GYRFALCON

The Gyrfalcon, the largest of the Falcon species, is a bird of prey. The abbreviation Gyr is also used. It breeds on Arctic coasts, Tundra and the islands of northern North America and the Euro-Siberian region.

The Gyrfalcon is a very polymorphic species and therefore, its plumage varies greatly. The archetypal morphs are called "white", "silver", "brown" and "black", though they can be coloured on a spectrum from all-white to very dark. The brown 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 Gyrfalcon has a strongly black-spotted underside, rather than finely barred as in the peregrine. White Gyrfalcons are the only predominantly white falcons. Silver gyrfalcons resemble a light grey lanner falcon of larger size. The species shows no sex-based colour differences. The juveniles are darker and browner than adults.

The Gyrfalcon is a member of the Hierofalcon complex. In this group, ample evidence indicates hybridisation and incomplete lineage sorting which confounds analyses of DNA sequence data to a massive extent. The radiation of the entire living diversity of Hierofalcons took place around the Eemian Stage at the start of the Late Pleistocene. It represents lineages that expanded into the Holarctic and adapted to local conditions. This is in contrast to less northerly populations of north-eastern Africa (where the radiation probably originated) that evolved into the Sakerfalcon. Gyrfalcons hybridize not infrequently with Sakers in the Altai Mountains and this gene flow seems to be the origin of the Altaifalcon.