Behavior

Locomotion

Walking, Hopping, Climbing, Etc.

More at ease on ground than most falcons. Walks on ground or nest ledge with body held horizontally (to prevent stiff tail from dragging) and slight side-to-side rocking (owing to relatively wide body). Relatively quick, agile runner, for a falcon. Will run on ground to pursue prey or on nest ledge to displace another bird. Will hop onto rocks and other objects to perch, with aid of wings. Can climb some surfaces with aid of wings (most commonly seen in young birds), but more likely to hop or fly.

Flight

See descriptions under Distinguishing Characteristics and Food Habits: feeding, food capture and consumption; and under Sexual Behavior. Generally more buoyant and less maneuverable than Peregrine Falcon, but faster in and more capable of sustained flight. Little quantification of flight. Quartering flight at 1–18 m above ground, soaring at 60–900 m (White and Weeden 1966, Platt 1977, Jenkins 1982, White and Nelson 1991). A soaring male flew a minimum of 44 km in about 67 min, giving a minimum speed of 40 km/h (White and Nelson 1991). Trained falcons flying 500 m to a lure demonstrated average minimum power speeds of 11.4 m/s, relative air speed of 1.53, and wing beat frequencies of 5.27 HZ (Pennycuick et al. 1994). This latter study suggests that in “chase mode” additional power is gained by reducing wingspan (sacrificing the efficiency associated with constant circulation of air around the wing) and increasing wing beat frequency. Temporary disregard for fuel efficiency combined with a substantial aerobic scope enable the slower-flying Gyrfalcon to chase down its faster-flying prey. When stooping, a captive male Gyrfalcon reached a maximum speed of 209 km/h (Tucker et al. 1998). The bird’s stoop consisted of three phases: 1) acceleration phase during which the bird dove at 17-62° from horizontal accelerating with minimum drag, 2) brief constant-speed phase when the bird increased drag to maintain speed, and 3) deceleration phase when the bird increased drag dramatically by cupping its wings in a high angle of attack before grabbing a swinging lure. Theoretically, Gyrfalcons in the wild could reach speeds of 250 km/h or more on very long stoops (Tucker et al. 1998).

Self-Maintenance

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

Not reported in detail. Preens frequently, using uropygial gland. Generally rouses (shakes) after preening, and will rouse during flight. Middle toe used to scratch (directly), mostly around cere and head. Stretches by laterally extending wing and leg on same side, and by bowing body forward and extending both wings up and forward with upper surfaces facing each other. Bathing consists of rocking body back and forth, dipping head in water, and fluttering wings and tail while holding feathers erect and away from body. Bathing in wild birds does not appear to differ from behavior of captive birds. One bathing bout observed in Greenland lasted 17 min (Jenkins 1982). Birds bathe in pools of runoff water on still-frozen rivers, in pools on tundra, and at edges of flowing rivers (Platt 1977, TJC). Platt (1977) twice observed a male dustbathe, using same site at same time of day. Dustbathing occurred on sunny days with temperatures near 5°C on a south-facing slope. Both sexes observed dustbathing repeatedly over the course of a breeding season in a small gravel opening on a south-facing slope (TLB). Birds scooted down the 3-m gravel slide while exhibiting bathing motions described above. Captive birds have also been observed to bathe in snow (B. Walton pers. comm.).

Sleeping, Roosting, Sunbathing

Sunbathing not documented in wild but has been observed in captivity. Sleeps with head tucked in back or scapular feathers, in normal perching position with head facing forward but hunkered slightly, or lying down in incubating position, sometimes with head on scrape. Sleeping with head under scapulars tends to occur mostly at “night” and is associated with longest sleep periods. During brooding, female sleeps 28% of time, or over 6h/d (Jenkins 1982). Little information on roosting. During breeding season, probably roosts near nest site; female does not spend “night” on nest ledge after brooding ceases. Male does not roost at nest ledge. Young roost together after fledging (Fletcher and Webby 1977). Presence of fresh mutes, prey remains, pellets, tracks in snow, plus occasional sightings and molted down and feathers, indicate that most nest sites are used for roosting during winter (Cade 1960, Platt 1977, Nielsen 1986, Poole and Bromley 1988b). In nonbreeding areas, wild birds will roost on ground (G. H. Sanchez pers. comm.) as will trained birds left out at night (TJC). Trained birds also observed roosting in Raven’s nest (B. Walton pers. comm.).

