Last updated on April 18, 2014 at 16:58 EDT

Gyrfalcon, Falco rusticolus

The Gyrfalcon, also spelled as gerfalcon, is the largest of the falcon variety. This falcon breeds on Arctic coasts, and the islands of North America, Europe, and Asia. It mostly lives there as well, yet some Gyrfalcons disperse more widely after breeding season or in the winter. This bird is isolated throughout the Northern Hemisphere, with populations in Northern American, Greenland, and Northern Europe. The plumage varies with location, with birds being colored from all white, to dark brown. The Gyrfalcon is the national symbol of Iceland. For centuries, it has been a precious hunting bird, highly cherished among Vikings.

This bird’s common name comes from French gerfaucon, although in Medieval Latin gyrofalco. First part of the word may have come from Old High German gîr, meaning “vulture”, referring to its size related to other falcons, or from the Latin g?rus, meaning “circle” or “curved path” referring to its circling motion when catching prey. The male Gyrfalcon is called a gyrkin in falconry. The scientific name is composed up of the Latin term for a falcon, Falco, and for a country-side dweller, rusticolus.

The Gyrfalcon is very large; males are 48 to 61 cm (19 to 24 in) long. They weigh 1.8 to 3 pounds and have a wingspan from 43 to 51 in. Females are larger and bulkier, at 20 to 26 in long, 49 to 64 in wingspan, and weighing at 2.6 to 4.6 pounds. Amongst standard measurements, the wing chord is 13.6 to 16 in long, the tail is 7.7 to 11 in long, the culmen is .79 to 1.1 in, and the tarsus is 1.9 to 3.0 in.

This bird is a very polymorphic species, its plumage varying greatly. The standard colors are white, silver, brown, and black, although they can be colored on a spectrum that begins with all white and ends with very dark. The brown colored Gyrfalcon is distinguished from the Peregrine by the cream colored streak on the nape of the neck and crown and by the absence of the well defined malar stripe and cap. The black form of the falcon has a strongly black spotted underside, rather the fine bars of the Peregrine. The white forms of the birds are unmistakable as they are the only predominately white colored falcons. The silver gyrfalcons are look like a light grey Lanner Falcon of larger size. There is no difference in coloring between males and females, although the immature birds are darker and browner than the equivalent adults. The black color appears to be sex-linked and occurring in mostly females; it was difficult for breeders to get the males darker than the dark side of slate grey.

This Gyrofalcon is a component of the hierofalcon complex. In this cluster, there is liberal evidence for rampant hybridization and unfinished lineage sorting which perplex analysis of DNA sequence to an enormous extent. The radiation of the entire existing assortment of hierofalcons occurred in approximately the Eemian Stage at the start of the Late Pleistocene. It characterized lineages that stretched out into the Holarctic and adjusted to local conditions; this is in contrast to less northerly groups of northeastern Africa (where the radiation most likely came from) which turned into the Saker Falcon. Gyrfalcons hybridize frequently with the Saker Falcon in the Altai Mountains and this gene stream appears to be the derivation of the Altai Falcon.

There’s some association between locality and the color. Gyrfalcons in Greenland are lightest, with white feathers dotted with grey on the back and wings being most widespread. Other subpopulations have changeable quantities of the darker morphs; the Icelandic lean towards pale, where as the Eurasian populations are significantly darker and normally have no white birds. Ordinary separation into regional subspecies is prohibited by the Gyrfalcons habit of flying long expanses while exchanging alleles among subpopulations; as a result, the allele distributions for the color polymorphism produce clines and in darker birds of unknown origin, theoretically any allele arrangement might be present. For example, a mating of a couple of captive Gyrfalcons is documented to have made a clutch of four young; a white, a silver, a black, and a brown.

As a general rule, geographic discrepancy follows Bergmann’s Rule for size and the need of crypsis for plumage coloration. More than a couple subspecies have been named in relation to distinguishable differences in populations but none of these are unfailing and so no living subspecies are accepted today. Conceivably the Icelandic population described as Falco rusticolus islandus is the most dissimilar. The primarily white Arctic forms are parapatric and flawlessly fall into the subarctic populations, where as the birds of Iceland have supposedly less gene flow with their neighbors and surely show fewer differences in feather colors and most often look quite similar to a large, washed-out Peregrine Falcon.

A recently conducted molecular study, however, recognized the Icelandic population as genetically unique compared to other sampled populations in eastern and western Greenland, Canada, Alaska, and Norway. Within Greenland, differing levels of gene flow between eastern and western sampling locations was identified with obvious asymmetric dispersal in western Greenland from north to south.   This dispersal predisposition in is agreement with the distribution of plumage color differences with white Gyrfalcons in much larger quantity in northern Greenland. Further work is needed to find out the ecological factors adding to these distributions relative to feather coloring differences, and whether renewed subspecies descriptions are needed.

