by Lisa Bate
Boreal Owls (Aegolius funereus) are one of the smaller owls found in Montana. Larger than a Northern Pygmy Owl, but smaller than a Barred Owl, they range in length from 8 to 11 inches (20 to 28 cm). Their wingspan ranges from 22 to 24 in (55 to 62 cm). They only weigh 3 to 7.5 oz (93-215 g). Like all raptor species, the females are larger than the males, yet Boreal Owls hold the distinction of the greatest sexually reversed dimorphism with the females significantly larger than the males.
Boreal Owls are a small brown owl with a large square head, yellow eyes, and a light-colored bill. They have a light-colored facial disc surrounded by a dark border. They are overall brown with underparts spotted or streaked with white. They have distinctly dark “eyebrows” and small white dots on their crown. Their legs and feet are completely feathered.
Boreal Owls are a circumpolar species, ranging across Canada and Alaska, and south into the northern parts of the U.S., and then westward into northern Siberia and Scandinavia. Their range extends in scattered pockets far south in the U.S. into subalpine forests of the Rocky and Cascade Mountains. When prey numbers are high, their home ranges are stable. If not, they are an irruptive species, moving to where prey numbers are greater.
Although Boreal Owls have been intensely studied in Scandinavia, where they are the most abundant forest owl, little is known about them in Montana. Here they are listed as a “Potential Species of Concern” because of concerns about their population size, and impacts of fire, disease, and timber harvest in the mature spruce/fir forests that they depend upon. Due to these concerns, Montana biologists have initiated statewide surveys for Boreal Owls using playback calls and automatic recording units.
The Boreal Owl scientific name comes from the word Aegolius, which is Latin meaning ‘bird of prey’ and funereus meaning ‘deadly’ indicating their reputation as a small, but deadly predator. Boreal Owls hunt mainly at night, relying on their keen hearing to determine the exact location of small rodents on the forest floor or under the snow. Their ears on either side of their heads are at different heights aiding in their ability to know exactly where their prey lies. During the day, Boreal Owls roost in trees.
Although very unusual to visibly spot Boreal Owls in Montana, their songs are distinct and allow for confirmation of this owl’s presence. Males will sing to attract a mate, singing a series of 8 to 20 low whistled toots (https://www.allaboutbirds.org/guide/Boreal_Owl/sounds). Once the female starts nesting, very little calling occurs. Getting out and listening in January through April is most ideal for hearing this otherwise secretive species.
Boreal Owls are cavity nesters relying mainly on abandoned nests made by Northern Flickers or Pileated Woodpeckers, or natural cavities. Prior to egg laying the female stays in the cavity day and night for an average of six days while the male brings her food. Boreal Owls begin nesting in late March or April, laying 2 to 6 eggs. Incubation lasts about 28 days, and the young fledge after 30 days. Boreal Owls are monogamous for only one breeding season.
Boreal Owls are uncommon and infrequently detected. So, if by chance you are lucky enough to hear or see one, be certain to report your observation to a biologist so that this information can be added to the little we know of this species.