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Walking, Hopping, Climbing
Adults comfortably bipedal, and will walk to settle on a ground roost. Also walk around ground to inspect where prey may be hidden. Young entirely bipedal, and coordinated prior to fledging; can run when needed. All can hop and use outstretched wings for balance. Climbing, in classic sense, not known, but probably capable of climbing/walking on leaning objects. Two flightless females flushed from their nests by walking when researchers approached, rather than flying normally (DWH). See also Appearance.
Varies, depending on circumstances; can be leisurely, similar to other species of large owls. In general, flight is somewhat buoyant and similar to that of the Short-eared Owl. When chasing avian prey, conspecifics, or predators in defense of territory, flight is fast, straight, strong, and somewhat falcon-like. When high in the air, can glide long distances like a Buteo hawk, or can glide from a high perch to capture prey on the ground. Hovers, and kites, when hunting in high winds over tundra or other open terrain. Flies low with interrupted wing beats to sweep and grab prey with foot. When defending nests, circles threat from high in the air, dives at high speed, generally attacking from behind (see nest defense). Frequently looks behind and over back when flying.
Adults swim well, but not voluntarily – usually when injured. Prior to fledging young, regularly and voluntarily swim across small creeks and ponds during their pre-fledging movements (DWH). Flightless young will opt to swim when being threatened by predators and researchers. In doing so they use both wings in a rowing motion. Similar observations reported as one flightless young swam about 15 m (Parmelee et al. 1967).
Preening, Bathing, Etc.
Not well reported. In the wild, individuals frequently observed to preen body and flight feathers by pulling feathers through the bill (Parmelee 1992, DWH). Use one foot to scratch or wipe face, head, and bill, apparently for self-maintenance (DWH). Frequently stretch wings and legs. Early reports of drinking and bathing are contradictory (Tulloch 1968, 1969), but known to bathe on breeding grounds (Parmelee 1992; details needed), and elsewhere (Mebs and Scherzinger 2000). Observed to snow bathe in Minnesota, in similar motions as water bathing (D.L. Evans, pers. obs.).
A pair of captive Snowy Owls observed by Watson (1957) spent much time preening, wing stretching, and cleaning their bills and faces by wiping them with their feet. Females preen nestlings, usually on the back of the head and neck where nestlings cannot reach. Nestlings appear to preen each other on the same areas, but function not known (DWH). After feeding, both sexes often wipe their bills and faces with one foot. Snow reported to be used in cleaning (P. Kerlinger pers. comm., in Parmelee 1992).
Unlike species such as Ptarmigan (Lagopus spp.) that burrow in snow to gain relief from the Arctic winter, Snowy Owls are not known to burrow, or use snow for thermal advantages. However, they will take relief from wind and storms by hiding behind objects (DWH).
Sleeping And Roosting
Few data; needs study. Probably different for breeding vs. nonbreeding or wintering individuals. Observations from blinds and review of film clips (DWH) indicate females are generally vigilant at the nest. During incubation, females have been observed to sleep, then quickly awaken to look around. Overall, the breeding female does not appear to sleep much, but may sleep more when her mate roosts nearby and guards the nest (DWH). When not breeding, males and females appear to sleep while roosting, sometimes waking to preen or look around.
In Barrow, AK, Snowy Owls appear to gain relief from wind when roosting behind mounds. Roosting atop mounds occurs at lower wind speeds than roosting on the leeward side of mounds (DWH).
Daily Time Budget
Few data; needs study. Time budgets change with season, weather, prey densities, and breeding/non-breeding status. In general, said to hunt in evening in winter (Saxby 1863), mornings and afternoon (Manniche 1910), or all hours, but less active at noon and mid-night (Watson 1957). These reports are in general agreement with others (Hohn 1973, Weir 1973, Young 1973). Winter hunting observations over 30 yr indicate activity period usually begins at dusk and continues well into the night (N. Smith, pers. comm.). Similar conclusions reached by other winter researchers, but all acknowledge activity is sometimes dictated by weather, hunger, or other variables (D. Evans, D. Holt, T. McDonald, H. Pletz, M. Stoffell, D. Zazelenchuk).