Daily Time Budget

Not well quantified. Shortly before egg-laying, female spends most of time sleeping on nest ledge (Platt 1977). For time spent incubating and brooding, see Breeding: incubation, and parental care. By 2–4 wk posthatching, both parents are largely absent from nest site except to deliver food (Fletcher and Webby 1977, Jenkins 1978). Seasonal differences in time budget expected owing to extreme differences in day length between breeding and wintering seasons.

Agonistic Behavior

Physical Interactions

Both sexes will chase and strike at intra- and interspecific intruders during breeding (Cade 1960, Platt 1977, Nielsen and Cade 1990b) and nonbreeding seasons (Sanchez 1993). Gyrfalcons are believed to have killed intruding Common Ravens, Rough-legged Hawks (Buteo lagopus), and Peregrine Falcons (see Cade 1960). Gyrfalcon will also flee, at least from Peregrine Falcon, if former is intruder (Cade 1960). In aerial combat Gyrfalcon sometimes locks talons with intruder; the birds cartwheel down through air and may strike the ground bound together (TJC).

Communicative Interactions

Threat Displays. Involve a combination of behaviors, depending on intensity: facing toward source of threat, gaping, erecting feathers, head held along body axis, and hissing. Least intense form is Upright Threat. In its mildest form, bird pulls itself upright with beak toward threat, wings closed, feathers sleeked except for flared cheek feathers, and gapes briefly. In captivity, often used when a bird lands on a perch near its mate. More exaggerated form of Upright Threat, typically seen in young birds, is for bird to pull itself upright with beak toward threat, spreading wings to sides and flaring all feathers, including tail, gape (protracted), hiss, and if pressed, fall backward, to defend itself with feet. Most intense form is Horizontal Threat, in which bird orients its body horizontally, flares feathers of back, crown, and cheeks, and points its beak toward threat. Unlike Upright Threat, which is largely defensive, Horizontal Threat places bird in a position ready for attack. Threat displays observed in both wild and captive birds, but are relatively infrequent compared to Peregrine Falcon.

Appeasement Displays. Appeasement or submissive displays involve behaviors that are generally direct opposites of threat displays: turning beak away, sleeking feathers, holding head below body axis (often pointed down), silent or giving soft, chick-like call. Most typically seen during breeding; see below, Sexual Behavior: pair bond (NJC, TJC).

Spacing

Territoriality

Nature and extent of territory. Territories centered on nest cliffs, usually regularly spaced (Poole and Bromley 1988b). Mean internest distances range between 5 and 96.7 km; distances related to nest-site availability and habitat productivity and vary geographically and annually (Cade 1960, Burnham and Mattox 1984, Nielsen 1986, Mossop and Hayes 1994, Shank and Poole 1994). Actual area most often defended is a horizontal oval < 1,400 m long (centered on nest ledge) and 400–500 m deep (Platt 1977).

Manner of establishing and maintaining territory. Little information on establishment of territories. In Yukon, an unpaired male occupying a nest site early in breeding season daily gave 4 different advertisement displays (Platt 1977). Eyrie-flyby Display consists of male flying (horizontally) parallel to cliff face in a figure eight about 10 m from eyrie, with crossing point in front of eyrie. Repeated 2–3 times, accompanied by Wail; prey often carried. Wail-pluck Display occurs when male returns with prey, or occasionally when discarded prey is recovered from perch. Male begins to Wail and slowly plucks prey, pausing to look around but continuing to Wail. In this way, male takes twice the normal time to pluck and eat a ptarmigan. Two other displays, Male Ledge and Undulating Roll, also performed by paired males (see Sexual Behavior: pair bond). Wail vocalization more prevalent in unpaired males.

