects of recreational trails on wintering diurnal raptors along ripariancorridors in a Colorado grassland

Different types of human activity may influence raptors in various ways, po tentially affecting their abundance, distribution, habitat use and producti vity We studied the effects of recreational trails on wintering raptor popu lations in grasslands of eastern Boulder County, Colorado, from December 19 95-March 1996. We conducted strip transacts to survey raptor populations at six study sites. All sites consisted of short and/or tallgrass prairie, an d all contained a riparian corridor. Three sites contained recreational tra ils running adjacent to the riparian corridor (trail), while three sites co ntained no trails (control). Species richness, abundance and perch use were compared between control and trail sites. Species richness was consistentl y greater in control sites. Abundance of total raptors observed was greater in control sites. Abundance of Bald Eagles (Haliaeetus leucocephalus) was greater in control sites, while abundance of Red-tailed Hawks (Buteo jamaic ensis) was similar for control and trail sites. Perching distances from rip arian corridors were greater in trail sites than in control sites. In addit ion, raptors perched along riparian corridors more frequently in control si tes. Results of this study suggest that recreational trails may have affect ed habitat selection of some raptor species in this grassland ecosystem.