In Barrow, AK, during one season, 11 captive (10 female, 1 male) and 8 wild Snowy Owls were studied under 24 h of Arctic daylight, for a comparison of their daily activity cycles (Shields 1969). Further recording was conducted after the sun began to set in August. The author reported on sleeping, dozing, quiet, mild, active, eating, drinking, bathing, and hyperactive behaviors for captive owls and wild owls. The captive owls had a continuous food supply. During 24 h of daylight, the captive owls showed a cyclic activity period and were most active from 21:00-08:00. The wild owls were active throughout the 24-h period but once August arrived and the sun began to set, both captive and wild owls were more active at sunset and in darkness. During rain, however, the wild owls reduced activity to sleeping and dozing (Shields 1969).
Near Calgary, Alberta, Canada, 15 Snowy Owls were observed for 138 h over two winters for activity patterns and energy budgets (Boxall and Lein 1989). Behavioral categories included; alert, rest, preen, and other. Only daytime observations were recorded from 08:00 to 18:00. The owls were too difficult to track after sunset when they were also active. Results were similar during the two season study, but a more apparent bimodal activity pattern emerged in the second season, as the owls were more active (alert and flying) from 08:00-10:00 and 16:00-18:00, with an inactive (resting) period from 10:00-16:00 (Boxall and Lein 1989). Perch height and attempts to capture prey peaked more in late afternoon (16:00-18:00). Overall, the owls spent 98% of the daylight hours perched, and were alert more often than resting. The authors concluded the owls' activity patterns apparently coincided with activity patterns of prey species (small mammals).
Territorial males known to chase and fight fiercely with territorial intruders (Watson 1957, Taylor 1973). Breeding females also know to defend territories against other females (Cramp 1985). Extent of such interactions is not well known and has not been quantified, but appears to be infrequent.
Reported encounters between nonbreeding Snowy Owls are equally scarce, except that Evans (
Evans, D. L. 1980a. Vocalizations and territorial behavior of wintering Snowy Owls. Am. Birds no. 34:748-749.
Evans 1980a) observed a few frequent threatening behaviors, and also chases and mid-air clashes with clasped talons. During a two-season winter study near Calgary, Alberta, male Snowy Owls tended to be nomadic, while females maintained exclusive territories using postural displays, threats, and direct aggression (Boxall and Lein 1982b).
Intraspecific communication is influenced by a variety of factors, including: age, sex, breeding and social status, and environmental factors.
Males use Hooting Displays (Figure 4) to help establish and maintain territorial borders. In these displays, males “face-off” at a distance (usually several hundred meters), bowing forward with each call, tail lifted. Use of these displays decreases after territories are established; generally rare after early to mid-June (Taylor 1973).
In threat display, individual lowers the front of its body, stretches its head low and forward, with wings partly extended, and feathers of head, back and flanks raised (
Watson, A. 1957b. The behaviour, breeding, and food-ecology of the Snowy Owl Nyctea scandiaca. Ibis no. 99:419-462.
Watson 1957b). Both young and captive adults exaggerate this display when cornered. If forced back, birds finally lie on their backs, striking with talons and bill. On the breeding ground it is usually the male that postures, although when hooting the wings and feathers are less elevated. Females posture to a lesser extent both on and off the nest.
Plumage color (white is commonly known to have high reflectance values) may aid in visual displays/ social signaling (Bortolotti et al. 2011). Snowy Owl reported to have high reflectance in the visible range (400-700 nm) of the electromagnetic spectrum (Reynold sand Lavigne 1981), but see Potopav and Sale (2012), who determined that Snowy Owl do not reflect in the UV or near UV spectrum.
Spacing varies among individuals and may be influenced by age, sex, aggression, food resources, and individual tolerance. Spacing is also influenced by season (i.e. breeding vs. non-breeding). Although Snowy Owls (along with Long-eared Owls (Asio otus), and Short-eared Owls) are sometimes referred to as colonial or semi-colonial breeders, this habit of loosely clustered breeding does not fit the true definition of colonial breeding, such as in seabirds.
On wintering grounds, reported to be solitary territory holders. In other wintering areas, many roost within the same field, and even within a few meters of each other, suggesting communal roosting. See also Territoriality, below.
