Boreal Owl

Least Concern

Aegolius funereus

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About

The Boreal Owl, also known as Tengmalm's Owl in Europe, is a small, nocturnal owl of the northern forests. It is characterized by its relatively large head, short tail, and distinctive facial disc. It is a cryptic species, often difficult to detect due to its nocturnal habits and preference for dense coniferous forests.

Size & lifespan

Length: 22-27 cm (8.7-10.6 in)
Wingspan: 50-62 cm (20-24 in)
Weight: 90-215 g (3.2-7.6 oz)
Lifespan: Up to 10 years in the wild, though typically shorter.
Diet: Carnivore, primarily preying on small mammals (voles, shrews, mice) and occasionally small birds and insects.

Physical characteristics

Plumage: Adults have dark brown upperparts heavily spotted with white, and whitish underparts streaked with brown. The facial disc is whitish to grayish-white, bordered by dark brown, giving a surprised or stern expression. The crown is spotted with white. Flight feathers and tail are barred with white.
Beak shape: Small, hooked, yellowish-horn colored beak, mostly concealed by facial feathers.
Eye color: Bright yellow eyes.
Leg color: Feathered legs and feet, typically grayish-brown.
Distinguishing features: Large, round head without ear tufts; prominent whitish facial disc outlined in dark brown; small size; heavily spotted brown upperparts; bright yellow eyes.
Juvenile appearance: Juveniles are uniformly dark chocolate brown on the head and upperparts, with a dark facial disc and a prominent white 'eyebrow' or supercilium. Underparts are also dark brown. They lack the white spotting of adults. This plumage is retained for their first summer.
Seasonal changes: No significant seasonal plumage changes. Plumage remains consistent year-round for adults.
Sexual dimorphism: Females are generally slightly larger and heavier than males, but plumage is identical.

How to identify

1
Size and Shape
Small, compact owl with a relatively large, round head and no ear tufts. Short tail.
2
Facial Disc
Prominent whitish to grayish-white facial disc, distinctly outlined in dark brown, giving a 'surprised' or 'stern' expression. This is a key field mark.
3
Eyes
Bright yellow eyes, contrasting with the facial disc.
4
Plumage Pattern
Dark brown upperparts heavily spotted with white. Whitish underparts streaked with brown. Crown is spotted, not streaked.
5
Vocalization
Listen for the male's distinctive, rapid series of soft, flute-like hoots ('poo-poo-poo-poo-poo') during late winter and early spring nights.
6
Habitat
Look in dense, mature coniferous or mixed forests, especially near clearings or wetlands, and areas with old woodpecker holes.

Habitat & range

Biomes: Boreal forests, taiga, subalpine coniferous forests.
Geographic range: Holarctic distribution, found across the boreal forest zones of North America (Alaska, Canada, northern contiguous US states) and Eurasia (Scandinavia, Russia, Siberia, Central Europe, Himalayas).
Elevation range: Typically found from sea level up to 2,000 meters (6,500 feet), occasionally higher in mountainous regions.
Preferred environments: Dense, mature coniferous or mixed coniferous-deciduous forests, often near clearings or wetlands. Requires old-growth forests with abundant tree cavities for nesting.

Behavior

Activity time: Nocturnal, but can be active at dusk and dawn (crepuscular).
Feeding habits: Primarily a nocturnal hunter, but can be crepuscular, especially during breeding season or in northern latitudes with long daylight hours. Hunts from a perch, swooping down silently to capture prey on the ground or in snow. Excellent hearing allows it to locate prey under snow.
Social behavior: Solitary outside of the breeding season. Pairs form for breeding and are monogamous for at least one season.
Flight pattern: Silent, undulating flight with rapid wing beats followed by glides. Often flies low through the forest understory.
Migration pattern: Generally resident throughout its range, but irruptive movements can occur in response to prey scarcity (especially voles). Northern populations may move south in winter during such events.
Territoriality: Males establish and defend territories, primarily through vocalizations, especially during the breeding season.

Song & calls

Song: The male's primary song is a rapid series of soft, hollow, flute-like hoots, 'poo-poo-poo-poo-poo', typically 5-8 notes per second, often accelerating and increasing in volume. It can be heard from a considerable distance.
Call: Various calls include a sharp 'skiew' alarm call, a 'kewick' contact call, and a soft 'chup' call by the female near the nest. Young birds make begging calls.
When they vocalize: Most vocal during the breeding season (late winter to early spring), primarily at night, but also at dusk and dawn.

