Northern Saw-whet Owl

Aegolius acadicus

Taxonomy:
Class: Aves
Order: Strigiformes
Family: Strigidae
Subfamily: Striginae
Genus: Aegolius

Length: 7-8 in.
Weight: 2.5-4 oz. (females slightly larger than males)
Wingspan: 18-21 in.

Common Names: acadian owl, farmland owl, sparrow owl, Queen Charlotte owl

Etymology: aigolos (Greek) - "a nocturnal bird of prey"; acadicus - a Latinism, "of Acadia," a French colony of southeastern Canada

Description: One of the smallest northern owls (the northern pygmy-owl is smaller), saw-whet owls have large, round heads without ear tufts; their facial disk is round. Saw-whet upper-parts are brown and streaked with white on crown, with white spots on the back, wings, and tail. Their facial disk is white between yellow/golden eyes. Saw-whets have short legs that are heavily feathered to the talons. Juvenile owls lack the white markings and have an unmarked brown breast and buff belly, and conspicuous Y-shaped white markings between and above the eyes.

Flight: Flies low to the ground with rapid wingbeats and great maneuverability, often in a woodpecker-like bounding flight, swooping up to perches.

Voice: The main saw-whet vocalization sounds like a mill saw being sharpened. They have about nine different vocalizations; the one considered sounding like a saw is described as a short series of loud, sharp, squeaking calls (e.g., ksew-ksew-ksew) given by both sexes.

Habitat: This owl prefers dense forest for roosting. It is common in open ponderosa pine forests and often breeds in riparian woodland in shrub-steppe environments, foraging there in sagebrush and antelope brush habitats. In Idaho, it avoids dense Douglas fir and prefers riparian and savanna habitats.

Distribution: They are present year-round on breeding range, but considerable numbers move south in autumn, at least in eastern North America. Saw-whet owls migrate throughout the night, and on average females migrate earlier in the season than males.

Nesting: Saw-whet owls are normally monogamous, but there is no known instance of pair bond lasting more than one season, and polygamy can occur when prey is abundant. Nesting duties are strictly divided; males provide almost all of the food for the female and young while females incubate the eggs and brood the young. Although no positive evidence exists, females are likely sequentially polyandrous at times, leaving their first male to raise the first brood while mating with a second male to raise a second brood. Saw-whets are cavity nesters, using existing woodpecker nest cavities and also nest boxes. Their eggs are laid directly on wood chips or other debris, and they do not reuse nest due to prey remains. Clutch size is usually 5-6 eggs and the incubation period lasts 27-29 days. Young are about 18 days old when the female starts to roost elsewhere.

Food: Saw-whets hunt almost entirely at night from perches on low branches, shrubs, or fence posts, usually in forest openings and other habitat edges. These owls detect prey with excellent hearing and by low-light vision. Major food items are woodland mice and voles. Their diet also includes shrews, pocket mice, harvest mice, and juveniles of pocket gophers, chipmunks, squirrels. Since only half of any prey item is usually eaten at once, food not eaten immediately is often stored on branches. Prey frozen in this situation is thawed before eating by placing it in an incubation position. Males often bring an excess of food to the nest, especially during egg laying; as many as 24 surplus prey items can be found around the incubating female at this time.