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Northern Saw-whet Owl - Aegolius acadicus

More Northern Saw-whet Owl (Aegolius acadicus) Photos >>
 
Calls - Aegolius acadicus
Typical call © John Feith
Typical call north-western California © Bruce Marcot
Saw whetting call The call that gives this owl its name. NW Wisconsin, USA. March 2010. © Richard Peet

Introduction: The Northern Saw-whet Owl is a very small, short-bodied owl with a relatively short tail. The overly large head has no ear tufts and may appear distorted due to an asymmetrical skull. European explorers first discovered this Owl in a North American colony called Acadia (now Nova Scotia). The Latinised word acadius refers to this territory. The common name "Saw-whet" comes from these Owls unique calls described below. The Saw-whet Owl is also called Acadian Owl, Blind Owl, Kirkland's Owl, the Saw-filer, the Sawyer, Sparrow Owl, White-fronted Owl, Farmland Owl, Little Nightbird, Queen Charlotte Owl, and even the Whet-saw Owl. Common misspellings include "sawwhet" and "sawhet" owl.

[For help with terms used in the description, see parts of an owl. For general characteristics common to most owl species, see owl physiology.]

Description: The facial disc is brownish with a whitish zone around the eyes, forming radial white streaks towards the edge of the disc, and with a blackish spot between the base of the bill and the orange-yellow eyes. The bill and cere are blackish. The disc does not have a dark rim but does have a narrow edge of light and dark spots. The rest of the head is warm rusty-brown or grey-brown, and densely covered with white shaft-streaks, especially on the forehead. The mantle and the rest of the upperparts are rusty brown with white spots. Flight feathers are spotted white. The relatively short tail normally has three rows of white spots on both webs of the rectrices.
Lower parts are whitish with broad reddish-buff streaks. Toes are slightly feathered with dark horn claws with blackish tips.
Juveniles of this species are chocolate-brown above with underparts pale brownish or cinnamon-buff. The eyebrows, forehead and lores are white, forming a pale "X" on the dark face.

Size: Length 17-21.9cm. Wing length 125-146mm. Tail length 65-73mm. Weight 54-124g. Females are normally larger than males.

Habits: Northern Saw-whet Owls are strictly Nocturnal, with activity beginning at late dusk. During the day, they depend on plumage for camouflage when roosting in foliage, usually close to the ground. When threatened, a Saw-whet Owl will elongate its body in order to appear like a tree branch or bump, often bringing one wing around to the front of the body.
Flight is rapid, woodpecker-like, laboured, and undulating.

Voice: The Northern Saw-whet Owl vocalises during the breeding season only (usually between March and May). They are silent at other times of the year. The primary courtship call is a monotonous, whistled "hoop", emitted at about 1.5 notes per second which may last for several hours without a break. Territorial calls are series of short clear notes. The Saw-whet Owl's name comes from the "skiew" call that is made when alarmed. This sound has a resemblance to the whetting of a saw. When the male flies to the nest with food it gives a rapid staccato burst of toots, and the female responds with a soft "swEE".

Hunting & Food: These Owls hunt mainly at dusk and dawn and most often use the "sit and wait" tactic to drop down onto prey on the ground from low hunting perches. They will also range through wooded areas and hunt in heavy shrub cover. When prey is plentiful, a Saw-whet Owl will kill as many as 6 mice in rapid succession, without consuming any of them. The excess food is cached in safe places and, in winter, is thawed out later by "brooding" the frozen carcass. When food is plentiful, it is common for only the head of each prey to be eaten.
Northern Saw-whet Owls feed almost entirely on small mammals, Deer mice being the primary prey, followed by shrews and voles. Other mammals include squirrels, moles, bats, flying squirrels, and house mice. Small birds are sometimes taken and include swallows, sparrows, chickadees, and kinglets. Larger birds such as Northern Cardinal and Rock Dove can be killed by one of these small Owls. Frogs and insects are also part of their diet.
Pellets are very small and dark grey, about 1.9cm by 1.3cm and are ejected with great difficulty, usually with a great deal of twisting of the body and head.