On the breeding grounds, in one year from Barrow, AK, non-breeders often associated in loose groups with 20-30 owls occupying an area of ~ 20-30 ha (Pitelka 1955b). Indeed, during years of high lemming abundance and high nest density, young non-breeding males roost in loose association (“bachelor areas;” DWH). These owls appear non-territorial. Rarely are females within such groups. In contrast, adult males (ID based on all white plumage) establish individual territories, whether breeding or not (DWH).
Defining territories is difficult. Territories can change seasonally or annually in relation to prey densities, perhaps topographic features, and result in varying nest densities. For example, in Barrow AK, on a 213 km2 study area in a high lemming year, 54 nests were found; in a low lemming year, there were no nests in this area (DWH). Also in Barrow, AK, territories are primarily exclusive, with few territorial skirmishes observed, and there appears to be some tolerance of conspecific males at territory boundaries (DWH). Not all territories are circular; some may be more linear, or a combination of forms. Needs study.
At Churchill, Manitoba, Shelford (1943) reported a nest about every 3.2 km. In Barrow, AK (Pitelka 1955a), densities of breeders and non-breeders during late Jun/early Jul were 5 owls per 1.6 km2. Distances between pairs were about 1.6 – 3.2 km, with territories 5.2 – 10 km2. The closest breeding pairs/nests reported for North America: ~ 800-1600 m (Hart l880; Brandt 1943; Pitelka et al. 1955a).
In low lemming years, successful nesting correlates with territories having more abundant lemmings (“hot-spots”; DWH), and with increased territory size (Wiklund and Stigh 1986); in addition, adults often move nest-departed chicks to better hunting grounds (DWH).
In one year on Southhampton I., Nunavut, average distance between 6 nests in one area was 3.5 km; and between 3 nests from another area 2.5 km. Shortest distance between two nests was about 1 km (Parker 1974). Overall nest density was estimated to be 1 nest/22 km2. In the following year, no owls were seen in the same area – apparently owing to a decline in the lemming population.
On Banks I., Nunavut, Manning et al. (1956) estimated Snowy Owl density to range from 1 owl/2.6 km2 or more in good lemming years to 1 owl/26 km2 in low lemming years. On Wrangel I., Russia, Snowy Owl nest numbers and lemming population's fluctuations are highly correlated. From 1969-1987, 36 nests were found in 100 km2 during “good” lemming years; in “poor” lemming years no owls bred (Litvin and Baranyuk 1989, in Vaughn 1992).
In other studies from Wrangel I., Russia (Meuyshina 1997) estimated owl density at 0.11-0.7 km2 during breeding season across the island. In her sample plot over 1990-1995, she reported nest densities of 0.15-0.4/km2, with increasing and decreasing densities related to lemming abundance.
More data are needed, but the ‘boom and bust' nomadic nesting strategy of Snowy Owls in relation to lemming density gives a wide range of spacing behavior (DWH).
Winter territory size may have biases because researchers often do not calculate areas used by owls hunting at night. One of the first studies of winter territory was by Kieth (1960). He color-marked 5 owls and followed them from 36-57 d at Horicon Marsh, WI. He reported overall territory sizes of about 2.6, 2.1, 1.3, 0.8, and 0.5 km2, respectively, for these 5 birds.
During a two-season winter study near Calgary, Alberta, male Snowy Owls tended to be nomadic, while females maintained exclusive territories using postural displays, threats, and direct aggression (Boxall and Lein 1982b). Most males moved through the study site in 1-2 d, some stayed from 3-17 d, with a mean of 6.6 (n = 7). Although some females also moved through the study area, many stayed. Of identifiable females, their stay ranged from 3-80 d, with a mean of 44.8 d (n = 15 d); mean territory size for 9 females was 154.6 ha (range 152-162, n = 3) in 1976/1977, and 266 ha (range 127-450, n = 6) in 1977/1978. Mean territory size for juvenile females was 407.5 ha (n = 2) and for adult females 195.2 ha (n = 4) (Boxall and Lein 1982b).
