Northern saw-whet owls impact the populations of small mammals that they eat. They also host at least nine species of external parasites.
Great horned owls are the only species that has been directly observed predating northern saw-whet owls. However, other large owls, such as long-eared owls and barred owls presumably also prey on northern saw-whet owls.
When approached by a predator or a human at night, northern saw-whet owls give a “ksew” call. During the day, they assume an erect posture and flatten their feathers against the body. If the predator continues to approach, they usually exhibit a “fright” reaction, bobbing the head, shifting from foot to foot, defecating, bill-snapping and finally flying away.
Known Predators:
Northern saw-whet owls are the smallest owls in eastern North America. At approximately 75 g, males weigh about as much as an American robin. Females weigh slightly more, at about 100g. The body lengths of males and females are 18 to 20 cm and 20 to 21.5 cm respectively. The wingspan of an adult ranges from 45 to 60 cm Northern saw-whets have dark-colored bills, eyes with yellow-pigmented irises, heavily feathered legs and feet, a tail with three bars, and a wide, reddish-brown body with white streaks on the abdomen. Their large, round heads are reddish brown to brown, have a large, grayish facial disk in the center and are streaked with white on the top. The neck is speckled with white. Northern saw-whet owls depend on this plumage for camouflage while roosting and hunting. .
Male and female saw-whet owls are similar in appearance, though females are slightly larger than males. Juveniles are chocolate-brown with a pattern of large white spots above their bills that extend over their eyes.
There are two recognized subspecies of northern saw-whet owl (Aegolius acadicus). Aegolius acadicus brooksi is found only on Queen Charlotte Island in British Columbia. It is similar to Aegolius acadicus acadicus, which is found throughout the rest of the range, except that the underparts are buff instead of white. Other than this subspecies, there is little geographic variation in appearance.
Range mass: 65 to 110 g.
Range length: 18 to 21.5 cm.
Range wingspan: 45 to 60 cm.
Other Physical Features: endothermic ; bilateral symmetry ; polymorphic
Sexual Dimorphism: female larger
Average basal metabolic rate: 0.654 W.
Captive saw-whet owls have lived as long as 16 years. In the wild, the longest known lifespan of a northern saw-whet owl was 7 ears.
Range lifespan
Status: wild: 7 (high) years.
Range lifespan
Status: captivity: 16 (high) years.
Average lifespan
Status: wild: 124 months.
Northern saw-whet owls inhabit woodlands of all types throughout their range. Though they seem to be most abundant in coniferous forests, they are also common in deciduous and mixed conifer-deciduous forests. During migration and winter, saw-whet owls inhabit a wide variety of habitats over a range of altitudes and latitudes. They may be found in rural or even suburban environments. The primary habitat requirements seem to be perches for hunting and dense vegetation for roosting.
Habitat Regions: temperate
Terrestrial Biomes: taiga ; forest
Other Habitat Features: suburban ; agricultural ; riparian
Northern saw-whet owls are found only in North America. Their breeding range includes southern Alaska, southern Canada, most of the United States and some high elevation sites in central Mexico.
Biogeographic Regions: nearctic (Native ); neotropical (Native )
Northern saw-whet owls hunt at night, from about 30 minutes after sunset to about 30 minutes before sunrise. They hunt from a low perch, detecting prey by sight and sound. Northern saw-whet owls have excellent hearing; their asymmetrical skull allows them to locate prey using sound alone. When a prey item is located, the owl drops out of the perch onto the prey, capturing it with the talons. The prey is torn apart and eaten in pieces. Larger prey may be partially eaten and stored on a branch to eat over the course of several hours.
The northern saw-whet owl diet consists primarily of small mammals, particularly deer mice. Voles, red-backed voles, shrews (g. Sorex, Blarina and Cryptotis), shrew-moles, pocket-mice, harvest-mice, bog lemmings, heather voles, red tree voles, jumping mice and house mice are also common prey items. Juveniles of larger mammals, including pocket-gophers, chipmunks and squirrels (Tamiasciurus and Glaucomys) are occasionally taken, as are insects, such as beetles and grasshoppers. Small birds are also occasionally taken, primarily during migration when they are active at night.
