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.[3][4]
Due to the boreal owl's shyness and evasive reaction to human activities, nocturnal habits and preferred inaccessible taiga forest habitat, it is rarely seen by humans.
The boreal owl is 22–27 cm (8.7–10.6 in) in length and has a wingspan of 50–62 cm (20–24 in).[9] A female is heavier than a male bird and weighs 131–179 g (4.6–6.3 oz) compared with an average of 107 g (3.8 oz) for a male bird.[10] The plumage is brown above, with white flecking on the shoulders and whitish underparts with rust-colored streaks. The head is large with yellow eyes and a dull white facial disc that is sometimes described as giving the owl a "surprised" expression. The beak is a light yellow, rather than dark like its relative the northern saw-whet owl.[11] The ears are asymmetrical in multiple bones, which affects their hunting success. The sexes are similar in appearance. The plumage of young birds is chocolate brown. The boreal owl's flight is relatively noiseless and straight.[9]
Its call is similar in sound to the "winnowing" of the North American Wilson's snipe.[12][13]
The boreal owl breeds in dense coniferous forests across northern North America and the Palearctic, and in mountain ranges such as the Alps and the Rockies. This species is not normally migratory, but in some autumns significant numbers move further south. It is rarely any great distance south of its breeding range, although this is partly due to the problems of detecting this nocturnal owl outside the breeding season when it is not calling.
They first breed when one year of age. The nest is usually a hole in a tree often that made by a woodpecker, but the birds also readily use nest-boxes. The clutch is usually 3–7 eggs which are laid at 2-day intervals. They are glossy white and measure 33 mm × 26 mm (1.3 in × 1.0 in) and weigh around 12.5 g (0.44 oz). The eggs are incubated only by the female beginning with the second egg. They hatch asynchronously after 25–32 days. The young are cared for by the female who broods the nestlings for an average of 21 days. The young fledge when aged around 28–33 days and become independent at 5 to 6 weeks.[14]
Banded boreal owls have been known to live up to 16 years. Due to the owl's small stature it is often eaten by other owls and large raptors thus decreasing its average lifespan.
^ abGill, Frank; Donsker, David; Rasmussen, Pamela, eds. (January 2022). "Owls". IOC World Bird List Version 12.1. International Ornithologists' Union. Retrieved 2 March 2022.
^Jobling, James A. (2010). The Helm Dictionary of Scientific Bird Names. London: Christopher Helm. pp. 33, 166. ISBN978-1-4081-2501-4.
^ abSvensson, Lars; Mullarney, Killian; Zetterström, Dan (2009). Collins Bird Guide (2nd ed.). London: HarperCollins. p. 226. ISBN978-0-00-726814-6.
^Bull, Farrand (1994). National Audubon Society Field Guide to North American Birds: Eastern Region. New York: Alfred A. Knopf. p. 554. ISBN0-679-42852-6.
^Alaska Department of Fish and Game The Boreal Owl. [1], Retrieved on May 10, 2013.
Cramp, Stanley, ed. (1985). "Aegolius funereus Tengmalm's Owl". Handbook of the Birds of Europe the Middle East and North Africa. The Birds of the Western Palearctic. Vol. IV: Terns to Woodpeckers. Oxford: Oxford University Press. pp. 606–616. ISBN978-0-19-857507-8.