In Montana, both territorial and communal wintering behaviors have been observed (Holt and Zetterberg 2008). For example, 31-35 Snowy Owls wintered in a 2.6 km2 area, with most birds occurring within 500 m2. The owls roosted communally, near, and next to each other, often in groups of 5-10 individuals. Similarly, in 2011, 15 Snowy Owls wintered together, roosting in a community on housetops and similar structures within yards. They often roosted within 20 m of each other, occasionally side-by-side (DWH). The majority of these owls appeared to be males and a few females in their first year of life, although plumage suggested some were older females (DWH).
At Logan Airport (East Boston, MA), many individuals stay and maintain winter territories, while a small percent of individuals move extensively. For example, 11 of 56 color-marked owls moved from initial places of capture at Logan Airport 155-555 km away from this site during the same winter, covering six states (Smith 1997). One individual, banded at Logan Airport on 09 Nov 1991, and was re-sighted 19 Dec at Bath ME, 197 km northeast. On 24 Jan 1992 it was back at Logan Airport. The same bird was sighted on 25 Feb 1992, 115 km southeast of Logan Airport at Martha's Vineyard, MA. It was sighted one day on 26 Feb 1992 at Charlestown, RI, 92 km east from Martha's Vineyard. It was again spotted on Boston Harbor's, Little Brewster I., on 16 March, 125 km northeast of Charlestown, RI, and finally moved 6 km from the island back at Logan Airport on 23 March. It left the airport on 20 May 1992.
Monogamy. Seasonally socially monogamous, with few cases of polygyny. Not known to establish long-term pair bonds, as would be expected with a highly migratory, nomadic species. In Barrow, AK, of 239 nests found from 1992-2014, 232 cases of social monogamy and seven cases (14 nests) of social bigamy discovered (DH; see below). Genetic research is also needed to confirm behavioral observations for extra pair paternities.
Polygamy. On Baffin I., Canada, one bigamist male bred successfully with two females, and sired 15 young that fledged (Watson 1957). Bigamy also noted in Norway (Hagen 1960) in which the first (primary) female nested 16 d before the secondary female, and the nests were 1.3 km apart. In a very unusual situation on Fetlar I., UK, Snowy Owls bred outside the normal breeding range from 1967-1975. Based upon detailed observations, it was believed the same pair nested in 8 consecutive years (Robinson and Becker 1986). Two instances of bigamy were reported. In 1973 and 1974, the male mated with two females, each of which laid eggs. In both years, the male fed the original (primary) female, but not he secondary female. The secondary female, however, was younger, was previously banded as a nestling on Fetlar, and believed to be an offspring from the original pair. Zero young survived for the secondary female. In 1975, the original female disappeared and was replaced by the secondary (banded) female. The pair raised four young. If true, this would represent a known case of incest in Snowy Owls. No nesting occurred after 1975.
In Barrow, AK, not all bigamist relationships are successful, due to variety of reasons.
Polyandry or helping behavior not convincingly reported. In Norway, two males were reported to feed the same female and her young (Host 1935, in Mikkola 1983). No cases of polyandry or helping from Barrow, AK (DWH).
Generally occurs late Apr to mid-May; seasonal only. Not known which sex first arrives on the breeding grounds. Male likely initiates the courtship display. Courtship behavior best described from a study at one nest on Bathurst I. (Taylor 1973), but see also Watson (1957), Tulloch (1968), Robinson and Becker (1986).
Male performs near or far away from a prospective mate. Male's aerial display (Figure 5) marked by exaggerated wing beats, especially on the upstrokes, creating a shallow undulating, bouncy courtship flight, with the wings set in acute dihedral “V”, high over the back. Male often carries prey (i.e. lemming) in its bill. At termination of the flight, male gains altitude and sets wings again in “V” position, and glides gently downward. No vocalizations heard. The overall flight, seen from a considerable distance, has been described as moth-like; display results in a wave-like undulating flight. Flight display diminishes as nesting progresses. Female not observed to engage in flight display.
