Northern saw-whet owl | |
---|---|
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Aves |
Order: | Strigiformes |
Family: | Strigidae |
Genus: | Aegolius |
Species: | A. acadicus |
Binomial name | |
Aegolius acadicus (Gmelin, JF, 1788) | |
Subspecies | |
Aegolius acadicus acadicus Contents | |
Geographical distribution of the Northern saw-whet owl. Year-round Nonbreeding Nonbreeding (scarce) | |
Synonyms | |
Nyctala acadica |
The northern saw-whet owl (Aegolius acadicus) is a species of small owl in the family Strigidae. The species is native to North America. Saw-whet owls of the genus Aegolius are some of the smallest owl species in North America. They can be found in dense thickets, often at eye level, although they can also be found some 20 ft (6.1 m) up. Saw-whets are often in danger of being preyed upon by larger birds of prey. The northern saw-whet owl is a migratory bird without any strict pattern.
The northern saw-whet owl was formally described in 1788 by the German naturalist Johann Friedrich Gmelin in his revised and expanded edition of Carl Linnaeus's Systema Naturae . He placed it with the other owls in the genus Strix and coined the binomial name Strix acadicus. [3] Gmelin based his description on the "Acadian owl" from Nova Scotia that had been described and illustrated in 1781 by the English ornithologist John Latham in his multi-volume work A General Synopsis of Birds. [4] [5] The northern saw-whet owl is now one of five species placed in the genus Aegolius that was introduced in 1829 by the German naturalist Johann Jakob Kaup. [6] [7] The genus name is Latin for a screech owl, the word came from the Ancient Greek aigōlios meaning "a bird of ill omen". The specific epithet acadicus is from "Acadia", the name of a former French colony in Nova Scotia. [8]
Two subspecies are recognised: [7]
The scientific description of one of the subspecies of this owl is attributed to the Rev. John Henry Keen, a missionary in Canada in 1896. [9] Adults are 17–22 cm (6.7–8.7 in) long with a 42–56.3 cm (16.5–22.2 in) wingspan. [10] [11] They can weigh from 54 to 151 g (1.9 to 5.3 oz) with an average of around 80 g (2.8 oz), [12] [13] making them one of the smallest owls in North America. [14] They are similar in size to the American robin. Northern saw-whet owls do not exhibit sexual dimorphism through their plumage and were often sexed by size dimorphism, where females are larger than males. Females on average weigh 100 g and males on average weigh 75 g. [15] Northern saw-whet owls have porphyrin pigments in their flight feathers. When exposed to a UV light, feathers on the ventral side of the wing fluoresce a neon pink. This is used in order to estimate molt and age in adults. [16]
The northern saw-whet owl has a round, light, white face with brown and cream streaks; they also have a dark beak and yellow eyes. Juveniles have a dark brown head and wings, and a tawny rust-colored breast and belly. There is also a distinct white, Y-shaped coloration between their eyes. [17] The juveniles can often be confused with the juvenile Boreal owls. Northern saw-whet owls resemble the short-eared owl, because they also lack ear tufts, but are much smaller. The underparts are pale with dark shaded areas; the upper parts are brown or reddish with white spots. They are quite common, but hard to spot.
