Gyrfalcon

Gyrfalcon or Gerfalcon
Conservation status

Least Concern (IUCN 3.1)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Subclass: Neornithes
Infraclass: Neognathae
Superorder: Neoaves
Order: Falconiformes
Family: Falconidae
Genus: Falco
Subgenus: (Hierofalco)
Species: F. rusticolus
Binomial name
Falco rusticolus
Linnaeus, 1758

The Gyrfalcon (pronounced /ˈdʒɜrfɔːlkən/ or /ˈdʒɜrfælkən/; also spelled gerfalcon) Falco rusticolus is the largest of the falcon species. The Gyrfalcon breeds on Arctic coasts and the islands of North America, Europe, and Asia. It is mainly resident there also, but some Gyrfalcons disperse more widely after the breeding season, or in winter.[nb 1] The Gyrfalcon is dispersed throughout much of the Northern Hemisphere, with populations in Northern America, Greenland, and Northern Europe. Its plumage varies with location, with birds being coloured from all-white to dark brown.

The bird's common name comes from French gerfaucon; in medieval Latin it is gyrofalco. The first part of the word may come from Old High German gîr (cf. modern German Geier) for "vulture", referring to its size compared to other falcons; or from the Latin gȳrus for "circle" or "curved path"—from the species' circling as it searches for prey, distinct from the hunting of other falcons in its range.[nb 2] The male Gyrfalcon is called a gyrkin in falconry. The scientific name is composed of the Latin term for a falcon, Falco, and for a countryside-dweller, rusticolus.

Contents

Description

This species is a very large falcon, being about the same size as the largest buteos. 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. The Gyrfalcon is in size between the Peregrine Falcon and the hawk in general structure, being unmistakably falcons with pointed wings, but also being 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 birds and ends with very dark ones. 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 birds resemble a light, grey Lanner Falcon of larger size. There is no difference in colouring between males and females; and juveniles gyrkins are darker and browner than the corresponding adults.

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

A light silver-morph

Male with a darker "silver" coloration

Painting of brown morph adult (center) and juveniles

Systematics and evolution

A hybrid White Gyrfalcon × Saker hybrid

The Gyrfalcon is a member of the hierofalcon complex. In this group, there is ample evidence for rampant 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 in approximately 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 northeastern Africa (where the radiation probably originated) which evolved into the Saker Falcon. Gyrfalcons hybridize not infrequently with Sakers in the Altai Mountains and this gene flow seems to be the origin of the Altai Falcon.[1]

There is some correlation between locality and colour morph. Greenland Gyrfalcons are lightest, with white plumage flecked with grey on the back and wings being most common. Other subpopulations have varying amounts of the darker morphs: the Icelandic birds tend towards pale, whereas the Eurasian populations are considerably darker and typically incorporate no white birds. Natural separation into regional subspecies is prevented by Gyrfalcons' habit of flying long distances whilst exchanging alleles between subpopulations; thus, the allele distributions for the color polymorphism form clines and in darker birds[nb 3] of unknown origin, theoretically any allele combination might be present. For instance, a mating of a pair of captive Gyrfalcons is documented to have produced a clutch of 4 young: one white, one silver, one brown, and one black.

Adult F. r. islandus at Dimmuborgir near Lake Myvatn (Iceland)

In general, geographic variation follows Bergmann's Rule for size and the demands of crypsis for plumage coloration. Several subspecies have been named according to perceived differences between populations[nb 4] but none of these are consistent and thus no living subspecies are accepted today. Perhaps the Icelandic population described as Falco rusticolus islandus is the most distinct. The predominantly white Arctic forms are parapatric and seamlessly grade into the subarctic populations, whereas the birds of Iceland have presumably less gene flow with their neighbors and indeed show less variation in plumage colors and often look quite similar to a large, washed-out Peregrine Falcon (although their habitus is different). Comprehensive phylogeographic studies to determine the proper status of the Icelandic population have yet to be determined.[2]

A recent molecular study,[3] however, identified the Iceland population as genetically unique relative to other sampled populations in both eastern and western Greenland, Canada, Alaska and Norway. Further, within Greenland, differing levels of gene flow between western and eastern sampling locations was identified with apparent asymmetric dispersal in western Greenland from north to south. This dispersal bias is in agreement with the distribution of plumage colour variants with white Gyrfalcons in much higher proportion in northern Greenland.[3] Further work is required to determine the ecological factors contributing to these distributions relative to plumage differences, and whether renewed subspecies designations are warranted.