Upon landing in a snow-free area, or old nesting area, male begins ground display (Figure 6). Sometimes ground displays are performed independent of aerial displays. Male often drops prey from bill; stands erect with wings partially spread, stretched backward from the wrist, and held high. Some males walk in small circles, showing sides and back of body, but not facing female. At some point the male leans forward with head lowered and tail partially fanned; frequently peers around its wings towards the female. Flashing wings appear to attract female, who flies in. Male keeps wings raised and back oriented to the female; keeps prey in front, as if hiding it from the female. Ground display lasts only a few minutes, rarely 5 min. No vocalizations heard. Similar observations reported by others (Murie 1929, Pitelka 1955a, Watson 1957, Tulloch 1968).
A female assumes essentially the same posture before, during, and after copulation (
Taylor, P. S. 1973a. Breeding behavior of the Snowy Owl. Living Bird no. 12:137-154.
Taylor 1973a; see Figure 7). While perched, she leans fairly far forward with partly raised tail, wings held loosely at sides, and body feathers generally slightly ruffled. This attitude elicits displays by males not only before but also following copulation. Evidently vocalizations may or may not be a regular part of these behaviors, a subject that merits additional study. Males mounting females have often been witnessed, but details of the copulatory act are lacking, especially on what constitutes successful sperm transfer.
Apparent winter courtship behavior has been reported (see Boxall and Lein 1982c), but it is rare and no prey deliveries or copulation have been reported. Species not reported to migrate or arrive in pairs on breeding grounds. Migration, nomadism and wide-scale wandering in search of food probably keep Snowy Owls from mate and site fidelity; consequently pair bond is believed to last one season (DWH), but study is needed.
Not known. In most reports, species appears to be socially monogamous with few instances of polygyny; broods of bigamist relationships remain apart and do not interact (Watson 1957, DWH).
Social and Interspecific Behavior
Degree Of Sociality
Not fully understood. On breeding grounds adults maintains exclusive territories. However, younger non-breeding adults, particularly males, often concentrate in loose groups away from territorial adults (Pitelka 1955b, DWH). Also, previously believed to be solitary and maintain individual territories outside the breeding season, with few exceptions (Parmelee 1992, see Territoriality). However, a recent study suggested Snowy Owls do form communal roosts in winter and may be highly social (see Holt and Zetteberg 2008).
Interactions With Other Species / Association With Non-Predators
Several studies in North America support the observations that geese, ducks, and shorebirds gain protection from predators when nesting near Snowy Owls (Murie (1929, Parmelee 1972, Lepage et al. 1996, Tremblay et al. 1997, Ebbinge and Spaans 2002, DWH). On Wrangel I., Russia, small colonies of Snow Geese (Chen caerulescens), Brent Geese (Branta bernicla), and Common Eider (Somateria mollissima) are known to nest in association with Snowy Owls. And when the owls do not breed, these small goose colonies disappear from the island (Syroechkovsky 1970, in Vaughn 1992). Nonetheless, Snowy Owls will kill and eat adults and young of bird species nesting within their territory, and the zone of protection around the nest, suggesting trade-offs to this behavior (Robinson and Becker 1986, DWH).
Kinds Of Predators
On the breeding grounds, avian and mammalian species of potential threat include: eagles, hawks, falcons, jaegers, gulls, ravens, fox, wolves, bears, and wolverines, among others. Adult Snowy Owls have few natural predators, and are rarely killed by other predators. In one report, a Snowy Owl grabbed a Peregrine Falcon fledgling from a cliff, and an adult Peregrine chased the owl and killed it with one stoop and strike (Nelson 1887, in Bent 1938). There is one observation of an Arctic fox killing an adult male Snowy Owl (see Menyushina 1994a, b, c). Two records of possible predation by Bald Eagle (Haliaeetus leucocephalus) and Golden Eagle (Aquila chrysaetos), but direct observation not observed (Campbell and Preston 2009).
Potential nest predators almost certainly include bears and wolves. Pomarine Jaegers rarely attack and kill chicks (DWH).
Response To Predators
In Barrow, Alaska, some owls do not attack researchers during nest checks, but do engage in attacks if potential predators wander into the nest area. For example, owls non-aggressive towards researchers were observed to turn aggressive if Glaucous Gulls (Larus hyperboreus) flew into nesting areas (DWH). Owls engage them with attacks and chases. Owls also will abandon attacks on researchers and redirect attacks to foxes or dogs that wander into the nest area (DWH).
