Northern Hawk Owl

Surnia ulula

Order:
Strigiformes
Family:
Strigidae
Sections

Behavior

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Locomotion

Walking, Hopping, Climbing, Etc

Rarely walks on the ground; gait restricted to waddling walk and bouncing lope (Cramp 1985a).

Flight

“Their flight is rapid and strong and they are quick and sure in attack. When moving from one perch to another they pitch abruptly down, fly low, and then curve sharply upward to the new outlook” (Roberts 1932c).

Dashes with great speed low through forest and over and around shrubs (Voous 1988b). Usually flies in lower airspace (Cramp 1985a). Also soars and hovers (Thompson 1891). Extremely maneuverable when hunting in densely treed areas; strong and direct flight line (Eckert 1974).

Nero (Nero 1995) described Display Flight as a territorial “bridling” flight display in which an agitated immature male glided on outspread wings with its head raised, followed by circling flight at 15 m; subsequently returned to a primary perch and sang “loudly” intermittently.

Self-Maintenance

Preening, Head-Scratching, Stretching, Bathing, Anting, Etc

Captive birds bathe regularly (Cramp 1985a). Snow-bathing observed (Cade 1952).

Sleeping, Roosting, Sunbathing

Usually rests perched on an exposed treetop, in inclined posture, sometimes preening (Cramp 1985a). Roosts mostly at night on tree branches, not in cavities (Dement'ev and Gladkov 1966, Cramp 1985a); generally close to trunk, hidden by branches or foliage, rarely in a hollow stub (Eckert 1974). Radio-marked individual in Minnesota was found roosting mid-canopy, and occasionally near the top, in tamarack trees in treed muskeg (S. Loch pers. comm.). Nero (Nero 1995) described roosts of 1 individual on 50-ha winter home range; in aspen stand; roosted 1–4 m above snow, most between 1.7 and 2.7 m; on branches close to trunk and possibly in or on broken ends of leaning aspen deadfalls; also on flat surface of abandoned American Robin (Turdus migratorius) nest.

Daily Time Budget

Needs study; primarily diurnal.

Agonistic Behavior

Physical Interactions

Few data. In Minnesota, on 5 Feb 1993, 2 hawk owls (sexes unknown) were observed interacting; one flew at the other, making contact, and the 2 whirled down to the ground with wings outstretched as if their talons were locked together; this sequence was repeated 5 min later, after which the birds flew off (L. Ronning pers. comm.).

Communicative Interactions

Few data from the wild. In captivity, both male and female react to calls or sight of rivals with Screeching Calls; rivals confront each other, sleeking face plumage and staring (Cramp 1985a).

Spacing

Territoriality

Courtship, copulation, and hunting (self-maintenance and for raising young) occur within nesting territory (Cramp 1985a). In Finland, territories established a few weeks before breeding (Mikkola 1983). Thought to have large territories, low breeding densities, and nests isolated from one another. Minimum distance between 2 monogamous males in Finland was 600 m (Sonerud et al. 1987). Inter-nest distances for North America: 2 nests 3 km apart in Wisconsin (Bernard and Klugow 1963); 3 nests within 6–8 km of each other in Alberta (Henderson 1919); 2 nests 1.8 km apart in Alaska (Kertell 1986); 3 other nests in Alaska: 4.8, 7.2, and 8 km apart (T. Osborne pers. comm.); 2 nests 6.4 km apart in n. Manitoba (J. Jehl, Jr., pers. comm.). A male that was paired with 2 females in Finland had a single territory; the 2 females had separate territories (Sonerud et al. 1987). No specific data on territory size in North America. Hunts at least 1 km from the nest (Mikkola 1983). At a nest with 1 young, adults hunted within 100 m of the nest (Cramp 1985a).

Individual Distance

Mutual billing (2 individuals rubbing their bills together) reported for paired birds (Glutz Von Blotzheim and Bauer 1980). Pairs observed sitting side by side, nuzzling and making twittering sounds (Wilson 1993b, R. Gehlert pers. comm.).

Manner Of Establishing And Maintaining Territory

Male establishes territory a few weeks before nesting and attracts a female to the nest site via Advertising Call (see Sounds: vocalizations, above), given mostly during Display Flight (see Locomotion, above) over treetops in territory (Cramp 1985a).