Animal Foods: birds; mammals; insects
Foraging Behavior: stores or caches food
Primary Diet: carnivore (Eats terrestrial vertebrates)
Northern saw-whet owls help humans by killing rodents that many people consider to be pests.
Positive Impacts: controls pest population
There are no known adverse affects of northern saw-whet owls on humans.
Global population estimates for northern saw-whet owls range from 200,000 to 600,000 individuals. Though population trends have not been studied, populations of northern saw-whets are probably declining slowly due to habitat loss. Starvation and parasites are documented causes of nestling mortality. Adults are frequently killed by collision with vehicles.
Northern saw-whet owls are protected under the U.S. Migratory Bird Act and CITES Appendix II. They are ranked as a species of least concern by the IUCN, and are not protected under the U.S. Endangered Species Act.
US Migratory Bird Act: protected
US Federal List: no special status
CITES: appendix ii
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
Northern saw-whet owls communicate and perceive their environment using touch, sound and vision. They detect prey by sight and sound. In fact, their hearing is so well developed that they can locate prey by hearing alone. Northern saw-whets use visual cues and vocalizations to communicate. For example, males with neighboring territories may exchange calls to establish territorial boundaries. During courtship, males vocalize to attract a mate, and pairs sometimes allopreen (preen each others feathers), using touch to strengthen or establish a pair bond.
Communication Channels: visual ; tactile ; acoustic
Perception Channels: visual ; tactile ; acoustic ; chemical
The Northern Saw-Whet Owl's common name comes from the "skiew" call it makes when it is alarmed. This call is said to sound like a saw being whetted.
Northern saw-whet owls are typically monogamous, though polygyny can occur when prey are abundant. It is likely that females of this species are sequentially polyandrous, leaving the male and nestlings during to mate with another male and raise a second brood. Though this behavior most likely occurs, it has not been confirmed. There is no evidence that pairs remain together for more than one season.
Males establish a territory and begin advertising for a female in late winter and early spring. Males advertise by calling to a female who may call back if interested in the male. Pairs have been seen allopreening (tending to the feathers of one another), which may serve to build a pair bond.
Mating System: monogamous
Northern saw-whet owls breed between March and July. Males begin advertising for a mate by calling in late winter and early spring. Once a pair has formed, the female selects a nest site. The nests are 2 to 12 m high, usually in natural cavities or abandoned woodpecker holes, often ones made by Northern Flickers and Hairy Woodpeckers. The female lays 4 to 7 (usually 5 or 6) eggs at two-day intervals. She also incubates the eggs, beginning soon after the first egg is laid. Meanwhile, the male brings her food and defends the territory. The eggs hatch after 26 to 28 days of incubation. The chicks are altricial at hatching; their eyes remain closed for the first 7 to 10 days and they must be brooded by the female. The male provides food to the female, who tears it into pieces and feeds it to the chicks until they are about 18 days old. After this, the female leaves the nest to roost elsewhere, and the male, and sometimes the female, continues to provide food to the chicks. The chicks leave the nest when they 4 to 5 weeks old. They are able to fly reasonably well at this time, but continue to be fed by the male for at least a month afterward. The young become independent from the parents 6 to 8 weeks after fledging. Juveniles complete their first molt and grow adult plumage when they are one year old. They also become sexually mature and may begin breeding at one year old.
Breeding interval: Northern saw-whet owls breed once yearly.
Breeding season: Northern saw-whet owls breed between March and July.
Range eggs per season: 4 to 7.
Range time to hatching: 26 to 28 days.
Range fledging age: 4 to 5 weeks.
Range time to independence: 6 to 8 weeks.
Average age at sexual or reproductive maturity (female): 1 years.
