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Aegolius funereusboreal owl(Also: Tengmalm's owl/boreal owl)

By Dave Konopka

Geographic Range

Aegolius funereus can be found in subalpine and boreal forests across the northern hemisphere, including the Neartic and Palearctic regions of the globe. Its range generally follows the northern forest belt. ("Tengmalm's Owl", 1980; Hayward and Hayward, 1992; Johnsgard, 1988; Lewis, 2005)

In North America, where they are known as boreal owls, the range extends from Alaska to eastern Canada. ("Tengmalm's Owl", 1980; Hayward and Hayward, 1992; Johnsgard, 1988; Lewis, 2005)

In Eurasia A. funereus is called Tengmalm’s owl. In Europe they are found mostly in Scandinavia, though there are several scattered populations also found in subalpine forests in the central mountain regions. The range of Tengmalm’s owls extends eastward from Scandinavia, stretching across virtually all of northern Siberia, as they inhabit the taiga lowlands. Their range dips south as it approaches the Pacific Ocean, occurring throughout forested mountains north of the Korean Peninsula. ("Tengmalm's Owl", 1980; Hayward and Hayward, 1992; Johnsgard, 1988; Lewis, 2005)

Habitat

Aegolius funereus occur almost exclusively in coniferous forests. However, they are also found in areas of deciduous forest. Dominant tree species in these forests include Engelmann spruce, black spruce, white spruce, aspen, poplar, birch, and balsam fir. They are usually found in dense forests, they seem to avoid areas that are more exposed. ("Tengmalm's Owl", 1980; Hayward and Hayward, 1992; Johnsgard, 1988)

In North America, boreal owls are found from 1580 m to over 3200 m. They occur as low as 1100 m in Central Europe and as high as 2000 m in Siberia. However, during extreme weather, Tengmalm’s owls have been observed as low as 400 m. ("Tengmalm's Owl", 1980; Hayward and Hayward, 1992; Johnsgard, 1988; Lewis, 2005)

  • Range elevation
    400 to >3200 m
    1312.34 to ft

Physical Description

Aegolius funereus individuals are small owls with large, rectangular heads and long wings. Males are typically between 21 and 25 cm in length, while females are slightly larger, being between 25 and 28 cm. Like most owls, they have an obvious, light colored facial disc. The head is covered in brown and black mottled feathers. The bill is whitish-yellow, in contrast to the black bill of the northern saw-whet owl. The underparts are white, while the back and wings are predominantly dark brown with lighter spots. The legs are covered in white feathers to the claws. Aegolius funereus is unique from all other owls in that, when the tail is closely folded, there are 3 rows of white spots visible on the dorsal surface. Females are larger than males, weighing 132 to 215 grams, while males weight from 93 to 139 grams. Wing spans are between 55 and 58 cm in males and between 59 and 62 cm in females. ("Tengmalm's Owl", 1980; Hayward and Hayward, 1992; Johnsgard, 1988; Lewis, 2005; Owling.com, 2001)

Young are similar in appearance to adults, with more muted colors. ("Tengmalm's Owl", 1980; Hayward and Hayward, 1992; Johnsgard, 1988; Lewis, 2005; Owling.com, 2001)

  • Sexual Dimorphism
  • female larger
  • Range mass
    93 to 215 g
    3.28 to 7.58 oz
  • Range length
    21 to 28 cm
    8.27 to 11.02 in
  • Range wingspan
    55 to 62 cm
    21.65 to 24.41 in

Reproduction

Aegolius funereus is primarily monogamous. However, there have been documented cases of both bigyny (one male with two mates) and biandry (one female producing two clutches by two different mates). These cases have been observed only in Eurasia, and only when food is extremely plentiful. Males don't defend large foraging territories, but rather nest sites (old woodpecker holes), which are often in short supply. Fights between males have not been observed, and it appears that they compete for females through song and flight. Males will fly between perches near females, and sing a courtship song to attract female interest. If a female is interested, she will inspect the nest and, if she accepts it, she will simply stay there. The courtship period might last anywhere from 2 to 6 weeks for individual owls and from 1 to 4 months for the population as a whole. ("Tengmalm's Owl", 1980; Hayward and Hayward, 1992; Johnsgard, 1988)

Breeding season is variable, but takes place most commonly from March to June. Clutch size varies with food availability, but is typically around 4 or 5. Eggs are laid once every two days and brooding begins with the first egg, so hatching is asynchronous. Incubation is typically 28 days long. Young fledge about 30 to 31 days after hatching. The young are cared for by their parents for about a 6 weeks after fledging before setting out on their own. They become sexually mature in their first year, at around nine months old. ("Tengmalm's Owl", 1980; Hayward and Hayward, 1992; Johnsgard, 1988; Lewis, 2005; Owling.com, 2001)

