Boreal Owl

Boreal Owl

Boreal Owl

Common Name: Boreal Owl
Also referred to as: Arctic Saw-whet Owl, Funereal Owl, Richardson’s Owl and Tengmalm’s Owl
Genus species: Aegolius funereus
Recognized subspecies: Aegolius funereus richardsoni Bonaparte and Aegolius funereus magnus Buturlin
Family: Strigidae
Order: Strigiformes

General Description:

  • Similar in appearance to the Saw-whet Owl.
  • Total length: 22 to 28 centimetres.
  • Wingspan: 55 to 62 centimetres.
  • Weight: 93 to 215 grams.
  • Tail: 88 to 107 mm.
  • Sexes appear similar, but females are slightly larger.
  • Small owl with a large head, lacking ear tufts.
  • Crown is spotted with white (rather than streaked as with the Saw-whet Owl).
  • The facial disk is grayish-white, bordered by black.
  • Iris and bill are yellow.
  • Broad ‘V’ from bill to above eyes.
  • Upper plumage is chocolate brown with white spotting.
  • Underparts are white, streaked with brown.
  • Tail is brown with narrow white bars.

 
North American Distribution

Habitat Description
Movements and Migratory Habits
Diet and Foraging Strategy
Reproduction
Conservation Status

North American Distribution:

  • Found from the tree line in central Alaska, Yukon, Nunavut, northern Saskatchewan, northern Manitoba, northern Ontario, central Quebec, and Labrador, south to southern British Columbia, central Alberta, central Saskatchewan, southern Manitoba, northern Minnesota, central Ontario, southern Quebec and New Brunswick. Also breeds locally in Washington, Idaho, Montana, Wyoming, Colorado and New Mexico.
  • In Alberta, mainly found in the Boreal Forest Natural Region, but is also found in the Rocky Mountain, Foothills and Parkland Natural Regions.

Habitat Description:

  • Home ranges are typically 1100 to 1600 hectares. There is a considerable amount of overlap of individual home ranges. Territoriality is restricted to the area immediately surrounding the nest.
  • Occupy deciduous, mixed-wood and coniferous stands in the Boreal and Subalpine forest regions.
  • Prefer mature spruce-fir forest with interspersed meadows.
  • Tend to avoid large stands of pine or quaking aspen.
  • Roost sites are typically in dense, coniferous trees, approximately 14 metres tall, with a diametre at breast height (DBH) of approximately 34 cm. Roosts approximately 5 metres above ground.
  • This species is a secondary cavity nester.

Movements and Migratory Habits:

  • Boreal Owls are nocturnal; however, diurnal activity has also been reported.
  • Typically winter on breeding home range, but are nomadic within their range in response to prey availability.
  • Similar to Great Gray Owls, Boreal Owls will make infrequent winter incursions into settled areas in response to a shortage of food.
  • These incursions peak in late winter and involve primarily non-breeding birds of both sexes. Some studies suggest that it is mostly females that display nomadic behaviours.

Diet and Foraging Strategy:

  • Primary prey is small mammals, especially voles. Voles often account for over 90% of the diet.
  • Other prey taken includes mice, tree squirrels, songbirds, bats and insects.
  • Primarily nocturnal hunters, however, hunting in daylight has also been observed.
  • Boreal Owls are sit-and-wait predators and do not actively pursue their prey.
  • Prey is located using acoustic clues. Moving prey is taken more often than stationary animals, which demonstrates the importance of auditory clues in locating prey.
  • This species has been observed diving through the snow or thick vegetation to capture prey.
  • Once captured, prey is generally consumed whole.

Reproduction:

  • The Boreal Owl is considered to be monogamous, but several cases of polygamy have been reported.
  • Pair formation occurs from mid-February to mid-April.
  • Nest in cavities with an entrance of 95 to 102 mm in diameter. These cavities may range from 3 to 17 metres above ground.
  • Breeding typically occurs in mature stands of coniferous forest.
  • Egg laying occurs in April and May.
  • Clutch size may range from 2 to 7 eggs; 4 to 6 eggs are common.
  • The dull white eggs, averaging 26 by 33 mm, are laid in 2-day intervals.
  • Incubation lasts 26 to 32 days and is done entirely by the female.
  • The male provides food for the female during incubation.
  • Hatching is asynchronous.
  • Hatchlings are altricial.
  • Brooding is done entirely by the female.
  • Fledging occurs at 28 to 36 days of age.
  • Produce a single brood per year. Replacement clutches may be laid if initial clutch is lost early.
  • Both sexes reach sexual maturity at one year.

Conservation Status:

  • Federal: Not at Risk
  • Provincial: Secure


ReferencesBoreal Owl photo © 2007 Karel Broz. Retrieved from www.istockphoto.com/stock-photo-4555462-tengmalm-s-owl.php on 18/09/09. Used with permission.

Alberta Sustainable Resource Development (ASRD). 2008. Search species and status category. <http://www.srd.gov.ab.ca/fishwildlife/speciesatrisk/statusofalbertawildspecies/search.aspx>. Accessed 17 May 2009.

Federation of Alberta Naturalists. 2007. The atlas of breeding birds of Alberta: a second look. Federation of Alberta Naturalists, Edmonton, Alberta, Canada.

Godfrey, W.E. 1986. Birds of Canada, revised edition. National Museum of Natural Sciences, Ottawa, Canada.

Government of Canada. Species at risk public registry. 2008. <http://www.sararegistry.gc.ca/sar/index/default_e.cfm>. Accessed 17 May 2009.

Hayward, G.D. and P.H. Hayward. 1993. Boreal Owl (Aegolius funereus), The Birds of North America Online (A. Poole, Ed.). <http://bna.birds.cornell.edu/bna/species/063doi:10.2173/bna.63>. Accessed 17 May 2009.

Johnsgard, P.A. 2002. North American Owls. Second edition. Smithsonian Institution Press, Washington, USA.

Lynch, W. 2007. Owls of the United States and Canada. The Johns Hopkins University Press, Baltimore, Maryland, USA.

Salt, W.R. and J.R. Salt. 1976. The birds of Alberta. Hurtig Publishers, Edmonton, Alberta, Canada.