Interspecific Territoriality

Considered tolerant of intrusion on its territory by other birds of prey, including other owls. Competes with other predators of small mammals, but volatility and amplitude of shifts in prey populations likely minimize short-term interspecific competition (Mikkola 1983). In Minnesota, nested within 500 m of nesting Great Horned Owls, Broad-winged Hawks, Northern Goshawks (Accipiter gentilis), Great Gray Owls, Boreal Owls, and Long-eared Owls (Lane and Duncan 1987). In Manitoba, nested 200 m from Great Gray Owl nest (Lang et al. 1991). In Europe, Honey Buzzards (Pernis apivorus), Sparrowhawks (Accipiter nisus), Short-eared Owls, and Great Gray Owls nested within 500 m of a hawk owl nest (Mikkola 1983). During spring 1978, observed chasing a Great Gray Owl as the latter left its nest, knocking it to the ground on 1 occasion; in defending its territory, harassed Broad-winged and Red-tailed (Buteo jamaicensis) hawks (Taylor 1983c). In Alaska, nested within 100 m of an active Common Raven (Corvus corax) nest (T. Osborne pers. comm.).

Winter Territoriality

Apparently variable. Needs study. Although majority of winter sightings are of single birds, such observations are often clumped, with up to 20 birds spaced about 1 km apart; these “concentrations” are ephemeral within and between years (PAD, JRD, T. Swem pers. comm.). Within breeding range, and in more southern areas during invasion years, up to 6 owls within sight of each other for up to 3 wk with no apparent aggressive behavior observed (Kessel 1989, PAD, JRD). Nero (Nero 1995) observed 1 unmarked individual for 90 d within a 50-ha area in Winnipeg, Manitoba.

Sexual Behavior

Mating System

Apparently usually monogamous (Cramp 1985a), although polygyny documented in Norway (Sonerud et al. 1987). In captivity, a male mated with 2 females, both of which laid fertile eggs (Cramp 1985a).

Pair Bond

Male makes circling Display Flights (see Locomotion, above), frequently gliding on stiffly held wings with head held up, over treetops of territory (JRD); claps wings as he flies among trees. Utters Advertising Calls (see Sounds: vocalizations, above) usually from perches, with head slightly raised, exposing black-and-white throat. Male and female on apparently mutually exclusive, but adjacent, territories in late winter; 1 female joined male on his territory 13 d after male initiated Advertising Call (Lane and Duncan 1987).

In captivity, female responds to male's Advertising Call with her Advertising Call; pair later perform antiphonal duetting of Trilled Calls (see Sounds: vocalizations, above), sometimes bowing and touching foreheads, also billing (Glutz Von Blotzheim and Bauer 1980). At beginning of copulation period, male begins courtship-feeding and food-caching, both at the nest and away from it (Glutz Von Blotzheim and Bauer 1980). Male often carries food to nest cavity before feeding female perched nearby (JRD, PAD). Female sometimes summons male with Soliciting Call (see Sounds: vocalizations, above) and wide circling movements of head (Glutz Von Blotzheim and Bauer 1980).

Male and female observed flying close to one another, both “wheeling and turning” as they did; one bird dropped down out of sight, and the other flew off (S. Wilson pers. comm.). Female displaced male from its perch, the male dropped down, wheeled around, and approached female from above and behind as if to copulate; no contact made (S. Wilson pers. comm.). Both birds gave rattle-like calls (see Sounds: vocalizations, Alarm call, above) during interaction, each of different tone and pitch. Female apparently responded to male approach with prey by chattering and flying into cavity, where she continued to vocalize; after 5–10 min, male flew to nest entrance, remained briefly, left prey in cavity entrance; female gave Screeching Call (see Sounds: vocalizations, above), remained in cavity a few minutes, then took prey in bill and flew, eventually caching it (Wilson 1993b).

Copulation; Pre- And Postcopulatory Displays

Copulation typically preceded by loud duetting, initiated by male or female (E. Pletz pers. comm.): “Female utters a series of soliciting calls while in receptive horizontal posture, wings drooped and tail cocked. Male nudges her flank, and flutters his wings while uttering his Trilling Call. Trilling and other calls occur during treading, and after dismounting, the male assumes a rather stiff posture before flying off. Female may also remain in a somewhat stiff posture for a period, making slow tail-pumping movements.”

