Behavior

Walking, Hopping, Climbing, Etc

Nestlings crawl by pulling with maxilla and pushing with feet until they can stand (DWH). Thereafter, adults and young walk with rocking sideways bipedal motion.

Flight

Foraging flight is moth-like and buoyant with slow, deliberate wing beats. Low wing loading allows for slow, agile, maneuverable flight. Direct and fast wing-pumping flight when defending territories. Will hover with and without wind when hunting. Soar on long broad wings and tail, similar to Buteo hawks. Perhaps same flight used in migration. Often avoids diurnal avian predators and mobbing situations by quickly increasing altitude using soaring and flapping flight (DWH).

Swimming And Diving

Not known, but one male giving distraction display at nest flew and crash-landed in a shallow pond, then used wings simultaneously in a forward rowing motion to swim 10 m to other side, then stood on bank, ruffled feathers, and continued distraction display and vocalizations (DWH).

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

Typically preens by gathering uropygial gland oil in mouth and distributing to feathers. Also uses bill to realign feathers. Scratches head area with talons in zygodactyl or anisodactyl position (see Fig. 4a); also scratches head in flight. Cleans food off bill with toes. Foot maintenance similar to above, but uses maxilla (upper bill) to clean material off toes, talons, and foot pads. Stretches one wing and one leg laterally on same side while standing on opposite leg (Fig. 4b). Stretches two wings over trunk of body by raising them so carpal joints brought close together near back of head (Fig. 4c). Ruffles feathers at termination of preening bout.

Sun-bathes by facing sun, closing eyes, extending head forward, and spreading wings. Dust-bathing done singly or communally: owl stands on ground, leans forward with lowered head, pushes head into soil and flips soil particles over dorsum. Simultaneously, the leading edge of the wings, which are spread on the ground, balance the owl (Fig. 4d); then fluffs plumage vigorously, apparently working soil particles in and out of plumage. Dust-bathing probably serves as feather maintenance and to reduce ectoparasites.

Sleeping And Roosting

Sleeps and roosts primarily on ground; also tree-roosts in winter (Clark 1975, Bosakowski 1986), behavior thought to be influenced by amount of snow on ground, or moisture (Village 1987, Fulk 1976). Also roosts on abandoned stone quarries, gravel pits, wrecked automobiles, and stump piles (Clark 1975). In Middle East, said to roost in large rodent burrows (Voous 1988). In captivity will sleep on ground with closed eyes, relaxed facial ruff and ear-tufts, and wings tucked near body. Similar behavior when perched in exposed areas, except eyes open and the owl more alert (DWH; Fig. 4e). In concealment pose, erects “ear-tufts,” raises white eyebrows and rictal bristles around bill, and changes facial ruff to elongate shape (DWH; Fig. 4f).

Tree roosting occurs singly, communally, or interspecifically—often with Long-eared Owls (Bosakowski 1986). Will form large communal roosts during nonbreeding season, up to 200 individuals on the ground in the same area (Tyler, in Bent 1938). Little known about individual spacing, but communal roosting (flocking) behavior falls into two broad categories: (1) protection from predators and (2) enhanced feeding efficiency (Moore 1977). Undoubtedly also a response to abundant food; in Netherlands over 2,000 Short-eared Owls (and hundreds of hawks) appeared after a vole plague (Voous 1988).

Daily Time Budget

Data limited; probably varies with season, weather, hunger, prey densities, and reproductive status. Clark (1975) reported winter foraging activity began around 14:30 to 15:30 h, but it varied from year to year; early morning foraging also probable. Bosakowski (1989) reported evening departure from day roosts 28 min before to 24 min after sunset, with most (83.3%) departures after sunset. European data suggest more diurnal activity, with 13% of 483 observations between 09:00 to 15:00 h but 66% between 15:00 and 21:00 h (Mikkola 1983). Foraging periods of these owls no doubt reflect prey density and availability, weather conditions, season, and demands of young.

