The snowy owl (Bubo scandiacus), also known as the polar owl, the white owl and the Arctic owl, is a large, white owl of the true owl family. Snowy owls are native to the Arctic regions of both North America and the Palearctic, breeding mostly on the tundra. It has a number of unique adaptations to its habitat and lifestyle, which are quite distinct from other extant owls. One of the largest species of owl, it is the only owl with mainly white plumage. Males tend to be a purer white overall while females tend to have more extensive flecks of dark brown. Juvenile male snowy owls have dark markings and may appear similar to females until maturity, at which point they typically turn whiter. The composition of brown markings about the wing, although not foolproof, is the most reliable technique for aging and sexing individual snowy owls.
Most owls sleep during the day and hunt at night, but the snowy owl is often active during the day, especially in the summertime. The snowy owl is both a specialized and generalist hunter. Its breeding efforts and global population are closely tied to the availability of tundra-dwelling lemmings, but in the non-breeding season, and occasionally during breeding, the snowy owl can adapt to almost any available prey – most often other small mammals and northerly water birds, as well as, opportunistically, carrion. Snowy owls typically nest on a small rise on the ground of the tundra.Hume, R. (1991). Owls of the world. Running Press, Philadelphia. The snowy owl lays a very large clutch of eggs, often from about 5 to 11, with the laying and hatching of eggs considerably staggered. Despite the short Arctic summer, the development of the young takes a relatively long time and independence is sought in autumn.
The snowy owl is a nomadic bird, rarely breeding at the same locations or with the same mates on an annual basis and often not breeding at all if prey is unavailable. A largely migratory bird, snowy owls can wander almost anywhere close to the Arctic, sometimes unpredictably irrupting to the south in large numbers. Given the difficulty of surveying such an unpredictable bird, there was little in-depth knowledge historically about the snowy owl's status;Bent, A. C. (1938). Life Histories of North American Birds of Prey (part 2), Orders Falconiformes and Stringiformes (Vol. 170). US Government Printing Office. however, 2020s data suggests the species is declining precipitously. Whereas the global population was once estimated at over 200,000 individuals, 2010s–2020s data suggests that there are probably fewer than 100,000 individuals globally and that the number of successful breeding pairs is 28,000 or even considerably less. While the causes are not well understood, numerous, complex environmental factors often correlated with global warming are probably at the forefront of the fragility of the snowy owl's existence.
Taxonomy The snowy owl was one of the many bird species originally described by Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae, where it was given the binomial name Strix scandiaca. The genus name Bubo is Latin for "horned owl" and scandiacus is Neo-Latin for "of Scandinavia". The former generic name Nyctea is derived from Greek meaning "night". Linnaeus originally described the different plumages of this owl as separate species, with the male specimens of snowy owls being considered Strix scandiaca and the likely females considered as Strix nyctea. Into the 21st century, the snowy owl was regarded as the sole member of a distinct genus, as Nyctea scandiaca, but mtDNA cytochrome b sequence data shows that it is very closely related to the horned owls in the genus Bubo and the species is thusly often considered inclusive with that genus;Wink, M. & Heidrich, P. (2000). "Molecular systematics of owls (Strigiformes) based on DNA-sequences of the mitochondrial cytochrome b gene", pp. 819–828 in: Chancellor, R.D. & Meyburg, B.U. eds. (2000). Raptors at Risk. Proceedings of the V World Conference on Birds of Prey and Owls. Midrand, Johannesburg, 4–11 August 1998. WWGBP & Hancock House, Berlin & Blaine, Washington.Penhallurick, J. M. (2002). "The taxonomy and conservation status of the owls of the world: a review". Ecology and conservation of owls. CSIRO, Collingwood, pp. 343–354. however, some authorities debate this classification, still preferring Nyctea. Often authorities are motivated to retain the separate genus on the grounds of osteological distinctions.Ford, N. L. (1967). A systematic study of the owls based on comparative osteology. PhD diss, Univ. of Michigan, Ann Arbor.
Genetic testing revealed a reasonably distinct genetic makeup for snowy owls, being about 8% genetically distinct from other Bubo owls, perhaps giving credence to those who count the species as separate under Nyctea; however, a fairly recent shared origin in evolutionary history has been illustrated through a combination of genetic study and fossil review and there is little, other than osteology of the tarsometatarsus, to outright distinguish the snowy owl from other modern species like the Eurasian eagle-owl (Bubo bubo). Genetic testing has indicated that the snowy owl may have diverged from related species at around 4 million years ago. Furthermore, it has determined that the living species genetically most closely related to the snowy owl is the great horned owl (Bubo virginianus).