There are two subspecies of the northern saw-whet owl: the Aegolius acadicusacadicus found all around North America and the non-migratory Aegolius acadicus brooksi endemic to the Haida Gwaii archipelago in British Columbia. [18] A. a. brooksi is identified by a darker, buffier plumage [17] and has been proposed as a separate species, the Haida Gwaii saw-whet owl. Isolated populations of northern saw-whet owls in the Allegheny Plateau and Southern Appalachian Mountains have been found to be morphologically different to mid-range owls and as genetically distinct as the subspecies A.a.brooksi in British Columbia. [19]
The northern saw-whet owl makes a repeated tooting whistle sound. Some say they sound like a saw being sharpened on a whetstone. [20] They usually make these sounds to find a mate, so they can be heard more often April through June when they are looking for mates. Despite being more common in spring, they do vocalize year round. The advertising too-too-too call has been heard up to 300 meters away through forest. [19] At least 11 different vocalizations have been reported for the northern saw-whet owl. These include the Advertising call, [21] the Rapid call, [22] Whine, [23] Ksew call, Tssst call, Squeaks, [24] Twittering call (similar to an American Woodcock), Guttural chuck, and begging calls of nestlings. Two additional calls only recorded in brooksi include the Transition Call and Alternate Whine. Non-vocal sounds such as bill snapping are used as a warning call by adults, juveniles and nestlings usually when approached up close or when in the hand. [19]
The bird's habitat is coniferous forests, sometimes mixed or deciduous woods, across North America. Most birds nest in coniferous type forests of the North but winter in mixed or deciduous woods. They also love riparian areas because of the abundance of prey there. [25] They live in tree cavities and old nests made by other small raptors. Some are permanent residents, while others may migrate south in winter or move down from higher elevations. Their range covers most of North America south of the boreal forest, including southeastern and southcentral Alaska, southern Canada, most of the United States and the central mountains in Mexico. [26]
Some have begun to move more southeast in Indiana and neighboring states. Buidin et al. did a study of how far north the northern saw-whet owls breed and they found that they can breed northward of 50° N, farther than ever recorded before. [27] Their range is quite extensive and they can even breed in the far north where most birds migrate from to breed. They are an adaptive species that can do well in the cold.
There are two semi-isolated permanent populations in the eastern part of the United States. This first is a population along the West Virginia border in the Allegheny Plateau. The second population is in the higher elevations (>4000 ft) of the southern Appalachian Mountains of western North Carolina, eastern Tennessee, and southwestern Virginia. Although there are abundant populations in the Northern and Western Regions of North America, in some counties of North Carolina, it is currently listed as a threatened species due to a decline in suitable habitat. [28] This is due to loss of boreal forests from hemlock woolly adelgid, logging, and pollution. [28]
Northern saw-whet owls lay about four or six white-colored eggs in natural tree cavities or woodpecker holes. Males will often sing from a nest site [19] and cache food in nest sites in order to attract a female. [15] The father does the hunting while the mother watches and sits on her eggs. Females can have more than one clutch of eggs each breeding season with different males. Once the offspring in the first nest have developed their feathers the mother will leave the father to care for them and go find another male to reproduce with. [25] This type of mating is sequential polyandry. They compete with boreal owls, starlings and squirrels for nest cavities and their nests may be destroyed or the nestlings eaten by those creatures as well as nest predators such as martens and corvids. Saw-whet owls of all ages may be predated by any larger species of hawks or owls, of which there are at least a dozen that overlap in range including Accipiter hawks, which share with the saw-whet owls a preference for wooded habitats with dense thickets or brush. [11]
In 2014 nesting northern saw-whet owls were found in breeding nest boxes in the Southern Appalachian mountains. This is the most southeastern known breeding area in the United States. [15]
The northern saw-whet owl has vertically asymmetrical ears and different shapes of the ear openings. Because the sound reaches the ears at a different time and is of different intensity, the northern saw-whet owl can very precisely localize its prey. Such accurate sound localization allows it to hunt in complete darkness by hearing alone. [29] [30] A study by Beatini et al showed that the northern saw-whet owl had a possible frequency sensitivity of 0.7 to 8.6 kHz with the best sensitivity ranging from 1.6 to 7.1 kHz. [31] This allows it to hunt in the dark purely by sound. The birds wait on a high perch at night and swoop down on prey. They mainly eat small organisms with a strong focus on small mammals in their diet. Swengel and Swengel (1992) reviewed ten studies that found northern saw-whet owls eating almost exclusively mammals (88% to 100%), with most of the mammals being rodents (85% to 99+%). Specifically in their Wisconsin study, the Swengels counted saw-whet owls as most often eating deer mice (Peromyscus; ~68% of captured prey), voles (Microtis pennsylvunicus and M. ochrogaster; ~16%), and shrews (~9%; Blarina brevicauda and Sorex cinereus). [32] A similar study by Holt and Leroux (1996) in Montana found saw-whet owls eating more voles (60%) than other mammal species. [33] Engel et al. (2015) also found in the saw-whet owl a strong preference for small mammals (89%), with 55% of prey being two species of voles.