Physical Interactions

During territorial skirmishes with conspecifics, owls fly fast and directly at intruder, pulling up and presenting talons at last moment before collision (Clark 1975). Same agonistic techniques used during interspecific encounters with corvids, falcons, and hawks (see social and interspecific behavior, below). With conspecifics, occasional talon grappling; owls may tumble close to the ground before letting go (Hamerstrom et al. 1961, Carson 1962, Beske and Champion 1971). This behavior perhaps also associated with courtship.

Often use thermal updrafts during skirmishes and rise vertically chasing and interacting with intruders. Exaggerated wing-beats high over body used to display under-wing when patrolling territories and intraspecific interactions (Fig. 4g). Clark (1975) felt this behavior signaled to conspecifics the sex of displaying owl. Males tend to be white ventrally; female buff or rust-colored.

Threat And Appeasement Displays

Threat display when approached by humans consists of dorsal wingspread; owl crouches, ruffles body contour feathers, leans head forward, raises and spreads wings so leading edge faces downward, trailing edge angles up, increasing appearance of size (Fig. 4h; Clark 1975, DWH). These displays typical of adult female at nest and young ready to leave nest.

Adults also use defensive wing-clap to drive off nest intruders. Flight is low on horizontal plane, with wings brought under trunk of body and clapped together (DWH).

Individual Distance

Poorly known, but owls in communal winter and post-breeding season roosts often within 1 m of each other (DWH). In New Brunswick, Canada, 33 nests within 200 ha (Tate 1992). In Montana, 32 nests (30 active simultaneously) within 164 ha, yielding about 1 nest/5.5 ha; minimum distance between 2 nests 55 m (DWH, SML). In North America (Pitelka et al. 1955a, b, Baker and Brooks 1981) and Europe (Lockie 1955, Korpimaki and Norrdahl 1991, Village 1987), numbers fluctuate in direct relation to prey populations; e. g., in Barrow, AK, no owls present in 1951, one in 1952, but 28 nests located in 1953 during a peak in the lemming cycle, with estimated density was about 3–4 pairs/mi²(Pitelka 1955a, b). In one study on Nantucket Is., MA, however, breeding populations remained stable over a 4–yr period (Tate 1992); vole populations can be more stable on islands (see Tamarin 1985).

Territoriality

Wide range in size of breeding territory: Alaska, about 20 ha (Pitelka 1955a); Manitoba, mean 82 ha, range 23–121, n = 6 (Clark 1975); coastal Massachusetts, mean 55.0 ha, range 25–75, n = 9 (Holt and Melvin 1986), also mean 64 ha, range 48–126, n = 10 (Holt 1992). In Scotland, mean 18 ha, n = 7, but changed to mean of 137 ha, n = 2 (Lockie 1955) in apparent response to vole crash; Finland, mean 50 ha, n = unknown (Gronlund and Mikkola 1969); Scotland, mean 83 ha, range 25–242, n = 51 (Village 1987). Territories established and maintained through intraspecific skirmishes and chases. Both Lockie (1955) and Clark (1975) reported breeding territory sizes increased with decreasing prey (vole) densities.

Mating System And Sex Ratio

Seasonal monogamy, but polygamy suspected; e.g., 2 females sharing incubation of 8 eggs from one nest in Finland (Mikkola 1983). No comparable North American data, although two males defending one nest on Nantucket Is., MA in 1985 (DWH). Sex ratio not known.

Pair Bond

Begins late winter as communal roosts disband. Males perform sky dancing displays (see Fig. 5) to prospective females, day or night (DWH). Sky dance consists of song (see Sounds: vocal array) accompanied by aerial acrobatics, including talon grappling (Hamerstrom et al. 1961, Carson 1962, Beske and Champion 1971). Francis Harper (in Bent 1938) described 150 wing stokes/min, as male ascends 60–90 m, then stoops, wing-clapping 8–12 times. Male ascends by flying in small circles to a desired height (30–150 m), hangs in wind or flies forward on fanned wings and tail, give courtship song, followed by shallow stoop with about 5–10 wing-claps under trunk of body. Female usually perches below giving call (see Sounds: vocal array). Male performs several bouts before descending to ground with wings in positive dihedral position, rocking side to side (sashay; Clark 1975). Male passes by female, who sometimes chases male; both birds head to tail descend into grass where copulation apparently occurs (Fig. 5; see DuBois 1924, Clark 1975 for further details). Female observed to join male in courtship flight twice (DWH), but likely occurs more often.

