Great Horned Owl

Bubo virginianus


STANFORD LOCATIONS:

Several pairs are resident on campus. Nests in tall trees (such as eucalyptus), often in old Red-tailed and Red-shouldered hawk nests. A pair usually nests in the arboretum.
  
Nest
Location
Nest
Type
Eggs
Mating System
Dev.
Parental Care
Primary &
2ndary Diet
Foraging
Strategy
ABANDONED
NEST
F-M
I: 26-35 DAYS
SEMIALTRICIAL 2
30 feet - 50 feet
(15 feet - 70 feet)
 CLIFF
F?
2-3
(1-6+)
MONOG?
F: 35 DAYS
MF
BIRDS
SM VERTS
INSECTS
BREEDING: Conif or decid forest and woodland, swamp, orchard, park, riparian forest, semidesert. 1 brood.
DISPLAYS: Male performs noisy aerial courtship display; ritually feeds female. Pair bill, bob, call, and click.
NEST: In abandoned tree nest of raptor, corvid, occ squirrel; also tree cavity, cave, crevice, stump, and on ground in log, among rocks; of sticks, moss, hair, shredded bark, rootlets, etc., lined slightly with feathers and down. Perennial.
EGGS: Dull white. 2.2" (55 mm).
DIET: Esp rabbits and rodents, pheasants, quail, passerines, occ fish, amphibians, reptiles, scorpions. Mainly nocturnal, but also hunts crepuscularly. Ejects pellets.
CONSERVATION: Winter resident. Occ uses nest box.
NOTES: Incubating bird often snow-covered in n; early eggs may freeze. Population density in n tracks snowshoe hare density; disperse when hare numbers crash. Young hatch asynchronously; rapidly develop ability to regulate body temperature, fly at 63-70 days, fed for several months. Adults perform distraction display. Daytime roost in dense conif near trunk. Most do not breed before second year. Arctic populations eat more birds. Cache prey; defrost frozen cache by "incubating" it ("prey thawing").
ESSAYS: Irruptions; Pellets; How Owls Hunt in the Dark; Mobbing; Brood Reduction; Breeding Season.
REFERENCES: Adamcik and Keith, 1978; Marti, 1974; Turner and McClanahan, 1981.

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Except for Stanford Locations, the material in this species treatment is taken, with permission, from The Birder's Handbook (Paul Ehrlich, David Dobkin, & Darryl Wheye, Simon & Schuster, NY. 1988).