Range age at sexual or reproductive maturity (male): 1 (low) years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous
Average eggs per season: 5.
There is a clear division of parental responsibilities by northern saw-whet owls. The female selects the nest site, lays and incubates the eggs for 26 to 28 days and broods the chicks for at least 18 days. She also tears food up into smaller pieces and feeds it to the chicks. During this time, the male provides all of the food to the female and the chicks, and protects the nest area.
After 18 days, the female may join the male in providing food to the chicks, or she may leave the nest area completely, presumably to find another mate and raise a second brood. The male continues to feed the chicks for at least a month.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Protecting: Female); pre-weaning/fledging (Provisioning: Male, Protecting: Male, Female); pre-independence (Provisioning: Male, Female, Protecting: Male, Female)
At just 8 inches in length, the Northern Saw-whet Owl is one of the smallest owl species in North America. Like most owls, this species possesses short legs, rounded wings, large yellow eyes, and a disk-shaped face. Apart from its small size, it may best be identified by its coloration, which is brown spotted with white above and white streaked with brown below and on the face. The Northern Saw-whet Owl breeds primarily in Southern Canada and the northern tier of the United States. Breeding populations also exist at higher elevations in the western U.S. and in the Blue Ridge and Great Smoky Mountains in the southeast. During winter, this species expands its range southward and into lower elevations, including the coastal southeast, the Great Plains, and the southwest. The Northern Saw-whet Owl inhabits forests across the northern part of the continent, and each geographic region in which this species may be found has forests with a different mix of trees. Regardless of the exact species present, this owl prefers forests that are composed either entirely of evergreen trees or of a mix of evergreen and deciduous tree species. In winter, individuals which move outside the species’ breeding range are less tied to a particular habitat type, relocating as new sources of prey become available. Like most owls, the Northern Saw-whet Owl hunts small mammals, including mice, shrews, and voles. This owl uses its excellent hearing to locate prey on the ground in order to fly down and capture it with its talons. Also, like most owls, this species hunts almost exclusively at night, making it difficult to observe. Northern Saw-whet Owls are most visible roosting high in trees during the day or while producing toot-like calls at dusk.
Northern Saw-whet Owls (Aegolius acadicus) reside in forests across the United States, southern Canada and central Mexico. They can be found in different habitats based on the time of year. Saw-whet’s prefer mature forests with underbrush for foraging, riverside habitat in close proximity, deciduous trees to nest in, and roosting in opaque conifers (Cornell Lab of Ornithology). Breeding habitat is usually someplace wet or swampy such as cedar groves, swamps, alder thickets and Tamarac bogs (Lewis, 2015). They nest in a broad range of woodland habitats including deciduous forests, riverside forests, coniferous swamps, savannahs, and shrubby habitats. As secondary-cavity nesters, Northern Saw whet Owls commonly use abandoned Northern Flicker and Pileated Woodpecker holes, but will also use artificial nest boxes; they will not use the same site two years in a row (Kaufman, 2014). The nesting holes that the Northern Saw-whet Owl prefer during the need to have a diameter of 7 cm or larger (Nature Serve Explorer). The nesting site is usually 15-60 ft above ground, Outside of the breeding season, owls may be found in brushy areas, open buildings, dense growth, and arid scrub. During winter they often roost in dense evergreens usually near the trunk.
Eastern populations are most often found at lower elevations in the winter while those in the west reside in mature forests from 1,000 to over 10,000 feet in altitude. However, lower elevation habitats have been used in the winter months for western birds as well (Owling.com, 2001). The terrestrial biomes that this owl is found in encompass forest and taiga biomes, and the habitat is generally temperate forests. Northern saw-whet owls can be found in suburban as well as rural environments. This owl can live in almost any habitat as long as there is dense vegetation and perches for roosting and hunting. They can also be found in agricultural, suburban, or riparian habitats (Yan, 2001).