Breeding males are almost always within sight of the nest if food is plentiful, but exceptions occur. Thus, males can be vigilant against predators and hunt at the same time. Nest defense includes: flushing from the nest, distraction displays, vocalizations, wing feigning, and attacks. Although males conduct most nest defense, females will also engage, depending on circumstances and individual female disposition.
On the breeding grounds, known to aggressively attack Eskimo dogs, caribou, fox, wolves, bears, gulls, jaegers, raptors, and others that approach close to nests (see Parmelee 1992, DWH). During winter, known to attack and kill other raptors (see Food Habits).
Most reports relate to people (i.e. researchers) at nests or observations of Snowy Owls on wintering grounds. Individual Snowy Owls range from shy to aggressive depending on the time of year (i.e. breeding verses non-breeding). Serious wounds to humans have been reported (Barth 1950, Sutton and Parmelee 1956, in Parmelee 1992, DWH). Most attacks are initiated from the rear of the threat, suggesting the owls perceive the eyes of intruders. Few attack straight on (DWH). Attacks may start when an intruder is 50-100 m from the nest, but attacks are most fierce usually at nests with chicks, or when an intruder is near a nest with flightless chicks.
Much variation in nest defense among individuals and pairs. During studies in Alaska, individual nest defense differences were noted by Murie (1929). Some males attacked while other did not. Most females vocalized from a distance. Males that did attack often gave-up after several minutes and roosted nearby. Some aerial attacks never make contact, and some individuals seemed to become accustomed to nest visits (Murie 1929).
On Fetlar I., UK, non-predatory grazing animals such as sheep and ponies were attacked as they wandered close to nests (Tulloch 1969). In Barrow, AK, similar observation when caribou (Rangifer tarandus) wandered near nests (DWH). In these circumstances, fear of trampling eggs or chicks may engage the owls, leading to attacks, or the birds may simply fail to discriminate between animals that constitute potential threats and those that do not.
Nest defense observations from Barrow, AK (DWH), agree with much of Wiklund and Stigh (1983). First line of nest defense is for female to flush from a long distance at the sign of approaching danger; e.g., in 1995 females from 30 nests flushed from about 380 m (range 121-780, n = 212 observations); 1996, females from 19 nests flushed from about 415 m (range 57-732, n = 86 observations).
Other nest defense behaviors include; attack, bark, hoot, distraction display, scream/whistle, and perch distance. Of 706 visits to 30 nests in 1995 the following behaviors recorded: attack - males 151 (21%), females 32 (4.5%); bark - males 554 (78%), females 469 (65%); distraction display - males 54 (7.6%), females 101 (14.3%); hoot - males 142 (20%), females (< 1%); scream/whistle - males 21 (3%), females 107 (15%). Analysis of 1999 and 2000 data indicated that pairs in which males attacked and females gave distraction displays fledged more chicks than pairs that did not (DWH).
Numerous researchers observed similar behaviors with similar results. Unfortunately, it can be difficult to separate different behaviors as they move along a continuum of all behaviors (DWH). Some females will join male in nest defense, and attack in the presence of dispersed young (DWH). Males rarely engage in wing feigning or distraction display (Sutton in 1932, also in Bent 1938, Sutton and Parmelee 1956, DWH). Males and females sometimes engage in threat posture with head low and wings somewhat spread, with feathers of head, back and flanks raised (Watson 1957), and occasionally charge forward (Watson 1957, Tulloch 1968, DWH), but this behavior is more common in females and can turn into retreat, trying to lure a threat away from the nest. Both sexes used distraction displays, with female often feigning injury. Upon completion of successful nest defense adults quickly resume parental responsibilities.
Nest bound and nest-departed chicks crouch, hide, and run if threatened. If threat is direct, chicks will display by raising wings high and outstretched appearing larger while rocking from side to side similar to other owl species. If threat proceeds, chick leans backwards on wings and back, and thrust/attacks forward with legs and open feet, grabbing at threat with talons (Watson 1957, DWH).
Holt, Denver W., Matt D. Larson, Norman Smith, Dave L. Evans and David F. Parmalee. 2015. Snowy Owl (Bubo scandiacus), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA. https://doi.org/10.2173/bna.10