Copulation presumably takes place on ground, but rarely observed. Clark (1975) saw a male catch a vole and solicit a female with song and side to side swaying motion. Female approached male, took vole, turned, and presented herself to male, who mounted with open wings; copulation lasted for about 4 s. Both flew off in different directions.

Duration of pair bond not known, but presumed to be one breeding season. During 3 yr of banding females in Montana, no recaptures recorded (DWH and SML).

Degree Of Sociality

Solitary or communal during the nonbreeding season, but generally considered loosely colonial breeder—perhaps facultative. Communal roosts of about 200 individuals known to form in fall and winter. This behavior probably aides in vigilance (predator detection) and may help individuals find quality feeding sites; may also help to establish pairs at the onset of the breeding season.

Nonpredatory Interspecific Interactions

Mobbed by some smaller passerines, corvids, and gulls (DWH). Brewster (in Bent, 1938) reported Short-eared Owls mobbing Black Ducks (Anas rubripes) and Great Blue Herons (Ardea herodius) “for apparent amusement.” Four Short-eared Owls observed mobbing a Snowy Owl (Nyctea scandiaca) for 1 min (Lein and Boxall 1979). Has mobbed gulls after being mobbed (Mikkola 1983). Two Short-eared Owls participated in mixed species assemblage in cooperative mobbing of a Bald Eagle (Haliaeetus leucocephalus; Humphrey 1989). Observed to mob American Bittern (Botaurus lentiginosus), Turkey Vulture (Cathartes aura), Red-tailed Hawk (Buteo jamaicencis), Rough-legged Hawk (Buteo lagopus), American Kestrel (Falco sparverius), badger (Taxidea taxus), and red fox (Vulpes vulpes) (Clark 1975). Short-eared Owl foraging activity and predation causes nocturnal nest site abandonment and severely limits reproductive success in Common Tern colonies (Holt 1994).

Short-eared Owl also robbed of food by Northern Harriers (Clark 1975, DWH) and Snowy Owls (Lein and Boxall 1979). In contrast, these owls infrequently rob Northern Harriers (Bildstein and Ashby 1975, DWH) and (once) a stoat (Mustela erminea; Wood 1976). Not known to kill other birds of prey.

Kinds Of Predation

Vulnerable primarily to mammalian predation because of open habitat occupied and ground nesting habit. Corvids and jaegers may prey on eggs and nestlings (DWH). Identification of nest predators difficult (DWH). In Montana, 29 (12.3%) of 235 eggs were taken, as were 15 nestlings (8.6% of 174; DWH and SML); mammalian and avian predators suspected. Known avian predators include: Herring Gull (Larus argentatus), jaegers (spp.), Bald Eagle, Northern Harrier, Goshawk (Accipiter gentilis), Peregrine Falcon (Falco peregrinus), Gyrfalcon (F. rusticolus), Red-tailed Hawk, Great Horned Owl (Bubo virginianus), Snowy Owl, and Common Raven (Corvus corax; Brooks 1915, Murie 1929, Sooter 1942, Killpack 1951, Holt 1992, DWH). Great Horned Owl used feathers of Short-eared Owls prey to line its own nest (Able 1990). Mikkola (1976) provides extensive review of interspecific and intraspecific predation in birds of prey of Europe.

Mammalian predators include: red fox, domestic dog (Canis familiaris), and striped skunk (Mephitis mephitis), which find nests or flightless pre-fledged dispersers. At one red fox den in Scotland, remains of eight adult and 68 young Short-eared Owls were found (Watson, in Cramp 1985). (See also Breeding: growth and development).

Manner Of Predation

Known only for avian predators. Diurnal birds of prey and Snowy Owls capture Short-eared Owls in flight and on ground. Jaegers also locate nest and capture dispersed flightless young.