On a broader scale, owls in general have, through genetic materials, been determined to be a highly distinct group, with outwardly similar groups such as Caprimulgiformes revealed to not be at all closely related. Within the owl order, typical owls are highly divergent from barn-owls. Furthermore, the Bubo genus likely clustered at some point during the evolutionary process with other largish owls, such as Strix, Pulsatrix and Ciccaba, based on broad similarities in their voice, reproductive behaviors (i.e. hooting postures) and a similar number and structure of chromosomes and autosomes. A number, but not all, of extant typical owls seem to have evolved from an ancient shared common ancestor with the Bubo owls. In addition to the question of relationship of the traditional Bubo owls to the snowy owls, ongoing ambiguity of the relationship of other similarly large-sized owls has been persistent. These have sometimes either been included in the genus or within separate genera, i.e. the Ketupu or fish owls and the Scotopelia or fishing owls. Despite the adaptive distinctions, the grouping of these large owls (i.e. Bubo, snowy, fish and perhaps fishing owls) appears to be borne out via research of karyotypes.Owls of the World: A Photographic Guide by Mikkola, H. Firefly Books (2012),
The fossil history of snowy owls is fairly well documented despite some early confusion on how to distinguish the skeletal structure of the snowy owls from eagle-owls. It was determined that the snowy owl once was distributed much more widely and far farther to the south during the Quaternary glaciation when much of the Northern Hemisphere was in the midst of an ice age. Fossil records shows that snowy owls once could be found in Austria, Azerbaijan, Czechoslovakia, England, France, Germany, Hungary, Italy, Poland, Sardinia and Spain as well as in the Americas in Cape Prince of Wales, Little Kiska Island, St. Lawrence Island, and in Illinois. In the Late Pleistocene the range expanded southward even more so to Bulgaria (80,000–16,000 years, Kozarnika Cave, W Bulgaria). and much of the Italian Peninsula. Pleistocene era fossils from France, i.e. B. s. gallica, showed that the snowy owls of the time were somewhat bulkier (although still notably smaller than contemporary eagle-owls of the times, which were larger than the modern-day eagle-owls) and osteologically more sexually dimorphic in size than the modern form (9.9% dimorphism in favor of females in the fossils against 4.8% in the same features).Andrews, P. (1990). Owls, caves and fossils. Chicago: University of Chicago Press. There are no subspecific or other geographical variations reported in the modern snowy owls, with individuals of vastly different origins breeding together readily due to their nomadic habits. Despite apparent variations in body size, environmental conditions are the likely variant rather than genetics. No evidence could be found of phylogeographic variation in snowy owls upon testing. Furthermore, the snowy owl appears to have a similar level of genetic diversity as other European owls.Marthinsen, G., Wennerberg, L., Solheim, R., & Lifjeld, J. T. (2009). Snowy owls (Bubo scandiacus) constitute one panmictic population. University of Oslo.
Hybrids Snowy owls are not known to interbreed with other owl species in the wild, and accordingly, no hybrids of snowy owls and other owl species have yet been sighted in the wild. However, a hobby falconer in Kollnburg, Germany, bred hybrids from a male snowy owl and a female Eurasian eagle-owl (Bubo bubo) in 2013."Schnuhu": Überraschende Kreuzung – Ich bin Bayerns süßester Fratz!. tz.de Retrieved on 7 October 2016 The two resulting male hybrid owls possessed the prominent ear-tufts (generally visually absent in snowy owls), general size, orange eyes, and the same pattern of black markings on their plumage from their Eurasian eagle-owl mother, while retaining the generally black-and-white plumage colours from their snowy owl father. The hybrids were dubbed "Schnuhus" from the German words for snowy owl and Eurasian eagle-owl (Schnee-Eule and Uhu, respectively). As of 2014, the hybrids had grown to maturity and were healthy.
Description
The snowy owl is mostly white. They are purer white than predatory mammals such as polar bears (Ursus maritimus) and Arctic fox (Vulpes lagopus). Often when seen in the field, these owls can resemble a pale rock or a lump of snow on the ground. They usually appear to lack ear tufts but very short (and probably vestigial) tufts can be erected in some situations, perhaps most frequently by the female when she is sitting on the nest. The ear tufts measure about and consist of about 10 small feathers. The snowy owl has bright yellow eyes. The head is relatively small and, even for the relatively simply adapted hearing mechanism of a Bubo owl, the facial disc is shallow and the ear is uncomplicated. 1 male had ear slits of merely on left and on the right.
Females are almost invariably more duskily patterned than like-age males. In mature males, the upper parts are plain white with usually a few dark spots on the miniature ear-tufts, about the head and the tips of some primaries and secondaries whilst the underside is often pure white. Despite their reputation for being purely white, only 3 out of 129 Russian museum specimens of adult males showed an almost complete absence of darker spots. The adult female is usually considerably more spotted and often slightly barred with dark brown on the crown and the underparts. Her flight and tail feathers are faintly barred brown whilst the underparts are white in base color with brown spotting and barring on the flanks and upper breast. In confusingly plumaged snowy owls, the sex can be determined by the shape of wing markings, which manifest as bars more so in females and spots in males. However, the very darkest males and the lightest females are nearly indistinguishable by plumage.