Description
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 1350 g (1.8 to 3 lbs) 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 64 in) wingspan, and of 1180 to 2100 g (2.6 to 4.6 lbs) weight. Among standard measurements, the wing chord is 34.5 to 41 cm (13.6 to 16 in), the tail is 19.5 to 29 cm (7.7 to 11 in), the culmen is 2 to 2.8 cm (0.79 to 1.1 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".
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Painting of a Greenland white morph (center), an intermediate (lower left) and black morph (back)
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A light silver-morph
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Male with a darker "silver" coloration
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Painting of brown morph adult (center) and juveniles
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