Duration And Maintenance Of Pair Bond

No data on persistence of pair bond for > 1 breeding season (Johnsgard 1988a), although unmarked birds used same nest site in 2 consecutive years in Alaska (T. Osborne pers. comm.). In captivity, pair bond breaks down by late Sep–Oct, well after young disperse (Aug); male attacks former mates and excludes them from breeding territories (K. McKeever pers. comm.).

Social and Interspecific Behavior

Degree Of Sociality

Solitary and territorial (Cramp 1985a). Little information during nonbreeding season. In se. Manitoba, clumped distribution of winter sightings (see Spacing, above) related to habitat and food availability (PAD, JRD).

Nonpredatory Interspecific Interactions

When surrounded by mobbing birds, individual sometimes makes itself thin and assumes a position of camouflage, with eyes reduced to slits. May extend neck forward and give Screeching Call (see Sounds: vocalizations, above; Cramp 1985a). In Alaska, harassed most often by Gray Jay; also American Robin and Varied Thrush (Ixoreus naevius); robins and thrushes strike perched owls on occasion. Male hawk owl responded aggressively to an attacking American Kestrel (Falco sparverius) by jumping from its perch and presenting its talons as the kestrel dove (Kertell 1986). Generally remains conspicuous and unrestrained (Voous 1988b), however; not easily displaced by smaller birds mobbing it (JRD, PAD).

Observed flying toward and displacing Pileated Woodpecker, in 1 case, after the woodpecker landed in the same tree as the owl (JRD, PAD); this is a prey species, and hawk owls use nest cavities of this woodpecker for nesting. Observed fanning tail and squawking loudly when a Common Raven perched 50 m away (R. W. Nero pers. comm.), but S. Wilson (pers. comm.) reported both species within 40 m of each other with no interactions observed. In nw. Ontario, observed chasing Common Raven several times from deer gut pile on which the owl was feeding; pursued raven for 100 m (S. Walshe pers. comm.).

Predation

Kinds Of Predators

In North America, Great Horned Owl and Northern Goshawk are known predators of adult and fledgling Northern Hawk Owls; Great Horned Owl reported to kill adult roosting hawk owls at night (Eckert 1974). Small, barely visible ear-tufts of this species suggest that arboreal mammals are not significant predators (Perrone 1981), but marten (Martes americana), fisher (Martes pennanti), and weasels (Mustela spp.) kill fledglings (Eckert 1974). In Fennoscandia, Eagle Owl (Bubo bubo) is Northern Hawk Owl's primary predator (17 of 23 records); other predators include Ural Owl (Strix uralensis), Golden Eagle (Aquila chrysaetos), Rough-legged Hawk (Buteo lagopus), Gyrfalcon (Falco rusticolus), Peregrine Falcon (F. peregrinus), and Northern Goshawk (Mikkola 1983) and Great Gray Owl (Strix nebulosa; Lind 2005). The hawk owl's fast, hawk-like flight may explain why it is killed less frequently by diurnal raptors than other owls are (Mikkola 1983).

Manner Of Predation

Marten enters nest cavity and takes eggs or young (Sonerud 1992).

Response To Predators

Adopts concealing Thin-Upright Posture: Flattens plumage, stands erect, and stares at predator (Cramp 1985a). A male hawk owl stiffened and called several times when a Red-tailed Hawk flew rapidly over the nest; the male owl remained perched (Kertell 1986). Hawk owl observed flying into shelter upon sighting a Northern Goshawk in its territory (Mikkola 1976). Kertell (Kertell 1986) observed a male hawk owl attempt to intercept a goshawk flying toward its nest tree; the hawk owl flew toward it, flew past it without striking it, and continued to pursue it until it was 40 m away from the nest.

Bill-snapping in defense is rare. Will attack humans and mammalian and avian predators by repeated aerial attacks at the head (Eckert 1974, Lane and Duncan 1987). After young have left the nest, female may perform Distraction-Lure Display on the ground: Calls (sreee sound), droops wings, and flutters along the ground for several minutes (Leinonen 1978).

Recommended Citation

Duncan, J. R. and P. A. Duncan (2014). Northern Hawk Owl (Surnia ulula), version 2.0. In The Birds of North America (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.356