The Northern Saw-Whet Owl is found throughout most of North America from southern Alaska and Canada to northern Mexico.
Aegolius acadicus can normally be found in dense coniferous or mixed hardwood forests; it prefers dense woods in swampy areas. It also enjoys inhabiting deciduous forests in riparian areas. In the winter, especially during times of extreme cold, or when food shortages arise, A. acadicus migrate south. During these times, they inhabit a range that goes south into Georgia and down in Mexico. Although they usually live in areas away from settlement, A. acadicus can even be found in towns and cities during some migratory periods.
One of the most striking characteristics of the Northern Saw-Whet Owl is its size - with a height of 17.8 to 21.6 cm, it is the smallest owl in eastern North America. This is also the only tiny owl east of the Rocky Mountains that does not have ear tufts. It has a dark-colored bill, eyes with yellow-pigmented irises, heavily feathered legs and feet, a tail that has three bars, and a wide, reddish-brown body with white streaks on its abdomen. Its large, round head, which is also reddish brown to brown, has a large, grayish facial disk in the center and is streaked with white on the top. Its neck is speckled with white. The Northern Saw-Whet Owl depends on this plumage for camouflage when staying in foliage. It appears larger in flight because of its broad wingspan of 45 to 60 cm. Although the sexes are similar, females are slightly larger than males. Juveniles are chocolate-brown with single large white spots above their bills that extend over their eyes.
The breeding season for Northern Saw-Whet Owls usually occurs between March and May. Once a male and female mate, they select a nesting site. These sites, which are located at heights ranging from 2 - 12 m, are usually natural cavities or abandoned woodpecker holes, often ones made by Northern Flickers and Hairy Woodpeckers. The female lays an average of 5-6 eggs at periods of 1-3 days. She does all of the incubation, which begins soon after the first egg is laid. Meanwhile, the male brings her food and defends their area. After 26-28 days, the eggs hatch. By the time they are 4-5 weeks old, the young are ready to fly. After they are a year old, they complete their first molt and grow adult plumage. They can live as long as 17 years.
During the day, A. acadicus roosts silently in dense areas of the forest. It is active at night and often has a curious nature. In the spring, these owls engage in a lengthy courtship before mating. The Northern Saw-Whet male sings a territorial song around April. When a female becomes attracted to the male's song, the male flies in circles above her head while continuing to call, then lands and performs a series of bobbing and shuffling as he nears her. He may also have a mouse, which he offers to her. Because these owls are migratory and often do not stay in one place, pairs that form are usually not permanent. Because of their small size, Northern Saw-Whet Owls are preyed upon by larger owls, martens (Martes americana), Cooper's Hawks (Accipiter cooperii), and Northern Goshawks (Accipiter gentilis). When A. acadicus feels threatened, it elongates its body to make itself look like a branch or a bump.
The Northern Saw-Whet Owl's diet primarily consists of insects and small rodents, including deer mice, rats, small squirrels, and chipmunks. It also consumes amphibians such as frogs, moles, shrew, voles, bats, and even birds and mammals as large as itself. It searches for its food at night. When Aegolius acadicus hunts, it tends to wait for its prey on low perches. It then drops down onto its prey. It may also search for food by silently floating along the edges of open parks and meadows, staying close to the ground. When it can find much prey, it may kill as many as six mice in quick succession without eating any. It does most of this hunting at dusk and dawn. The fact that A. acadius is completely nocturnal is why it preys mainly on insects and nocturnal rodents.
These owls are not known to have significant adverse affects on humans.
The Northern Saw-Whet Owl's diet helps humans. It kills many rodents, including the household pests - house mice.
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.
As in other owls, this species' wide head spaces its ear openings far apart, allowing the owl to determine the location, timing, and loudness of a sound.