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Saw-whet owl
Date Issued: 1978-08-26
Postage Value: 15 cents

Commemorative issue
American Owls
Saw-whet owl

The saw-whet owl is one of four owls native to the United States depicted on the set of four stamps printed together on the same pane.

Saw-whet owls are classified in the order Strigiformes, which includes typical owls and barn owls. Approximately 160 species of owls are further classified into the family Strigidae, which includes 26 genera of "typical owls." Saw-whet owls belong to one of four species in the genus Aegolius, or so-called "small forest owls." There are just two subspecies of Saw-whet owls: A. a. acadicus and A. a. brooksi.Saw-whet owls are one of the most common and widespread of North American owl species. The breeding range of the northern saw-whet owl extends from New England and the Eastern Canadian provinces across the Great Lakes region and southern Canadian plains into British Columbia. The western part of their breeding range extends from southern Alaska down through California, the southwestern states and into the mountains of Mexico. Their non-breeding range encompasses most of North America.

Northern saw-whet owls can be found in a variety of forested landscapes throughout their range including coniferous, deciduous, and even riparian woodlands in shrub steppe habitats. They prefer riparian habitats for breeding, and dense cover for roosting. They are only found in urban areas during migration. These owls rarely live at lower altitudes an appear more frequently at moderate elevations.

The saw-whet is one of the smallest species of owls. It has a large rounded head, a short tail and a relatively long wingspan. They measure 7-8.5 inches (18-22 cm) in length, with a wingspan of 17-21 inches (23-53 cm). They weigh 2.6-4.6 ounces (75-130 g), with females larger in length and weight than males.

Unlike some other owls, this species does not possess ear tufts, but instead has a prominent facial disk. Northern saw-whet owls are heavily feathered and feature complex markings. The upperparts are brown and streaked with white on the crown and nape. There are white spots on the back, tail and wings. The facial disk is white above and between the eyes and the rest is grayish brown with dark brown and white lateral streaks. The underparts are mostly white with broad brown streaks. Juveniles are dark brown on the upperparts and face, with a broad white "V" on their forehead. The breast and belly are lighter brown with few white markings. The adults have bright yellow eyes.

Life expectancy in the wild can reach 8 years, but rarely reaches more than 5 years. Most juveniles do not survive into their second year. Their life expectancy in captivity is unknown, but one captive owl lived for 16 years.

In the wild: northern saw-whet owls primarily catch woodland mice, especially deer mice. They also eat other types of mice, voles, shrews, and juveniles of small mammals such as chipmunks. They occasionally catch small birds (kinglets, wrens, sparrows, pygmy owls and others), along with insects such as grasshoppers and beetles. At the zoo: Keepers feed them small mice.

Although generally monogamous, northern saw-whet owls form pairs that last only through the breeding season. They probably don't return to a specific nest site or partner each year. The female or the pair chooses a nest in abandoned flicker and pileated woodpecker cavities. They may also nest in manmade nest boxes. Males may attract mates by singing to them from a suitable nest cavity. Sometime between March and July, the female will lay a clutch of four to seven eggs (average is five to six) at two-day intervals. The male brings food to the female, which incubates the eggs for 27-29 days. The female rarely leaves the nest during incubation.

After hatching, the female broods the young for at least another 18 days. After this, she may assist the male with feeding for up to a month thereafter. If prey is abundant and it is not too late in the breeding season, she may leave the chicks and the male to find another male and hatch another brood. The young fledge 4-5 weeks from hatching, and are thought to be fully independent between 10-13 weeks old. It is thought that they begin breeding as early as 1 year old.

Chicks fledge at 32-40 days of age and are cared by the parents and helpers for an additional 6-8 weeks. Female offspring leave their natal territory at 1-2 years of age while males disperse at 2-4 years.

Northern saw-whet owls are solitary and nomadic except during the breeding season. By day, they commonly roost on lower branches of a large tree. They often return to the same tree day after day and can be found by the resulting pile of feces. Migration patterns of the northern saw-whet owl are quite varied. The patterns range from minor local changes in location to extensive movement from northern breeding ranges to southern North America.

Northern saw-whet owls make a number of different sounds including rhythmic toots, skews, twitters, barks and whining whistles.

The saw-whet owl is nocturnal and is ideally suited for hunting in darkness. They start hunting shortly after sunset and continue until just before sunrise. As is the case with most owls, northern saw-whet owls have large eyes that are well-suited for low light or night vision. They also have exceptional hearing and are more reliant on it as a sense for locating their prey. Also like some other owl species, the saw-whet possesses asymmetrical ear openings in its skull (one opening is located higher than the other). The asymmetrical layout allows the northern saw-whet owl to more easily distinguish both vertical and horizontal sound position. Lastly, its facial disk further amplifies sound.

Saw-whets are opportunistic hunters that rely on hunting perches, such as branches and fence posts along forest edges or other open areas. The saw-whet captures prey using its strong feet and sharp talons. Each foot has four toes, and the outer toe of each foot can be rotated in a number of positions. This allows the northern saw-whet owl to maximize the strength of its grip on its prey.

Topics: Animal (529)  Bird (280)  

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