Gyrfalcon

Falco rusticolus

Description 4

The gyrfalcon is a very large falcon, being about the same size as the largest buteos (buzzard hawks). Males are 48 to 61 cm (19 to 24 in) long, weigh 805 to 1,350 g (1.775 to 2.976 lb) and have a wingspan from 110 to 130 cm (43 to 51 in). Females are bulkier and larger, at 51 to 65 cm (20 to 26 in) long, 124 to 160 cm (49 to 63 in) wingspan, and of 1,180 to 2,100 g (2.60 to 4.63 lb) weight. Among standard measurements, the wing chord is 34.5 to 41 cm (13.6 to 16.1 in), the tail is 19.5 to 29 cm (7.7 to 11.4 in), the culmen is 2 to 2.8 cm (0.79 to 1.10 in) and the tarsus is 4.9 to 7.5 cm (1.9 to 3.0 in). The gyrfalcon is larger than the peregrine falcon, which it is known to hunt, and differs from the buzzard in general structure, being unmistakably a falcon with pointed wings, and broader-winged and longer-tailed than the peregrine.

The gyrfalcon is a very polymorphic species, so its plumage varies greatly. The archetypal morphs are called "white", "silver", "brown", and "black", though they can be coloured on a spectrum that begins with all-white and ends with very dark. The brown form of the gyrfalcon is distinguished from the peregrine by the cream streaking on the nape and crown and by the absence of a well-defined malar stripe and cap. The black morph has its underside strongly spotted black, rather than finely barred as in the peregrine. White form gyrfalcons are unmistakable, as they are the only predominantly white falcons. Silver gyrfalcons resemble a light grey lanner falcon of larger size. There is no difference in colouring between males and females; and juveniles are darker and browner than the corresponding adults.

The black color seems to be sex-linked and to occur mostly in females; it proved difficult for breeders to get males darker than the dark side of slate grey. A color variety that arose in captive breeding is "black chick".

Painting of a Greenland white morph (center), an intermediate (lower left), and black morph (back)

Light silver-morph

Male with a darker "silver" coloration

Painting of brown morph adult (center) and juveniles

Ecology 4

The gyrfalcon was originally thought to be a bird of tundra and mountains only; however, in June 2011 it was revealed that it spends considerable periods during the winter on sea ice far from land. It feeds only on birds and mammals, the latter of which it takes more regularly than many other Falco species. Like other hierofalcons, it usually hunts in a horizontal pursuit, rather than with the peregrine's speedy stoop from a height. Most prey is killed on the ground, whether they are captured there or, if the victim is a flying bird, forced to the ground. The diet is to some extent opportunistic, but a majority of breeding birds mostly rely on Lagopusgrouse and avian marine species on coastal habitats. Avian prey can range in size from redpolls to geese and can include gulls, corvids, smaller passerines, waders, and other raptors (up to the size of Buteos). Mammalian prey can range in size from shrews to marmots (sometimes thrice the weight of the assaulting falcon), and often includes lemmings, voles, ground squirrels, hares and rarely also bats. They are rarely observed eating carrion.

Sources and Credits

  1. (c) Bill Gracey, some rights reserved (CC BY-NC-ND), https://www.flickr.com/photos/9422878@N08/15997983503/
  2. (c) Urville Djasim, some rights reserved (CC BY-ND), https://www.flickr.com/photos/urville_djasim/3424879804/
  3. (c) soluslupus13, some rights reserved (CC BY-SA), https://www.flickr.com/photos/kingnaturephotos/17334588015/
  4. (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Gyrfalcon

More Info

Range Map

iNatCA Map

Color grey, white
Animal Bird
Bird Falconidae (falcons hobbys kestrels & merlin)