Breeding: Because of their nomadic nature it is unlikely that pair bonds are permanent or that birds often return to the same nest site. Males sing their territorial song mainly in late-March and April. After a female has been attracted to a male by his song, he will fly in circles above her while calling, or he will take her directly to the nest site he has located (again, while calling). The male then lands near her and begins a complex series of bobbing and shuffling as he inches towards her. Often, the male has a mouse in its bill and offers it to the female.
Northern Saw-whet Owls nest in old woodpecker cavities, (primarily those made by Pileated Woodpeckers or Northern Flickers) or in natural cavities. They will also take to nest boxes quite readily. Nest trees are often dead and nest heights average 4 to 6 metres above ground. Nesting occurs between March and July.
Clutch sizes range from 3 to 7 eggs (average 5-6) laid at periods of 1 to 3 days, but usually 2. Eggs average 30x25 mm. The female does all incubation and the male brings food to her and defends the nesting area. The incubation period is 21 to 28 days. Young fledge at 4 to 5 weeks, and may leave the nest individually every 1 to 2 days, until they have all left. The young owls are cared for by the parents for some weeks after they leave the nest. Sexual maturity is reached at 9-10 months old.
A pair will raise a single brood; in years when food is abundant, they will nest slightly earlier in the season.

Mortality: Captive Owls have lived for over 10 years, but mortality in the wild is likely relatively high. They compete with Boreal Owls, starlings, and squirrels for nest cavities, and are preyed upon by larger Owls, martens, Cooper's Hawks, and Northern Goshawks.

Habitat: Northern Saw-whet Owls inhabit coniferous and deciduous forests, with thickets of second-growth or shrubs. They occur mainly in forests with deciduous trees, where woodpeckers create cavities for nest sites. Breeding habitat is usually swampy or wet, rather than dry. Riparian habitat is often preferred.

Distribution: North America - Breeds from south-eastern Alaska, central British Columbia, including the Queen Charlotte Islands, central Alberta, central Saskatchewan, central Manitoba, central Ontario, southern Quebec, northern New Brunswick, Prince Edward Island, and Nova Scotia, south to the mountains of southern California to southern New Mexico, locally in western South Dakota and western Minnesota, northern Illinois, southern Michigan, central Ohio, West Virginia, western Maryland, and New York; also breeds locally in the mountains of eastern Tennessee and western North Carolina.
They Winter generally throughout much of the breeding range, but part of the population migrates south regularly to the central United States and irregularly to more southern areas along the Gulf coast and central Florida.
The Northern Saw-whet Owl is highly migratory in northern and eastern areas. Two major migration corridors in eastern North America are along the Atlantic coastline and down the Ohio River valley. Juveniles are more likely to migrate than adults and tend to move further south. Migration in the fall often occurs during the passage of a cold front and during westerly winds. Southern populations move down slope during winter rather than migrating south.
The Northern Saw-whet Owl is also found in Mexico.

Distribution of Northern Saw-whet Owl - Aegolius acadicus
Distribution of the Northern Saw-whet Owl Aegolius acadicus

Status: Not threatened or endangered. Locally frequent.

Original Description: Gmelin, Johann Friedrich. 1788. Systema Naturae, 1, Pt.1, p. 296.

Subspecies: A. a. acadicus, A. a. brooksi, A. a. brodkorbi

References:

Boyer and Hume. 1991. "Owls of the World". BookSales Inc
Campbell, Wayne. 1994. "Know Your Owls". Axia Wildlife
Heintzelman, Donald S. 1984. "Guide to Owl Watching in North America". Dover Publications
König, Claus & Weick, Friedhelm. 2008. "Owls: A Guide to the Owls of the World (Second Edition)". Yale University Press
König, Weick and Becking. 1999. "Owls: A Guide to the Owls of the World". Yale University Press
Long, Kim. 1998. "Owls: A Wildlife Handbook". Johnson Books
Mikkola, Heimo. 2012. "Owls of the World: A Photographic Guide". Bloomsbury

Page Information:

Page compiled by . Page last updated 2013-06-27

OwlPages.com Owl Species ID: 230.020.000

 
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