Northern Prairie Wildlife Research Center
STATUS: Rare to locally fairly common; once reduced in numbers almost to the point of extinction in the United States. Year-round irrigation of agricultural land has improved habitat conditions in recent years.
HABITAT: Inhabits open country around freshwater marshes, moist meadows, alfalfa fields, and cultivated bottomlands, with scattered clumps of trees. In the western Sierra Nevada in California, found below 1,000 feet in blue oak-savannah, digger pine-oak, and riparian deciduous types.
SPECIAL HABITAT REQUIREMENTS: Trees with dense canopies for nesting near a permanent water source and an abundant population of voles (Microtus spp.).
NEST: Nests in oak, willow, eucalyptus, cottonwood, or other hardwood trees, from 18 to 59 feet above ground, usually near a marsh, streambank, or canal, and areas where voles are abundant. With good vole populations, breeding pairs need a minimum of 20 acres around the nest site for hunting.
FOOD: Searches for food by flying and hovering at less than 100 feet above ground. Feeds primarily on voles, but also eats other small mammals, small snakes, lizards, frogs, and large insects such as grasshoppers, beetles, and crickets.
REFERENCES: Brown and Amadon 1968, Heintzelman 1979, Oberholser 1974a, Terres 1980, Verner and Boss 1980.