A paleosubspecies, Falco rusticolus swarthi, existed during the Late Pleistocene (125,000 to 13,000 years ago). Fossils found in Little Box Elder Cave (Converse County, Wyoming), Dark Canyon Cave (Eddy County, New Mexico), and McKittrick, California were initially described as Falco swarthi ("Swarth Falcon" or more properly "Swarth's Gyrfalcon") on account of their distinct size. They have meanwhile proven to be largely inseparable from those of living Gyrfalcons, except for being somewhat larger.[4]

Swarth's Gyrfalcon was on the upper end of the present Gyrfalcon's size range, strong females even surpassing it (Miller 1935). It seems to have had some adaptations to the temperate semiarid climate that predominated in its range during the last ice age. Ecologically more similar to the Siberian populations of today (which are generally composed of smaller birds) or to the Prairie Falcon, this population of temperate steppe habitat must have preyed on landbirds and mammals rather than the water—and on the seabirds which make up much of the American Gyrfalcon's diet today.

Ecology

The Gyrfalcon is a bird of tundra and mountains, with cliffs or a few patches of trees. It feeds only on birds and mammals. 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 Lagopus grouse 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 include lemmings, voles, ground squirrels, and hares. They are rarely observed eating carrion.

Breeding

A chick hatched in captivity

The Gyrfalcon almost invariably nests on cliff faces. Breeding pairs do not build their own nests, and often use a bare cliff ledge or the abandoned nest of other birds, particularly Golden Eagles and Common Ravens. The clutch can range from 1 to 5 eggs, but is usually 2 to 4. The average size of an egg is 58.46 x 45 mm (2.31 x 1.8 in); the average weight is 62 g (2.2 oz). The incubation period averages 35 days, with the chicks hatching at a weight of around 52 g (1.8 oz). The nestlings are brooded usually for 10 to 15 days and leave the nest at 7 to 8 weeks. At 3 to 4 months of age, the immatures become independent of their parents, though they may associate with their siblings through the following winter.

The only natural predator of Gyrfalcons are Golden Eagles and even they rarely engage with these formidable falcons. Gyrfalcons have been recorded as aggressively harassing animals that come near their nests, although Common Ravens are the only predators known to successful pick off Gyrfalcon eggs and hatchlings. Even brown bears may be dive-bombed. Humans, whether accidentally (automobile collisions or poisoning of carrion to kill mammalian scavengers) or intentionally (through hunting), are the leading cause of death for Gyrfalcons. Gyrfalcons that survive into adulthood can live up to 20 years of age.

As F. rusticolus has such a wide range, it is not considered a threatened species by the IUCN. It is not much affected by habitat destruction, but pollution, for instance by pesticides, depressed its numbers in the mid-20th century, and until 1994 it was considered "Near Threatened". Improving environmental standards in developed countries have allowed the birds to make a comeback, and today they are not considered rare or endangered.[5]

Interaction with humans

The Gyrfalcon has long associated with humans, who have found them useful primarily for hunting and latterly for such sports as falconry. It is today the official bird of Canada's Northwest Territories. The white falcon in the crest of the Icelandic Republic's coat of arms is a variety of Gyrfalcon.

In medieval times, the Gyrfalcon was considered a royal bird. It was highly prized as far away as the Sultan's court in Egypt. The geographer and historian Ibn Said al-Maghribi (d. 1286) described certain northern Atlantic islands west of Ireland where these falcons would be brought from, and how the Egyptian Sultan paid 1,000 dinars for each Gyrfalcon (or, if it arrived dead, 500 dinars).[6] Due to its rarity and the difficulties involved in obtaining it, in European falconry the Gyrfalcon was generally reserved for kings and nobles; very rarely was a man of lesser rank seen with a Gyrfalcon on his fist.[7]