Holt and Leroux compared the eating habits of northern saw-whet owls to northern pygmy owls and found that they prey on different animals for their main food source, with the saw-whet owl's diet 98% small mammals, while for pygmy owls over one-third of their prey was birds. Their study concluded that these owls could adapt depending on the prey and also with the other predators in the areas where they live. Engel et al. (2015) in Chain O'Lakes State Park, Illinois, during the winter of 1987–88, compared northern saw-whet owls to long-eared owls. Engel confirmed the saw-whet owl's strong preference for small mammals. Their diet appeared varied in the winter, and was less tied to one mammal than was the long-eared owl; at times, northern saw-whet owls hunted larger prey, such as the meadow vole (M. pennsylvanicus). [34]
Other mammals preyed on occasionally include shrews, squirrels (largely chipmunks and red squirrels), various other mice species, flying squirrels, moles and bats. Also supplementing the diet are small birds, with passerines such as swallows, sparrows, kinglets and chickadees favored. However, larger birds, up to the size of rock dove (which are typically about 4 times as heavy as a saw-whet owl) can even be taken. [11] On the Pacific coast they may also eat crustaceans, frogs and aquatic insects. Like many owls, these birds have excellent hearing and exceptional vision in low light.
This section may contain information not important or relevant to the article's subject.(December 2020) |
An adult female northern saw-whet owl was found dehydrated and hungry within the wrapped branches of the Rockefeller Center Christmas Tree during its installation on November 16, 2020. The bird was discovered by workers who transported the spruce 170 miles (274 km) from Oneonta, New York to New York City. The feathered stowaway, named Rockefeller (Rocky), endured the three-day road trip and generated much public interest and media coverage. She was taken to a wildlife center for a check-up and nursed to full strength before being released on the grounds of the wildlife center in Saugerties, New York. [35] Rocky gained more fame when Frontier Airlines announced that her image will be featured on the aircraft tails in their fleet. [36]
The snowy owl, 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 that 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 to age and sex individual snowy owls.
The rough-legged buzzard (Europe) or rough-legged hawk is a medium-large bird of prey. It is found in Arctic and Subarctic regions of North America, Europe, and Russia during the breeding season and migrates south for the winter. It was traditionally also known as the rough-legged falcon in such works as John James Audubon's The Birds of America.
The long-eared owl, also known as the northern long-eared owl or, more informally, as the lesser horned owl or cat owl, is a medium-sized species of owl with an extensive breeding range. The genus name, Asio, is Latin for "horned owl", and the specific epithet, otus, is derived from Greek and refers to a small eared owl. The species breeds in many areas through Europe and the Palearctic, as well as in North America. This species is a part of the larger grouping of owls known as typical owls, of the family Strigidae, which contains most extant species of owl.
The northern hawk-owl or northern hawk owl 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. The species is sometimes called simply the hawk owl; however, many species of owls in the genus Ninox are also called "hawk owls".
The great horned owl, also known as the tiger owl or the hoot owl, is a large owl native to the Americas. It is an extremely adaptable bird with a vast range and is the most widely distributed true owl in the Americas. Its primary diet is rabbits and hares, rats and mice, and voles, although it freely hunts any animal it can overtake, including rodents and other small mammals, larger mid-sized mammals, birds, reptiles, amphibians, and invertebrates.