A paleosubspecies, Falco rusticolus swarthi, lived during the Late Pleistocene (125,000to 13,000 years ago). Fossils unearthed in Little Box Elder Cave in Converse County, Wyoming, Dark Canyon Cave in Eddy County, New Mexico, and in McKittrick, California were firstly described as Falco swarthi (“Swarth Falcon” or more properly “Swarth’s Gyrfalcon”) because of their distinctive size. They have meanwhile demonstrated to be fundamentally undividable from those of living Gyrfalcons, except for being rather larger.
Swarth’s Gyrfalcon is on the higher end of the present Gyrfalcons size range, strong females even surpassing it. It appears to have adjusted to the temperate semiarid climate that dominated in its range during the last ice age. Ecologically more like the Siberian populations of today (which are usually composed of smaller birds) or to the Prairie Falcon, this population of moderate steppe habitat must have hunted land birds and mammals rather than in the water and on the seabirds which compose of much of the American Gyrfalcons diet today.

Originally thought of to be a bird of tundra and mountains only, the Gyrfalcons were revealed in June 2011 to spend sizeable periods during the winter on sea ice far from land. It feeds on birds and mammals only, the latter of which it takes more regularly than many other falco species. Like other hierofalcons, it usually hunts in a straight quest rather than the speedy stoop from a height like the peregrine. Most of their prey is killed on the ground, whether the bird catches it there or if the victim is flying bird, forced to the ground. The diet is to some degree opportunistic, but a majority of breeding birds rely on lagopus grouse and avian marine species on coastal habitats. Avian prey can differ in size from redpolls to geese and can insist of gulls, corvids, smaller passerines, waders and other raptors. Mammalian prey can vary in size from shrews to marmots (sometimes three times the weight of the assaulting falcons) and usually consists of lemmings, voles, ground squirrels, and hares. They aren’t usually observed eating carrion.

The falcons almost always nest on cliff faces. Falcon pairs do not build their own nests, but use bare cliff faces or the abandoned nests of other birds, mostly Golden Eagles or Common Ravens. Although the clutch can range from 1 to 5 eggs, there are normally only 2 to 4. The average size of the eggs are 2.31×1.8 in; the average weight being 2.2 oz. Incubation period averages at about 35 days, with the hatchlings (chicks) weighting about 1.8 oz. The nestlings are brooded for 10 to 15 days and then leave the nest at 7 to 8 weeks. When they are 3 to 4 months old, the immature falcons become independent from their parents, though they may still correlate with their siblings through the following winter.

The only natural marauder of the Gyrfalcons are Golden Eagles and even they rarely engage with these fearsome falcons. These falcons have been known to become aggressive towards animals that come near their nests, although the Common Raven are the only predators known to successfully pick off Gyrfalcons eggs and hatchlings. Brown bears have even been supposedly dive-bombed. Humans, whether accidentally or intentionally, are the primary cause of death for the Gyrfalcons. Gyrfalcons that survive, can live up to 20 years of age. Because this species has such a wide range, it is not considered threatened by the IUCN. It is not much influenced by habitat devastation, but pollution. For example, pesticides, decreased its numbers in the mid 20th century, and until 1994 it was said to be “near threatened”. Improving environmental values in well to do countries have let the birds make a comeback, and so today they are not measured to be rare or endangered.

These birds have had prolonged association with humans, who have found them to be primarily useful for hunting and the art of falconry. Today it is the official bird of Canada’s Northwest territories. The white falcon on the crest of the Icelandic Republics coat of arms is an assortment or Gyrfalcons.

The Gyrfalcon was thought of as a royal bird in the Medieval Era. Geographer and Historian, Ibn Said al-Maghribi, portrayed specific northern Atlantic islands west of Ireland where these falcons would be brought from, and how the Egyptian Sultan paid 1,000 dinars (official currency) for each Gyrfalcon (or if it arrived dead, 500 dinars). Because of its rarity and how difficult it was to obtain it, in European falconry, they were reserved for Kings and Nobles; very seldom would you see a man of lesser rank with a Gyrfalcon on his fist.

In 12th century AD China, hunting swans with Gyrfalcons acquired from the Jurchen tribes became fashionable amongst the Khitan nobility. When the demand for these birds surpassed the supply, the Liao Emperor enforced a tax payment-in-kind of Gyrfalcons on the Jurchen; under the last Liao emperor, tax collectors were permitted to use force to attain sufficient Gyrfalcons. This was only one cause of the Jurchen rebellion, whose leader Wanyan Aguda eradicated the Liao Empire in 1125, and acclaimed the Jin Dynasty in its stead.

To this day, Gyrfalcons are expensive to buy, so owners and breeders may perhaps keep them secret to avoid theft. The birds can and they frequently do fly long expanses, and falconers may mount a radio-tracker to assist in recovery. Wild Gyrfalcons are not really exposed to disease, and as a result have immune systems that are untested to many avian pathogens found around human environments. Therefore, many gyrfalcons that are taken from the wild quickly die of disease.

Falcons are renowned to be very prone to avian influenza. For that reason an experiment was done with hybrid gyr-saker falcons, which found that 5 falcons immunized with a commercial H5N2 influenza vaccine survived infection with a highly pathogenic H5N1 strain, where as 5 falcons that were not vaccinated died. Because both wild and captive Gyrfalcons are valuable for not only falconry but for wildlife conservation as well, this means they can be protected from bird flu by vaccination.

Image Caption: Fálki (Falco rusticolus) – Gyr Falcon. Credit: Ólafur Larsen/Wikipedia (CC BY-SA 2.0)

Gyrfalcon Falco rusticolus