The snow bunting (Plectrophenax nivalis) is a passerine bird in the family Calcariidae. It is an Arctic specialist, with a circumpolar Arctic breeding range throughout the northern hemisphere. There are small isolated populations on a few high mountain tops south of the Arctic region, including the Cairngorms in central Scotland and the Saint Elias Mountains on the southern Alaska-Yukon border, as well as the Cape Breton Highlands. The snow bunting is the most northerly recorded passerine in the world.

Taxonomy

The snow bunting was formally described by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae. He placed it with the buntings in the genus Emberiza and coined the binomial name Emberiza nivalis. He specified the locality as Lapland. It is now placed in the genus Plectrophenax, described in 1882 by the Norwegian born zoologist Leonhard Stejneger with the snow bunting as the type species. The genus name Plectrophenax is from Ancient Greek , "cock's spur", and phenax "imposter", and the specific nivalis is Latin for "snow-white".

The snow bunting was formerly classified in the family Emberizidae, which included American sparrows, buntings, towhees and finches. All these species came into existence after a broad geologically recent radiation of passerine birds. However, it is now part of the narrower family Calcariidae, which also contains the longspurs. Despite the wide distribution of this species there are only very small differences between different phenotypes.

  • Plectrophenax nivalis nivalis (Linnaeus, 1758) – Arctic Europe, Arctic North America. Head white, rump mostly black with a small area of white.
  • Plectrophenax nivalis insulae Salomonsen, 1931 – Iceland, Faroe Islands, Scotland. Head white with a blackish collar, rump black.
  • Plectrophenax nivalis vlasowae Portenko, 1937 – Arctic Asia. Head white, rump mostly white.
  • Plectrophenax nivalis townsendi Ridgway, 1887 – Aleutian Islands, Kamchatka, coastal far eastern Siberia. As vlasowae, but slightly larger.

It is very closely related to the Beringian McKay's bunting (Plectrophenax hyperboreus), which differs in having even more white in the plumage. Hybrids between the two occur in Alaska, and they have been considered conspecific by some authors, though they are currently generally treated as separate species.

A hybrid with a Lapland longspur was photographed at St. Lewis Inlet, Newfoundland and Labrador, Canada, during spring migration in April 2011.

Description

thumb|right|A female snow bunting wintering atop Mount [[Agamenticus in York, Maine]]

The snow bunting is a sexually dimorphic, medium-sized passerine bird. It is ground-dwelling, and walks, runs and can hop if needed. It is fairly large and long-winged for a bunting. It measures 15 cm with a wingspan of and weights 30 to 40 grams.

This species is easily confused with McKay's bunting due to the similarity of their plumage and the occurrence of hybrids.

Vocalizations

thumb|Snow bunting's song

The call is a distinctive rippling whistle, per,r,r,rit, and the song is a brief but loud warble hudidi feet feet feew hudidi. The communication calls are done by both the male and the female and they tend to be emitted in flight or in the ground, while the males will often emit the song from a perching position or in a flight display. The males will start singing as soon as they will reach the breeding grounds, and will stop once they find a mate.

Within snow buntings, vocalizations in males are unique to each individual, although there is certain syllable sharing between one another. The uniqueness of each song reveals a capacity of recognition between individuals and has an effect in the individual fitness and reproductive success. This species is found in the high Arctic tundra of North America, Ellesmere Island, Iceland, higher mountains of Scotland, Norway, Russia, North Greenland, Siberia, Novaya Zemlya, and Franz Josef Land. During the winter, this bird migrates to the circumglobal northern temperate zone including the south of Canada, the northern United States, the coasts and plains of northern Europe in Great Britain, the Netherlands, Germany, Poland, Ukraine, and east to central Asia.

thumb|Snow bunting young using a building as protection

thumb|The same chicks eight days later

During the breeding period, the snow bunting looks for rocky habitats in the Arctic. During this period, buntings also look for a habitat rich in vegetation such as wet sedge meadows and areas rich in dryas and lichens.

Migration

The snow buntings migrate to the Arctic to breed and they are the first migrant species that arrives in these territories. The males will arrive first at the beginning of April, when the temperature can reach as low as . This early migration could be explained by the fact that this species is highly territorial and the quality of the nesting area is crucial to their reproductive success. Females will arrive four to six weeks later, when the snow starts to melt. They tend to migrate in small flocks and have an undulating flight at a moderate height.

Physiological adaptations

Right before the breeding season, snow buntings undergo significant physiological changes to prepare for their journey to higher Arctic regions. One of the most obvious changes is an increase in body weight. They undergo the process of hyperphagia, or increased food take, which builds up their fat reserves. Their overall fat mass increases by 30%, while their lean mass decreases by 15%. The size of their pectoralis muscle also increases so that they can increase shivering thermogenesis through muscle contractions. As they reach the Arctic, snow buntings must be ready to engage in breeding and courtship. Their fat reserves also provide energy for reproduction during this time. Once the breeding season is over, snow buntings lose most of their extra fat to fly back to the southern regions where they continue to live until next season.

Behaviour

Food and feeding

From the fall to the spring the snow bunting eats a variety of weeds such as knotweed, ragweed, amaranth, goosefoot, aster, and goldenrod and also eats various types of grass seeds. During this season it will forage in the snow collecting seeds from lower stems. During the summer their diet includes seeds of crowberry, bilberry, bistort, dock, poppy, purple saxifrage and invertebrates such as butterflies, true bugs, flies, wasps and spiders. The nestlings are fed exclusively on invertebrates. Snow buntings also prey on basking spiders by throwing rocks around and less regularly they will try to catch invertebrates in flight. The male will follow the female during her fertile period to make sure that she will not mate with any other male. The eggs are blue-green, spotted brown, and hatch in 12–13 days, and the young are already ready to fly after a further 12–14 days.