The northern hawk-owl or northern hawk owl (Surnia ulula) is a medium-sized true owl of the northern latitudes. It is non-migratory and usually stays within its breeding range, though it sometimes irrupts southward. It is one of the few owls that is neither nocturnal nor crepuscular, being active only during the day. This is the only living species in the genus Surnia of the family Strigidae, the "typical" owls (as opposed to barn owls, Tytonidae). The species is sometimes called simply the hawk owl; however, many species of owls in the genus Ninox are also called "hawk owls".
Taxonomy
The northern hawk-owl was formally described by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae under the binomial name Strix ulula. The owl is now the only species placed in the genus Surnia that was introduced in 1805 by André Duméril. The type species was designated by George Robert Gray in 1840 as the northern hawk-owl. The genus name is of unknown etymology and may simply have been invented by Duméril. The specific epithet ulula is Latin for a "screech owl".
A molecular phylogenetic study of the owls published in 2019 found that the northern hawk-owl is sister to a clade containing the pygmy owls in the genus Glaucidium.
Three subspecies are recognised: S. u. tianschanica Smallbones, 1906 – central Asia to northern China and northern Mongolia S. u. ulula (Linnaeus, 1758) – northern Eurasia S. u. caparoch (Müller, PLS, 1776) – northern North America
Description
Male northern hawk-owls are generally long and weigh about . Females are slightly bigger with a length of and a mass of about . Both male and female have similar wingspans of about . The northern hawk-owl plumage is relatively dark brown with an off-white spotting pattern on all dorsal parts of the body with the exception of the back of the neck which boasts a black v-shaped pattern. The underbelly is generally white or off-white which continues to the toes with brown bands on the breast and stomach. It also has a long tail with brown banding. The northern hawk-owl has a smokey white face with a black border, a flat head, yellow eyes and a yellow curved beak.
The northern hawk-owl has been said to resemble a hawk in appearance and in behavior. In North America, its appearance in flight is often considered similar to a Cooper's hawk (Accipiter cooperii). It has been suggested that this may be because the hawk-owl may partially fill an important diurnal niche similar to that of day hunters such as hawks.
Vocalization
Various calls are used by the different sexes in different situations. When attracting a mate the male usually lets out a rolled whistle of ulululululululul and a sound similar to tu-wita-wit, tiwita-tu-wita, wita, when perching at a potential nest site. The female's call is usually less constant and more shrill.
When alerting to danger, the northern hawk-owl lets out a sound similar to rike, rike, rike, rike. It also releases a high-pitched scream followed by a yip when an intruder is near to the nest. To warn of impending dangers to a fledgling, the hawk-owl will let out a noise similar to ki ki kikikikiki. Calls can vary in length from 15 s to 2 min.
Distribution and habitat
Three subspecies exist across the northern Holarctic. The North American subspecies S. u. caparoch spans from eastern Alaska through Canada to Newfoundland and in some areas extends south into northern United States. The other two subspecies are found in northeastern Europe and Siberia: S. u. tianschanica breeds in Central Asia reaching Xinjiang (China); and S. u. ulula resides across Siberia reaching its most eastern range.
Occasionally, S. u. caparoch can extend its territory as far south as northern Minnesota and many other states in the northern United States including more central states such as West Virginia, New York, and South Dakota. These southern forays into the northern United States are rare and generally occur during winter, or following an explosion in a population of prey. S. u. caparoch can occasionally be found in more southern areas such as Great Britain, southern Russia and Scandinavia, following explosions of prey.
Northern hawk-owls are unevenly distributed and highly variable throughout the boreal forest. They live mostly in open coniferous forests, or coniferous forests mixed with deciduous species such as larch, birch, poplar, and willow. They are found in muskegs, clearings, swamp valleys, meadows, or recently burnt areas, and generally avoid dense spruce-fir forests. Their winter habitat is usually the same as the breeding habitat.