  • Breeding interval
    Boreal owls typically breed once yearly. If food is plentiful then multiple clutches may occur.
  • Breeding season
    Breeding season is highly variable, but is typically from the end of February to as late as July.
  • Range eggs per season
    2 to 7
  • Average eggs per season
    5
  • Average eggs per season
    5
    AnAge
  • Range time to hatching
    25 to 32 days
  • Range fledging age
    28 to 36 days
  • Range time to independence
    6 to 7 weeks
  • Range age at sexual or reproductive maturity (female)
    9 to 9 months
  • Range age at sexual or reproductive maturity (male)
    9 to 9 months

Boreal owls provide considerable care for their young, both before and after hatching. Females stay near the nest about a week before egg laying. During this pre-fertilization time, males hunt for themselves and bring food back to their mate. After the clutch has been laid, males continue to provide food for females, but otherwise stay away from the nest. Females incubate the eggs, leaving once daily to eliminate waste. After hatching, males bring food for females and nestlings. Females tear food into smaller pieces that the nestlings can swallow, until they become big enough to eat prey whole. Brooding occurs as long as there is still young in the nest. The final young typically fledges after about 4 weeks from the start of incubation. Once the young have fledged, they stay close to the nest site for about a week, and both parents bring food to them at night, homing in on the begging calls of the fledglings. At the end of the week, the fledglings begin to move farther away, but are still fed for some time by the parents. They finally become independent about six to seven weeks after hatching. ("Tengmalm's Owl", 1980; Hayward and Hayward, 1992; Johnsgard, 1988; Lewis, 2005; Owling.com, 2001)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • male
      • female
  • pre-hatching/birth
    • provisioning
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • male
    • protecting
      • female
  • pre-independence
    • provisioning
      • male
      • female
    • protecting
      • male
      • female

Lifespan/Longevity

The longest known lifespan for a boreal owl is 16 years, from several banded individuals in various studies. In Finland, a study was done to determine the survival rate of A. funereus. Only 50% of first year males survived, while 67% of adult males survived annually. Other studies have put adult survival at 72% and 62% respectively. Yet another study determined that 78% of fledgling males died before they reached sexual maturity. (Hayward and Hayward, 1992; Owling.com, 2001)

Behavior

Aegolius funereus individuals are solitary and active almost exclusively at night, as well as periodically at dawn and dusk. They interact with conspecifics only during the breeding season. They are considered migratory, as some populations make small scale movements seasonally, but are primarily sedentary. They are dependent upon trees and forested habitats for all aspects of their life; they roost, nest, and use tree perches as a vantage point from which to hunt. Males are territorial, but typically only during breeding season, and only in the immediate area of the nest. Members of this species avoid each other when not in breeding season, with non-overlapping ranges spaced a couple hundred meters from each other.

The Boreal Owl flies most often by beating its wings rapidly, but it is also capable of gliding. It has even been observed hovering for a few seconds at a time. ("Tengmalm's Owl", 1980; Hayward and Hayward, 1992; Johnsgard, 1988; "Tengmalm's Owl", 1980; Hayward and Hayward, 1992; Johnsgard, 1988)

  • Range territory size
    1 to 5 km^2

Home Range

An individual may travel several kilometers during a foraging period. The distance between roosts can be as great as 7000 meters, though between 1000 and 1500 meters is more typical. (Hayward and Hayward, 1992; Hayward and Hayward, 1992; Johnsgard, 1988)

Communication and Perception

Boreal owls are solitary animals, and do not communicate often with other boreal owls except during the breeding season. In order to attract a mate, a male will sing and also making flying passes past females. After leaving the nest, young will call out to their parents with a begging call when they are hungry. Other calls include a warning call used by both sexes as well as a call used by the male to let the female know he has brought food to the nest. Boreal owls will also snap their bill together as a warning when they feel threatened. ("Tengmalm's Owl", 1980; Hayward and Hayward, 1992; Johnsgard, 1988; Lewis, 2005)

Boreal owls perceive their environment visually, acoustically, and chemically. They have keen eyesight, especially in the dark, and can detect prey by prey-generated sounds. Boreal owls, like most owls, have an asymmetrical external ear structure that makes it possible for them to precisely locate prey using only prey-generated sounds. They can hunt for prey completely hidden under snow cover. ("Tengmalm's Owl", 1980; Hayward and Hayward, 1992; Johnsgard, 1988; Lewis, 2005)