The barred owl, also known as the northern barred owl, striped owl or, more informally, hoot owl or eight-hooter owl, is a North American large species of owl. A member of the true owl family, Strigidae, they belong to the genus Strix, which is also the origin of the family's name under Linnaean taxonomy. Barred owls are largely native to eastern North America, but have expanded their range to the west coast of North America where they are considered invasive. Mature forests are their preferred habitat, but they can also acclimatise to various gradients of open woodlands. Their diet consists mainly of small mammals, but this species is an opportunistic predator and is known to prey upon other small vertebrates such as birds, reptiles, and amphibians, as well as a variety of invertebrates.
The eastern screech owl or eastern screech-owl, is a small owl that is relatively common in Eastern North America, from Mexico to Canada. This species resides in most types of woodland habitats across its range, and is relatively adaptable to urban and developed areas compared to other owls. Although it often lives in close proximity to humans, the eastern screech owl frequently avoids detection due to its strictly nocturnal habits.
Cooper's hawk is a medium-sized hawk native to the North American continent and found from southern Canada to Mexico. This species is a member of the genus Accipiter, sometimes referred to as true hawks, which are famously agile, relatively small hawks common to wooded habitats around the world and also the most diverse of all diurnal raptor genera. As in many birds of prey, the male is smaller than the female. The birds found east of the Mississippi River tend to be larger on average than the birds found to the west. It is easily confused with the smaller but similar sharp-shinned hawk.
The ancient murrelet is a bird in the auk family. The English term "murrelet" is a diminutive of "murre", a word of uncertain origins, but which may imitate the call of the common guillemot. Ancient murrelets are called "ancient" because they have grey on the back like a shawl, as worn by the elderly.
The boreal owl or Tengmalm's owl is a small owl in the "true owl" family Strigidae. It is known as the boreal owl in North America and as Tengmalm's owl in Europe after Swedish naturalist Peter Gustaf Tengmalm or, more rarely, Richardson's owl after Sir John Richardson.
Voles are small rodents that are relatives of lemmings and hamsters, but with a stouter body; a longer, hairy tail; a slightly rounder head; smaller eyes and ears; and differently formed molars. They are sometimes known as meadow mice or field mice in North America.
Aegolius is a genus of small true owls. The genus name is from Latin, aegolius, is a type of screech owl that was thought to be a bird of ill omen.
The buff-fronted owl is a small owl. It is found in widely separated areas in every South American country except French Guiana and Suriname.
The unspotted saw-whet owl is a small "typical owl" in subfamily Surniinae. It is found in Costa Rica, El Salvador, Guatemala, Mexico, and Panama.
The spotted eagle-owl, also known as the African spotted eagle-owl and the African eagle-owl, is a medium-sized species of owl, one of the smallest of the eagle owls. Its length is 45 cm (18 in) and its weight is from 454 to 907 grams. It has a 100 to 140 cm wingspan. The facial disk is off-white to pale ochre and the eyes are yellow. It has prominent ear-tufts, and the upper body is dusky brown, the lower parts off-white with brown bars. Prior to 1999 the spotted eagle-owl was considered conspecific with the greyish eagle-owl, but now it is classed as a separate species.
The barking owl, also known as the winking owl, is a nocturnal bird species native to mainland Australia and parts of New Guinea and the Moluccas. They are a medium-sized brown owl and have a characteristic voice with calls ranging from a barking dog noise to an intense human-like howl.
The powerful owl, a species of owl native to south-eastern and eastern Australia, is the largest owl on the continent. It is found in coastal areas and in the Great Dividing Range, rarely more than 200 km (120 mi) inland. The IUCN Red List of Threatened Species also refers to this species as the powerful boobook.
The northern pygmy owl is a small owl native to western North America.
The lesser sooty owl is a medium-sized barn owl endemic to the wet tropics region of Australia. Once considered a subspecies of the greater sooty owl, it is distinguished by its dark plumage, heavier spotting, and higher-pitched call. The lesser sooty owl has a limited range within northeastern Australia and primarily lives in dark, sheltered areas of the rainforest.
Justin Lee Rasmussen, Spencer G. Sealy, and Richard J. Cannings