In the 12th century AD the Jurchen tribes rebelled against the Chinese Liao Dynasty which was ruled by the Khitan. The primary cause was that the Khitan nobles, among whom swan hunting had become highly fashionable, extorted a big tax of Gyrfalcons (海东青 hǎidōngqīng in Chinese). Especially under the last Liao Emperor Yēlǜ Yánxĭ (耶律延禧), tax collectors were even entitled to use force to procure the demanded quantity of Gyrfalcons. The rebellion caught on, and the Jurchen under chieftain Wányán Āgǔdǎ (完颜阿骨打) annihilated the Liao empire in 1125, establishing the Jīn Dynasty in its stead.[8]

Gyrfalcons are today expensive to purchase, and thus owners and breeders may keep them secret to avoid theft. They can and often do fly long distances, and falconers may fit a radio-tracker in order to aid recovery. Wild Gyrfalcons are not much exposed to disease, and as a result have immune systems that are naive to many pathogens found around human environments. As a result, many Gyrfalcons taken from the wild quickly die of disease. Several generations of captive breeding from the survivors causes selection for a stronger immune system and thus better resistance to disease.[9]

Falcons are known to be very susceptible to avian influenza. Therefore an experiment was done with hybrid gyr-saker falcons, which found that 5 falcons vaccinated with a commercial H5N2 influenza vaccine survived infection with a highly pathogenic H5N1 strain, whereas 5 unvaccinated falcons died. Since both wild and captive gyrfalcons are valuable (for wildlife conservation and falconry, respectively), this means they can be protected from bird flu by vaccination. [10]

Notes

  1. ↑ Individual vagrancy can take birds for long distances. There is a story in the Unauthorized Biography of the Spring and Autumn of a hǎidōngqīng (海东青: Gyrfalcon) that succumbed to an arrow wound in the garden of Chen Hui Gong. Confucius recognized the arrow as one of the Sushen, whose fine stone arrowheads were a famous item of trade and tribute (RAM 2006). Although the Sushen's precise homeland at that time remains unknown, it was in the Manchuria region, no less than c.600 and perhaps more than 1000 km from the Lu capital of Qufu.
  2. ↑ In Scandinavian languages, it is generally named after its use in falconry, whereas the modern Dutch name giervalk is peculiarly ambiguous: Gier means "vulture", whereas gieren means changing the yaw angle to circle in the air.
  3. ↑ The allele combination producing the white morph seems to be recessive.
  4. ↑ Falco rusticolus candicans from northern Greenland and adjacent North America which is often very white; F. r. obsoletus from the southern Greenland into subarctic North America which is much darker, often brown or black; and F. r. islandus (Iceland), F. r. rusticolus (Scandinavia including the species' type locality, Sweden), as well as F. r. intermedius and F. r. grebnitzkii (Siberia), which all tend towards more or less dark "silver" coloration (Snow et al. 1998, Johnson et al. 2007).

References

  1. ↑ Helbig et al. (1994), Wink et al. (1998), Wink et al. (2004), Nittinger et al. (2005)
  2. ↑ White (1994), Snow et al. (1998)
  3. ↑ 3.0 3.1 Johnson et al. (2007)
  4. ↑ Miller (1927, 1935), Howard (1971), Emslie (1985)
  5. ↑ BLI (2008)
  6. ↑ Ibn Said al-Maghribi: Geographia (Arabic)
  7. ↑ Berners (1486)
  8. ↑ BMACH (2006)
  9. ↑ http://www.falconscanada.com/index.htm
  10. ↑ Lierz, Michael; Hafez M. Hafez, Robert Klopfleisch, Dörte Lüschow, Christine Prusas, Jens P. Teifke, Miriam Rudolf, Christian Grund, Donata Kalthoff, Thomas Mettenleiter, Martin Beer, and Timm Harder (November 2007). "Protection and Virus Shedding of Falcons Vaccinated against Highly Pathogenic Avian Influenza A Virus (H5N1)". Emerging Infectious Diseases (Centers for Disease Control) 13 (11): 1667. http://www.cdc.gov/EID/content/13/11/1667.htm. Retrieved 12 June 2010. 

Bibliography

External links