Text by Eileen Dowd Stukel
Photo by Doug Backlund

Unless winter’s cold and snow keep you homebound, you’ve probably heard great horned owls calling in the woods. Their deep hoots are eerie sounds in an otherwise quiet winter landscape. While other wildlife species are content to brave this trying season, owls begin their annual breeding cycle by staking out territories and selecting nest sites.

Not far behind the common and widespread great horned owl in starting its nesting season is the diminutive northern saw-whet owl (Aegolis acadicus). Measuring only eight inches long, the male weighs the same as a robin, the female slightly more. One of its calls resembles the sound of a file sharpening the teeth of a saw; hence the name "saw-whet."

Although differing greatly in size, these two species share many characteristics. Owls have relatively large heads with large hooked bills and eyes that are oriented forward. Long toes with sharp, curved toenails help in grasping prey. Owls have a facial disc where feathers form a flat surface to help send and receive sound waves. Their feathers’ outer edges are fringed, resulting in quiet flight.

Many birds store and often soften food in their crop. Owls have no crop, so digestion begins in the gizzard. Owls don’t digest hair, feathers, or bones. Instead, these items pass to the proventriculus, called the "true stomach" in birds. These undigested parts form into small masses that the owl regurgitates as pellets. Analyzing pellets found below owl roosting spots helps us learn more about owl food habits.

The northern saw-whet owl is one of South Dakota’s seven breeding owl species. It nests primarily in the Black Hills. South Dakota is part of a widespread North American range. The northern saw-whet breeds from southern Alaska through the central Canadian provinces east to the Atlantic Coast. Its U.S. breeding range includes suitable coniferous and mixed forests of the western and northeastern states. Saw-whets frequently migrate to other areas for the winter, when it may dwell in parts of eastern South Dakota.

When early spring arrives, a male repeats a monotonous, single-noted call to advertise his territorial bounds. Saw-whet pairs are usually monogamous for the nesting season. Because of their winter wanderings, experts doubt that saw-whets mate for life. The female selects a nesting site that is typically a cavity excavated by a woodpecker, usually a northern flicker. Saw-whets also nest in nest boxes that are suitably sized and placed.

Breeding habitat varies with location, but highest breeding pair densities are found in coniferous forests that have a mixture of living and dead trees and medium-sized woodpecker-excavated cavities. The male feeds his mate typical saw-whet fare of mice, voles, and an occasional songbird. Saw-whets are nocturnal. Their asymmetrically placed ears help them detect prey under low light conditions. Saw-whets often hunt along forest edges, in forest openings, or when perched just five to 10 feet above the ground in open areas.

With only a few breast feathers as her breast lining, the female begins laying her clutch of four to seven eggs. Her mate continues in attendance, feeding her while she lays and incubates eggs and broods nestlings. When nestlings reach two to three weeks of age, the female may abandon them to the male’s care. She may then have a second brood during the same nesting season with a new mate. In times of abundant prey, male saw-whet owls may be bigamists and even trigamists, supporting two or three mates during one breeding season.

Young saw-whet owls fledge at about four weeks of age. They may stay loosely together near the nest for another month or so, where the remaining parent or parents feed them. Young saw-whets may be more likely to migrate for the winter than their parents, but prey abundance may be a deciding factor.

Saw-whets favor slightly different habitat during the nonbreeding months than they select for their nesting territory. Although found in a variety of habitats, they prefer winter roost sites with dense vegetation and foraging perches. They may appear quite tame as they perch close to coniferous tree trunks during the day. Saw-whets rarely roost in cavities or nest boxes.

What are the saw-whet owl’s conservation needs? Although fairly adaptable, this species does best in diverse, mature forests that have both living and dead trees for nesting sites and open areas for foraging. Wintering and migrating birds need areas of dense cover. Young regenerating forest stands are not favorable saw-whet habitat, since such stands are too thick and lack the open understory the birds need for foraging.

The next time you think of winter as a time of desolation and lifelessness, remember that many of South Dakota’s owls see winter as a time of renewal and the beginning of their annual struggle to find a mate and raise young.