Breeding & reproduction

Breeding season: Typically March to June, with peak egg-laying in April-May, depending on latitude and food availability.
Nesting habits: Obligate cavity nester, almost exclusively using old woodpecker (especially Black Woodpecker or Pileated Woodpecker) holes or natural tree cavities. Will also use artificial nest boxes. Nests are typically in large, old trees.
Clutch size: 3-7 eggs, but can be up to 10-11 in years of abundant prey (vole irruptions).
Egg description: White, smooth, and unspotted. Roughly spherical.
Incubation period: 25-32 days, primarily by the female.
Fledging period: Young leave the nest cavity at about 28-36 days old, but remain dependent on parents for several weeks thereafter.
Parental care: Female incubates and broods, while the male provides all food for the female and young during incubation and early nestling stages. Both parents feed the young after they fledge.

Where to find

Mature Coniferous Forests

Focus on areas with old-growth spruce, fir, and pine, particularly those with standing dead trees or snags suitable for nesting cavities.

Forest Edges and Clearings

They often hunt along the edges of forests, clearings, or bogs where prey is more accessible.

Mountainous Regions

In some parts of its range, it can be found in subalpine forests at higher elevations.

Field tips

Listen at Night. The Boreal Owl is primarily nocturnal. The best chance to detect them is by listening for the male's distinctive hooting song during late winter and early spring nights, especially on calm, clear evenings.
Look for Pellets. Check the base of large trees, especially those with potential cavities, for owl pellets (regurgitated indigestible prey remains). This can indicate owl presence.
Scan Tree Cavities. During the day, carefully scan old woodpecker holes or natural tree cavities, as they are obligate cavity nesters and may be roosting inside.
Irruption Years. During irruption years (when prey populations crash in their northern range), Boreal Owls may move south into areas where they are not typically found, increasing chances of observation.
Use Playback (with caution). Using call playback can sometimes elicit a response, but should be used sparingly and responsibly to avoid disturbing the birds, especially during breeding season.

Similar species

Northern Saw-whet Owl

Aegolius acadicus

The Northern Saw-whet Owl is smaller, has a more reddish-brown plumage, and lacks the prominent dark border around the facial disc. Its facial disc is less distinctly outlined, and its crown is streaked, not spotted. The Boreal Owl's facial disc is whiter and more defined, giving it a 'surprised' look, and its overall coloration is grayer-brown.

Great Gray Owl

Strix nebulosa

While both inhabit boreal forests, the Great Gray Owl is vastly larger (the largest owl in North America by length) and has a much larger, grayer facial disc with concentric rings and a prominent 'bow-tie' pattern under its beak. The Boreal Owl is tiny in comparison.

Pygmy Owls (e.g., Eurasian Pygmy Owl)

Glaucidium passerinum

Pygmy owls are much smaller, have a more compact body, and typically have 'false eyes' on the back of their head. Their flight is more direct and less undulating. Boreal Owls are larger, lack false eyes, and have a distinct facial disc.

Quick facts

Diet:: Small mammals (voles, shrews)
Habitat:: Boreal and subalpine coniferous forests
Activity:: Nocturnal/Crepuscular
Nesting:: Tree cavities (old woodpecker holes)
Conservation Status:: Least Concern
Distinguishing Feature:: White facial disc with dark border, no ear tufts

Fun facts

The Boreal Owl has exceptional hearing, allowing it to locate and capture prey moving under several inches of snow, even in complete darkness.
Its European common name, Tengmalm's Owl, honors Swedish naturalist Peter Gustaf Tengmalm.
Boreal Owls are known for their 'irruptive' movements, where large numbers may move south from their typical range during winters when their primary prey (voles) are scarce.
Despite being widespread, they are considered one of the most difficult owls to find due to their nocturnal habits, cryptic plumage, and preference for dense forests.
The number of eggs laid by a female Boreal Owl can vary dramatically depending on the abundance of prey, with larger clutches in 'good' vole years.

Scientific classification

Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Strigiformes
Family: Strigidae
Genus: Aegolius
Species: Aegolius funereus

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