Territories maintained by aggressive vocalization (Kak) and pursuit of intruders. Few documented intraspecific interactions (1 each: Jenkins 1978, Platt 1977, 1989, Woodin 1980). Higher frequency of intraspecific interactions (n = 10) in Iceland may be related to higher density (mean internest distance 6.2–8.1 km, Nielsen 1986). Likewise, in w. Alaska with internest distances similar to Iceland, 4 intraspecific interactions near nests observed in one year, all were resident pairs pursuing intruding sub-adults (TLB). Resident females respond similarly to all intruders; resident males show relatively little aggression toward intruding females, but repeatedly attack and chase (up to 1 km) intruding males (Nielsen and Cade 1990b).

Interspecific territoriality. Interspecific interactions involve other predatory birds, i.e., Common Raven, Rough-legged Hawk, Golden Eagle, Red-tailed Hawk (Buteo jamaicensis), Northern Harrier (Circus cyaneus), Snowy Owl (Nyctea scandiaca) (Evans 2000), and Peregrine Falcon. Attacks documented on a red fox (Vulpes vulpes) and a wolverine (Gulo gulo) near nest cliff, although a passing timber wolf (Canis lupus), porcupine (Erethizon dorsatum), grizzly bear (Ursus arctos), and caribou (Rangifer tarandus) elicited no response (Platt 1977). Vocalization (Kak) and behavior (pursuit/attack) similar to that directed at conspecifics. Level of aggression influenced by proximity, behavior of intruder, and individuality of falcons. Some pairs will not tolerate presence of predatory birds, attacking them whenever opportunities arise, especially Golden Eagles, whereas others will tolerate nesting on same cliff if intruders do not fly toward nest (Cade 1960, Platt 1977, Poole and Bromley 1988a, Nielsen and Cade 1990b).

Winter territoriality. No information on territoriality of birds wintering at nest sites. Birds wintering outside breeding area aggressively pursue conspecifics and other predatory birds (Dobler 1989, Sanchez 1993). Behavior toward other species is similar to that seen during breeding season. Roughly half of interspecific interactions observed in South Dakota involved food defense. Behavior toward conspecifics differs from that during breeding season; instead of “resident” driving “intruder” away, the 2 birds alternate pursuit of each other, suggesting this behavior represents defense of individual space rather than territory defense (Sanchez 1993).

Dominance hierarchies. Not known to occur, but females believed dominant over males (Cade 1982), and adults may displace immatures (Sanchez 1993).

Individual Distance

Pairs and nest-mates will sit side by side. Once brooding ceases, adults generally perch within 100 m of nest ledge, except when delivering food (Platt 1977). Independent birds defend individual space (see Demography and Populations: range) throughout annual cycle (Sanchez 1993).

Sexual Behavior

Mating System And Sex Ratio

Monogamous. No information on primary sex ratio. Sex ratio of nestlings 1:1 (Poole and Bromley 1988b, Cade et al. 1998).

Pair Bond: Courtship Displays And Mate-Guarding

Descriptions of wild birds from Platt (1977) unless otherwise noted. Descriptions of captive birds from Platt (1977) and Wrege and Cade (1977). Descriptions presented in order of occurrence. For descriptions of vocalizations and contextual differences between wild and captive birds, see Vocalizations.

