The boreal owl ( Aegolius funereus) or Tengmalm's owl is a small owl in the "true owl" family Strigidae. It is known as the boreal owl in North America and as Tengmalm's owl in Europe after Swedish naturalist Peter Gustaf Tengmalm or, more rarely, Richardson's owl after Sir John Richardson.
Due to the boreal owl's shyness and evasive reaction to human activities, Nocturnality and preferred inaccessible taiga forest habitat, it is rarely seen by humans.
Taxonomy
The boreal owl was formally described by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae. Linnaeus placed it with all the other owls in the genus Strix and coined the binomial name Strix funerea.
Related species
Congeners include northern saw-whet owl ( A. acadicus), unspotted saw-whet owl ( A. ridgwayi), and buff-fronted owl ( A. harrisii), all found in the New World.
Subspecies
Seven subspecies are recognized:
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A.f. richardsoni (Bonaparte, 1838) – Alaska, north Canada and north United States
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A.f funereus (Carl Linnaeus, 1758) – nominate subspecies, from Scandinavia down south to the Pyrenees and east to the Urals, but not the Caucasus Mountains
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A.f. magnus (Sergei Buturlin, 1907) – northeast Siberia
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A.f. sibiricus (Buturlin, 1910) – southeast and south Siberia
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A.f. pallens (Herman Schalow, 1908) – west and central Siberia
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A.f. caucasicus (Buturlin, 1907) – Caucasus Mountains
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A.f. beickianus Erwin Stresemann, 1928 – northwest India to southwest China
Fossil History
Remains of the boreal owl dating back to the Pleistocene were found in a cave in southern New Mexico.
Description
The boreal owl is small with a large head and long wings. Both sexes are similar in appearance, though females are larger. Males typically measure 21–25 cm (8.3-9.8 in) in length, with a wingspan of 55–58 cm (21.7-22.8 in), while females are larger – 25–28 cm (9.8–11 in) – with a wingspan of 59–62 cm (23.2-24.4 in). A female is heavier than a male bird and weighs 132-215 g (4.7-7.6 oz) compared to 93-139 g (3.3-4.9 oz) for a male bird.
Adult identification
The plumage is brown above, with white flecking on the shoulders and whitish underparts with rust-colored streaks. Its large head has yellow eyes and an olive-brown crown with small white droplets and larger central spots. The dull white facial disc is framed with a dark border and white "eyebrows" often described as giving the owl a "surprised" expression. The underparts are cream-white with russet-brown streaks, while the tail has olive-brown feathers with narrow bars. are dark olive-brown with contrasting white spots. The primaries typically have up to five rows of white spots, while the tail has three distinct rows of spots.
Juvenile identification
Juvenile boreal owls, at about 3 weeks old, have a completely dull, chocolate-brown upperparts and underparts, with a dark brown facial disc bordered by black and white markings near the bill. Upon Fledge, their plumage remains similar but with white markings on the neck, scapulars, flight feathers, and tail. They develop a broad white "X" between the eyes and distinct white streaks along the face, with cream-colored belly and flanks streaked in dark gray-brown.
Moults
Boreal Owls have two primary moulting phases. The Prebasic I molt occurs around the age of two months, between August and September. It only affects the head, body, and wing coverts. The flight feathers, tertials, greater primary coverts, and tail are unaffected.
Vocalizations
Vocalizations and related functions can be challenging to interpret because of their nocturnal and evasive lifestyle. Starting at one week old, young owls produce a harsh "peep" or "chirp" that softens after fledging. Comprehensive studies in North America has found 8 different types of vocalizations that play an important role in communication, mating, and territorial behaviour:[Meehan, R. H. (1980). Behavioral significance of Boreal Owl vocalizations during breeding season. Master's Thesis, Univ. Alaska, Fairbanks.]
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The Primary Song - loud trill sung by males to attract females and establish territory
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The Prolonged Song - softer courtship melody sung by males from beginning of courtship to incubation to strengthen bonds
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The Delivery Call - soft call by male to signal the transfer of prey to a female or young
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The Screech - a load contact call made while flying or from a perch
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The Peeping Call - soft vocalization by females throughout breeding to respond to males' calls
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The Weak Call - single note repeated rapidly from females in nest after hatching
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The Chuuk Call - harsh response call by females on male's territory
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The Hiss Call - defensive call by females when the nest is disturbed
Bill clapping is used as a protective sound by both adults and juveniles, and is frequently associated with vocal hiss. Young develop bill clapping at least one week before fledging. Adults reply with a bill clap when humans handle them or enter the nest cavity.
Calls are similar in sound to the "winnowing" of the North American Wilson's snipe.[Alaska Department of Fish and Game The Boreal Owl. [1], Retrieved on May 10, 2013.]
Distribution and habitat
The boreal owl breeds in dense boreal, subalpine forest as well as mixed woodland. The preferred habitats are old-growth forests as they provide shelter from avian predators and an abundant number of preys.
Behaviour
Breeding
Boreal owls are Monogamy and raise a single brood once they reach one year of age. The breeding begins with a lengthy courtship process where males sing for up to 102 days, starting from mid-February to mid-April, depending on environmental factors like prey availability and weather.[Korpimaki, E. (1981). On the ecology and biology of Tengmalm's Owl ( Aegolius funereus) in southern Ostrobothnia and Suomenselka, western Finland. Acta Univ. Ouluensis A 118 Biol. 13:1-84] The clutch is usually 3-7 eggs which are laid at 2-day intervals. They are glossy white and measure and weigh around . The eggs are incubated only by the female beginning with the second egg and incubation lasts on average 29 days for the first egg and 2.6 days less for the last one.[März, R. (1968). Der Rauhfusskauz. Wittenberg-Lutherstadt: Die Neue Brehm-Bücherei 394.
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[Joneniaux, A. and G. Durand. (1987). Forest management and population ecology of Tengmalm's Owl. Rev. Ecol. Terre et la Vie, Supl. 4:84-87]
Food and feeding behaviour
This small owl eats mainly and other (such as mice, , other , , moles, and ),
Threats
Biological resource use - timber harvest
Logging activities have a negative impact on prey availability, foraging efficiency and suitable nesting sites.
Predation
Marten species (Martes spp.) and Tawny owl are the predominant predators of boreal owl owlets and adult females at nest locations, with martens preying on 48% of Norwegian clutches.
Mortality
Boreal owl mortality rates vary by region and age. In Idaho, adult annual survival rate was 46%,
Conservation status
The current population trend is stable with 730,000 - 1,810,000 mature individuals: the species is currently listed under Least Concerned under CITES Appendix II, the EU Birds Directive Appendix I, and Raptors MOU Category 3.
Sources
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