The red-tailed hawk (_Buteo jamaicensis_), the long-eared owl (_Asio otus_), the great horned owl (_Bubo virginianus_) and the crow (_Corvus brachyrhynchos_) fed on _Microtus_. All four birds were fairly common permanent residents on the Reservation (Fitch, 1952:25). The low density and the strict territoriality of the red-tailed hawk (Fitch, _et al_, 1946:207) prevented it from exerting any important influence on the population of voles, even though individual red-tailed hawks ate many voles. Predation by the long-eared owl was especially heavy; remains of voles were identified in 72 per cent of its pellets examined. Korschgen (1952:39) found remains of voles in 70 per cent of 704 pellets of the long-eared owl. The reason for the heavy diet of _Microtus_ seems to be that both the owl and the vole are especially active at dusk. A group of long-eared owls, living near the edge of Quarry Field, probably exerted an influence on the density of the local population of voles because of the high ratio of predator to prey animals. The crows ate some, and perhaps most, of their voles after the animals had died from other causes. Other birds, mostly raptors, occurring in northeastern Kansas and reported to prey on voles include the sharp-shinned hawk (_Accipiter striatus_), Cooper's hawk (_A. cooperi_), red-shouldered hawk (_Buteo lineatus_), broad-winged hawk (_B. platypterus_), American rough-legged hawk (_B. lagopus_), ferruginous rough-legged hawk (_B. regalis_), marsh hawk (_Circus cyaneus_), barn owl (_Tyto alba_), screech owl (_Otus asio_), barred owl (_Strix varia_) and shrike (_Lanius excubitor_) (Korschgen, 1952:26; 28; 34; 35; 37; McAtee, 1935:9-27; Wooster, 1936:396).