Displays at the nest ledge. A Visit consists of falcon standing alone in normal perching posture, or walking into eyrie and standing upright. Performed by either sex, lasting 1–21 min; not described in captive birds as separate display. No vocalization accompanies this activity. Vertical Head-low Bow given with body in normal perching position, feathers sleeked, and head depressed and oriented away from mate; given by either sex. Horizontal Head-low Bow is more intense form, given with body held horizontally, feathers sleeked, and head bent at almost 90° to body and oriented away from mate; given by either sex. In captivity, head may be bobbed or held stationary; vigorous bowing of Peregrine Falcon not seen. Head-low Bows occur as isolated displays in captive birds, but are not described outside context of Ledge Displays and Food Transfers in wild birds. In captivity, both Vertical and Horizontal Head-low Bows are much more discrete, less intense, and used less frequently than in Peregrine Falcon. Males use these displays more frequently than females in both species. Scraping is done by either sex and consists of bird leaning forward, rocking from side to side, placing its weight on its breast with tail relaxed, and pushing vigorously backward with feet to form a small depression. After Scraping several times, bird may turn to face a different direction and continue Scraping. No vocalization accompanies this activity. Occurs as solitary activity or as part of Individual Ledge Display. Male Ledge Displays consist of male approaching scrape in Horizontal Head-low Bow position with high steps (causing body to rock back and forth), giving Chup vocalization. Male pauses to look at female, whose reaction determines intensity and duration of display. Female Ledge Displays similar to those of male, but female does not tend to pause to look at male, displays are less intense, less frequent, and occur later in season. Mutual Ledge Displays occur when female approaches scrape during Male Ledge Display. Unlike Peregrine Falcons, Gyrfalcons remain stationary during display and rarely pause. Male generally terminates display by leaving scrape while female remains. Billing consists of female turning head sideways, orienting beak up while male’s is directed downward; birds nibble between beaks. In captive birds, Billing occurs during Mutual Ledge Displays and when birds are perched closely together. Vocalizations tend to degrade during Billing. Not observed in wild birds. Scraping, Male Ledge Displays, Female Ledge Displays, and Mutual Ledge Displays are essentially identical between captive and wild birds (but see Vocalizations for differences in accompanying vocalizations).

Aerial displays. Five aerial displays described in wild birds, occurring mostly within egg-laying period. Roll is executed by male while in long dives, at angles between 30 and 60°. A partial roll of 20° precedes a roll of 180° in opposite direction. Male remains with dorsal surface down for 1–2 s, then roll is reversed and dive continues in normal flight position. In Undulating Roll, male begins a brief glide with extended wings from level flight at moderate speed; body then briefly rotates laterally about 20°, then rotates 180° in opposite direction. When second rotation is half completed, male begins a steep dive, becoming vertical with ventral surface facing in original direction of flight. This position is held as male dives 30–50 m, then he returns to normal flight position by rotating in opposite direction from 180° roll. At this point, dive is terminated and bird is carried upward at steep angle. When original elevation is reached, maneuver is repeated. This display may be modified by eliminating 20° roll at beginning of second dive, or by pitching over backward into an inside loop. Males also Flash by rolling laterally 90° to one side and then the other during flight, producing a flashing or flickering effect as dark back and light breast are alternately exposed (TJC). In Mutual Floating Display, male positions himself 2–3 m above soaring female, and both birds drop slowly at about 20° angle. Both birds hold wings partially closed and slightly above back with legs extended and tails spread. Display lasts 10–13 s, male gives Kak vocalization; constant distance between pair is maintained. In Passing and Leading Display, male overtakes flying female, passing close by, and begins weaving back and forth in front of her. Aerial displays do not occur in captive birds.

Food transfers. Food Transfers begin about 10 d prior to egg-laying and continue through nestling period. In wild birds, all transfers are from male to female and always involved a freshly killed prey item. About 85% of Food Transfers in wild birds occur on perches. Male approaches nest site with prey in feet, giving Wail vocalization. As he perches, he changes to Chup vocalization. Female then crouches with body feathers puffed out and wings partially extended. Female flies to male in a Flutter-glide (also called Sandpiper Flight, Cade 1960), with shallow wing beats, tail slightly fanned and pointing downward, with a Beg call. Male picks up food in beak and presents it in Vertical Head-low Bow posture, female lands next to male approaching in a slightly aggressive horizontal posture and takes food in foot or beak in a Horizontal Head-low Bow posture. In captivity, female-male transfers occur, though less frequently than male-female transfers. Captive birds also use cached items or scraps in transfers. Captive females do not beg from males. In both captive and wild birds, female typically goes to male if transferring outside of nest, otherwise wild male may deliver directly to brooding female (TLB). Aerial Food Transfers occur prior to egg-laying and after brooding, when female is able to detect approaching male before he lands. As female watches male approach, she makes flight intention movements, then flies towards him in a Flutter-glide, reaching him as far as 400 m from cliff. Female flies about 10 m above male, climbs slightly, dives in front, and pitches up underneath him, turning upside down to grab prey. Male appears to adjust speed, sometimes almost hovering. No aerial transfers in captive birds.