Changes in habitat and the time of year may influence the diet of the Northern Saw-whet Owl (Aegolius acadicus). These owls inhabit deciduous, coniferous, and mixed forests throughout the year and eat an array of different animals and insects. Saw-whet Owls most commonly eat small rodents including deer mice and voles - but they have also been known to eat birds and other small mammals (Swengel and Swengel, 1992). Mammal prey also includes woodland speciessuch of mice, jumping mice, chipmunks, and shrews.. Other mammal prey items include a variety of voles including heather voles, Red Tree Voles, meadow voles, montane voles, and red-backed voles. A study of roosting habits and winter food located in north-central Washington found that Northern Saw-whet Owls feed primarily on Western Harvest Mice and deer mice (Grove, 1985).
Northern Saw-whet Owls will also eat an assortment of small birds including juncos, sparrows, chickadees, kinglets, and swallows (Devine & Smith, 2005). They are capable of killing larger birds such as the Rock Pigeon and Northern Cardinal (Lewis, 2015). Insects and frogs may also be included in their diets as well as pocket gophers and squirrels (Cornell Lab of Ornithology, Lewis, 2015). The diet of Northern Saw-whet Owls, like other owls, is easily determined as they regurgitate the skulls, claws, teeth, and feathers of any animal they ingest.
Northern Saw-whet Owls hunt mostly at night and early in the morning using the tactic of sitting and waiting on low perches to drop down onto their prey, on the ground. They also hunt in heavy shrub and wooded areas. An owl may kill up to 6 mice during a plentiful prey season without feasting on any of them (Lewis, 2015). nstead, Northern Saw-whet Owls will cache some of their prey. Caching is the action of hiding prey or storing it somewhere else to save it for later. Owls place their prey across twigs, branches, and even under dirt or other debris. During the winter months in Connecticut, Devine and Smith (2005) observed 16 instances of caching. They noticed that Northern Saw-whet Owls usually keep their prey within 5 cm of them while roosting.
At just 8 inches in length, the Northern Saw-whet Owl is one of the smallest owl species in North America. Like most owls, this species possesses short legs, rounded wings, large yellow eyes, and a disk-shaped face. Apart from its small size, it may best be identified by its coloration, which is brown spotted with white above and white streaked with brown below and on the face. The Northern Saw-whet Owl breeds primarily in Southern Canada and the northern tier of the United States. Breeding populations also exist at higher elevations in the western U.S. and in the Blue Ridge and Great Smoky Mountains in the southeast. During winter, this species expands its range southward and into lower elevations, including the coastal southeast, the Great Plains, and the southwest. The Northern Saw-whet Owl inhabits forests across the northern part of the continent, and each geographic region in which this species may be found has forests with a different mix of trees. Regardless of the exact species present, this owl prefers forests that are composed either entirely of evergreen trees or of a mix of evergreen and deciduous tree species. In winter, individuals which move outside the species’ breeding range are less tied to a particular habitat type, relocating as new sources of prey become available. Like most owls, the Northern Saw-whet Owl hunts small mammals, including mice, shrews, and voles. This owl uses its excellent hearing to locate prey on the ground in order to fly down and capture it with its talons. Also, like most owls, this species hunts almost exclusively at night, making it difficult to observe. Northern Saw-whet Owls are most visible roosting high in trees during the day or while producing toot-like calls at dusk.
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 who was 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 the ventral side of the wing, the feathers will fluoresce a neon pink. This is used in order to estimate molt and age in adult northern saw-whet owls.[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 acadicus acadicus 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]
Their 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.
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.[26] 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.[27] This is due to loss of boreal forests from hemlock woolly adelgid, logging, and pollution.[27]
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.[28][29] 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.[30] 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).[31] A similar study by Holt and Leroux (1996) in Montana found saw-whet owls eating more voles (60%) than other mammal species.[32] 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).[33]
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 pigeon (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.
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.[34] Rocky gained more fame when Frontier Airlines announced that her image will be featured on the aircraft tails in their fleet.[35]
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.