Food Habits

Boreal owls are carnivorous. They feed primarily on small mammals, such as voles, mice, chipmunks, and squirrels. In North America, they have been observed preying on red-backed voles (Myodes gapperi), heather voles (Phenacomys intermedius), jumping mice (Zapus), northern pocket gophers (Thomomys talpoides, and northern flying squirrels (Glaucomys sabrinus). Boreal owls have also been hunting insects and small birds, such as dark-eyed juncos (Junco hyemalis), American robin (Turdus migratorius), and common redpolls (Carduelis flammea). Females may prefer larger, mammalian prey and males may specialize on hunting smaller mammals and birds. During the winter and breeding season boreal owls cache food in rock crevices or tree branches. ("Tengmalm's Owl", 1980; Hayward and Hayward, 1992; Johnsgard, 1988; Lewis, 2005; Owling.com, 2001)

When hunting, boreal owls sit on a perch and wait for prey to scamper into sight. They usually select a perch that is bare below, but provides good cover overhead, so that it is more difficult for predators to spot them. Once they have spotted prey, they descend slowly, grasp the prey with their claws, bracing themselves against the ground for leverage. They kill prey with a quick bite to the head or neck. Boreal owls typically eat prey on a perch. ("Tengmalm's Owl", 1980; Hayward and Hayward, 1992; Johnsgard, 1988; Lewis, 2005; Owling.com, 2001)

  • Primary Diet
  • carnivore
    • eats terrestrial vertebrates
  • Animal Foods
  • birds
  • mammals
  • insects

Predation

The primary predators of adult and fledgling boreal owls are other owls and hawks. Included in these are: Accipiter cooperi (Cooper's hawks), A. gentiles (northern goshawks), Buteo virginianus (great horned owls), Strix uralensis (Ural owls), and Strix aluco (tawny owls). All of these predators hunt boreal owls from the air. When they sense a predator nearby, boreal owls will shrink away into a concealment position, remaining motionless and as small as possible to prevent from being seen.

Martens (Martes) are the primary predators of eggs, owlets, and adult females in the nest. Red squirrels (Tamiasciurus hudsonicus) are also probable egg predators. (Hayward and Hayward, 1992)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Boreal owls are thought to be one of the most important avian predators of small mammals, such as voles and mice, throughout their range. More than 90% of their diet comes from this source. They are also, as noted above, a prey animal for several other species. (Hayward and Hayward, 1992; Johnsgard, 1988)

Economic Importance for Humans: Positive

Aegolius funereus has very little impact on humans, aside from its role as a predator of small mammals which humans might consider pests.

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

There are no known adverse effects of A. funereus on humans.

Conservation Status

Aegolius funereus is not endangered. They are rarely hunted by humans because of their small size. Further, humans don’t kill its prey, so it has a fairly stable food source. The only real impact made by humans on the species is destruction of habitat by harvesting trees for lumber. Nest boxes are sometimes placed on trees to provide nest sites. Since boreal owls are considered migratory, they are protected by the US Migratory Bird Act. (Hayward and Hayward, 1992; Johnsgard, 1988)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Dave Konopka (author), Kalamazoo College, Ann Fraser (editor, instructor), Kalamazoo College.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

holarctic

a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

World Map

Found in northern North America and northern Europe or Asia.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

tactile

uses touch to communicate

taiga

Coniferous or boreal forest, located in a band across northern North America, Europe, and Asia. This terrestrial biome also occurs at high elevations. Long, cold winters and short, wet summers. Few species of trees are present; these are primarily conifers that grow in dense stands with little undergrowth. Some deciduous trees also may be present.

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

visual

uses sight to communicate

References

1980. Tengmalm's Owl. Pp. 606-616 in S Cramp, ed. Handbook of the birds or Europe, the Middle East and North Africa: the birds of the Western Palearctic, Vol. 4. New York: Oxford University Press.

Hayward, G., P. Hayward. 1992. Boreal Owl. The Birds of North America, 2: 1-16.

Johnsgard, P. 1988. North American Owls. Washington, D.C.: Smithsonian Institution Press.

Lewis, D. 2005. "Boreal Owl - Aegolius funereus " (On-line). The Owl Pages. Accessed October 07, 2005 at http://www.owlpages.com/owls.php?genus=Aegolius&species=funereus.

Owling.com, 2001. "Boreal Owl Biology" (On-line). Owling.com. Accessed October 07, 2005 at http://www.owling.com/Boreal_nh.htm.

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