Copulation; Pre- And Postcopulatory Displays

Either sex can solicit copulation; display by either sex generally induces other sex to display. Males use Curved Neck Display: standing erect while arching neck and pointing beak down and away from female so that back of neck is highest part of bird; no vocalization given. In captivity, this display accompanied by a Chitter, and when female is very close, male may assume Vertical Head-low Bow position or turn perpendicular to her. Females generally respond to Curved Neck Display with Copulation Solicitation, in which female assumes a horizontal position with head below plane of body, beak pointing down, and tail raised slightly above back; a soft Whine is given. In captivity, females appear to be more aggressive in this posture, often approaching male head-on (see above, Agonistic Behavior: communicative interactions, threat displays). As male approaches for copulation, female’s Whine changes to Chitter and her body tilts forward to about 45°. Male hovers briefly about 50 cm above female, orients to face same direction as female, and lands on her back in a vertical Curved Neck position, supported on his tarsi between female’s humeri and thorax, with toes contracted and feet turned inward. Male’s wings constantly flap and tail points straight down and shuffles from side to side. Male gives Chitter vocalization. Female’s wings are slightly opened and tail is vertical and slightly to side. Female’s Whine becomes a copulatory Wail. In wild, copulation can occur up to 29 d prior to egg-laying and continues through egg-laying; each copulation lasts 4–12 s, during which male makes 4–5 thrusts. In captivity, young males attempt to climb rather than fly onto female’s back (Wrege and Cade 1977). Observations on captive birds at high latitude also indicate that copulations are more frequent during warm weather and immediately before egg-laying (Seifert 1982).

Duration And Maintenance Of Pair Bond

Within a breeding season, all pairs remain together at least until young have dispersed. Roughly half of territories occupied during nonbreeding season had pairs (Platt 1977, Nielsen and Cade 1990b), which had presumably remained together year-round. No information on longevity of pair bond; presumably birds remain mated until one dies, then readily re-pair.

Extra-Pair Copulations

Not known to occur. A female-female pairing of a Gyrfalcon and Peregrine Falcon that laid eggs in and shared incubation duties on a nest was documented in 1989 and 1990 in Norway (Gjershaug et al. 1998); no eggs hatched.

Social And Interspecific Behavior

Degree Of Sociality

Solitary or in pairs during breeding and nonbreeding season (Platt 1977, Nielsen and Cade 1990b). Fledglings may roost together (Fletcher and Webby 1977). Small groups (6–8) of immatures sometimes seen in fall (Cade 1982).

Play

Similar to Peregrine Falcon. Immature birds will attack inanimate objects and make abortive attacks on live animals with no apparent attempt to kill (Cade 1953). Unlike Peregrine Falcons, trained adult Gyrfalcons remain playful (TJC).

Interactions With Members Of Other Species

Mobbed by small diurnal passerines. Wintering Gyrfalcons were robbed of prey by Bald Eagle (Haliaeetus leucocephalus) (Dekker and Court 2003); 1 record of attempted robbery by conspecific (Jenkins 1978). Commensal nesting in North America: Canada Goose (Branta canadensis) within 2.5 and 4.5 m, Common Eider (Somateria mollissima) and White-fronted Goose (Anser albifrons) within 36 m, Green-winged Teal (Anas carolinensis) within 180 m, all unmolested (White and Springer 1965, K. Poole pers. comm.).

Predation

Two yearling falcons (males) found as food remains in 2 different Common Raven nests, probably picked up as carrion (Nielsen and Cade 1990b). Remains of juvenile Gyrfalcon found in two pellets removed from a Gyrfalcon nest (Booms and Fuller 2003a). Golden Eagle is potential, but not documented, predator of wild Gyrfalcons, as demonstrated by degree of aggression and caution accorded them (Platt 1977). Trained Gyrfalcons often killed by Golden Eagles on quarry or in flight (TJC). C. M. White (pers. comm.) saw a flying adult Gyrfalcon struck by a female Peregrine in the Aleutians, breaking the Gyrfalcon’s wing. The Gyrfalcon was subsequently caught and killed by a Bald Eagle.