In flight the Gyrfalcon is fast and powerful, often appearing slower than it really is due to the size of the bird. Wingbeats are at times slow, deep and powerful, but on other occasions, wing movement is limited to the outer portions or "hands." Soaring and gliding on level wings as well as hovering have been noted. The level flight speed is faster than that of a Peregrine Falcon.
Hunting occurs near the ground with flight usually within six feet (1.9 meters) of the surface and following the contours of the land. This "contouring" behavior is often used in conjunction with some of the following major categories:
Perch and Wait
- a temporary perch such as a rock or low tree is used to spot potential prey before dropping off into a contouring flight pattern for the final approach.
Soaring and Quartering
- upon leaving a perch, birds may rise up at a steep angle and then circle or soar at heights of several hundred feet or more before moving away in search of prey. They rarely stoop from the soar as do Peregrine Falcons.
Contouring
- searching while flying low over the ground following the contours is an alternative to the soaring search.
Piracy- although normally shy, Gyrfalcons have followed trappers and hunters and taken prey that were flushed or killed. This behavior may occur with other birds but has not been documented.
Strike, Kill, and Consumption
- preferably from above and behind, a disabling blow with the feet is struck as the falcon approaches its prey at high speed. Upon a quick return, the victim is grasped with the talons and bitten through the neck at the base of the skull to effect the kill. More prey is taken on the ground or water than from the air. The prey may be eaten on the spot, but more often, it is taken to a plucking site where it is eaten or plucked and taken to the nest site. The sternum of large birds is bitten through and long bones pulled from their sockets as part of the feeding process.
The Gyrfalcon will bathe in both water and snow. Normally, the Gyrfalcon is thought of as a solitary bird that is usually seen alone or with a mate during the nesting season. The exception seems to be during the fall migration, or at certain high latitude wintering sites, where primarily juvenile birds will gather together. This may be in response to localized food resources and foraging opportunities as opposed to a desire for sociability. Nesting densities with internest distances as close as every 6 miles (9.6 kilometers) have been recorded in productive habitat in the Northwest Territories, but normally, distances are greater. The hunted areas of pairs in one Alaskan study ranged from 75 to 375 square miles (195 to 971 square kilometers) but this relates to food supply rather than defended territory.
There does not appear to be a pugnacious reputation surrounding this species as with some other falcons, but they are not fearful of attacking larger birds. Eagles seem particularly prone to their furious attacks if they have entered the breeding territory of a pair of falcons. The female Gyrfalcon is more inclined to make the attacks on these large birds, making them easily-trained by falconers to hunt larger species. In defense of its nest and territory, this large falcon will also attack wolverines, foxes, ravens, and other raptors, but it usually slips away at the sight of human beings. Quarreling with ravens in its territory is a frequent occurrence.
"Play" has been described primarily as mock attacks on inanimate objects and sometimes other birds. Young, captive falcons have attacked bushes, grass clumps, pieces of dirt, and other items during these activities.
Home ranges in Alaska vary from 83 to 700 square miles (215 to 1,813 square kilometers) and probably average closer to 400 square miles per pair (1,036 square kilometers). In Iceland, ranges as small as 25 square miles (65 square kilometers) were noted and in Sweden in a peak lemming year, single pairs may have been surviving within 1 square mile (2.6 square kilometers) ranges.
At certain latitudes, males occupy the breeding territory year round, presumably allowing them to defend the nest site and to establish it early in the process. The courtship phase includes variations and combinations of
several basic activities that include advertising by lone males, courtship flights by paired birds, nest ledge displays, food transfer and copulation. Advertising by the male includes at least the following activities with much variation on the core themes:
Eyrie Flyby
- this consists of repeated figure 8 flights past the nest with the crossing point directly in front of the nest. Wailing calls accompany the flight.
Wail-Pluck
- while plucking prey, the male will utter wailing calls, pause to look about and finally eat the item.
Male Ledge Display
- at a prospective nest site, the male will stand in a horizontal posture with the beak pointing downward and utter a series of "chup" notes. If mated, he may scrape the nest site.
Undulating Roll
- beginning in level flight, the male will partially roll in one direction and then roll 180 degrees in the opposite direction. Partway through the second roll, the bird will enter a steep dive and return to level flight at the bottom, rise again to the original altitude and begin the display again.
Wail
- wailing is a two syllable call given in a sequence of up to ten notes and is given more often by unmated males than by mated birds.
There are various flight behaviors where the female will join the male and execute a series of tandem activities such as mutual floating descent, passing and leading or food transfer. As well, a variety of pre-copulatory activities can be initiated by either sex. Copulation never seems to occur right at the nest site and begins about one month before egg laying. The number of copulation's for the entire nesting period is not likely as high as in other falcons and ends when the third egg is laid. Forty-seven copulation's were documented in one Yukon study.
Captive birds have lived as long as 30 years, but the average is closer to eight or 10 years. There appears to be no information recorded for wild birds. A high mortality for first year birds has been suggested by many authors, but information is presumptive and data is sparse. Starvation can affect nestlings when prey availability is lowered. On average, it appears that each pair of birds is able to raise two young and in good food years, this may increase to three. Sources of mortality include shooting, disease and starvation, with the latter likely being the greatest cause of death in most populations. Reduced production due to pesticide impacts does not seem to be a problem for Gyrfalcons. Predation by other raptors or mammals has been alleged but poorly documented. The impacts of illegal falconry are not documented for North America but this has been a cause of serious declines in Finland during this century. Elsewhere, heavy exploitation appeared to cause no decline.
ADAPTATIONS
The halux, or rear toe, is not fixed as in other falcons and can be rotated forward alongside the other three toes. This allows the bird to lie prone on the breast with both feet flat on the ground under the breast. Birds sleep in this position and can enter states of deep sleep. These circumstances are valuable during severe weather conditions when a lowered energy output and maximum heat retention position would be important survival aids. The clutch size appears to be directly linked to the size of the major prey populations. This is particularly useful to a species that has a limited prey base, and would be unable to feed a large clutch by simply increasing the variety of animals hunted to compensate for losses in other species.
