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Boreal Owl

Aegolius funereus
Overview
Minnesota Seasonal Status:

A regular and possible permanent resident, migrant, and winter visitant. The Boreal Owl was very rare during the Minnesota Breeding Bird Atlas (MNBBA).

North American Breeding Distribution and Relative Abundance:

The Boreal Owl has a Holarctic distribution across the boreal forest of northern North America, Europe, and Asia. Its distribution in North America extends from the Maritime provinces in eastern Canada to Alaska and south in the Rocky Mountains to northern New Mexico. The species is sparsely distributed throughout its range.

Conservation Concern:
Conservation Status Score 10

Assigned a Continental Concern Score of 10/20 by Partners in Flight. The Boreal Owl is designated a species of Special Concern and a Species in Greatest Conservation Need in Minnesota. It is also a Regional Forester Sensitive Species in the Superior National Forest in Minnesota.

Life History
Migration:

A possible permanent resident in Minnesota; irruptive southward movements from northern breeding areas occur, presumably during food shortages or inclement weather.

Food:

Primarily small mammals; also birds and insects.

Nest:

A secondary-cavity nester that uses tree holes such as those previously excavated by woodpeckers.

Boreal Owl Boreal Owl. Aegolius funereus
© Mike Lentz
Minnesota Breeding Bird Distribution*

The Boreal Owl, or Richardson’s Owl as it was earlier named, was considered primarily a wintering bird in Minnesota. However, Hatch (1892) in his “First Report of the State Zoologist” for Minnesota stated, “he would not be greatly surprised if the nest is found here ultimately.” Roberts (1932), in his treatise on the birds of Minnesota, identified it only as a “rare winter visitant” and wrote that it “nests chiefly in the far north.” The single potential record of breeding activity he noted was of an individual singing near Rose Lake in Cook County near the Canadian border (Schorger 1926). This record was later disputed by Green and Janssen (1975) because the details did “not preclude the possibility of confusion with the Saw-whet Owl.”

Roberts also noted that a young bird was taken in Jefferson County, Wisconsin, in August and said it was “fair to surmise that it may yet be found nesting somewhere in the little explored wilderness just south of the Canadian boundary.” In their book on the birds of Wisconsin, Kumlien and Hollister (1903) reported this bird was collected in August 1872 in Fort Atkinson, Wisconsin.

Green and Janssen stated there were no summer records as of 1975 and noted only the potential misidentification of the species in 1926. The Boreal Owl was therefore unknown as a nesting species in Minnesota, and even in the lower 48 states, until Eckert and Savaloja (1979) found the first verified nest in May 1978 along the Gunflint Trail, Cook County. The nest hole was 0.3 m from the top of a 3.4 m black spruce stump and only 3 m from a parking area adjacent to the road. They also noted the nest was found after one of the largest winter invasions ever in the state, in 1977–78, when 66 individuals were recorded.

In 1987, Janssen reported 3 confirmed nests from Cook County, including the 1978 first nesting record (Eckert and Savaloja 1979), another in 1979 reported by Eckert (1979), and another found by Matthiae (1982) in a waterfowl nest box in Cook County. By 1998, Hertzel and Janssen (1998) had added confirmed nesting of the Boreal Owl in Lake, Roseau, and St. Louis Counties since 1970. The Minnesota Biological Survey detected 1 Boreal Owl breeding season location, which was found in central Lake County (Minnesota Department of Natural Resources 2017).

The MNBBA reported 7 records of the Boreal Owl in 4 blocks, all in central Lake County, where two MNBBA regional coordinators of that area, Dave Grosshuesch and Jim Lind, diligently looked for evidence of Boreal Owl nesting. They included 1 confirmed, 1 probable, and 2 possible records of breeding evidence (Figure 1; Table 1).

In their review of the Boreal Owl in North America, Hayward and Hayward (1993) doubted that the new breeding records reported in the past 40 years reflected a range expansion in North America. A range expansion is also unlikely in Minnesota; new records probably reflect increased coverage in the state by dedicated bird and nature enthusiasts. The species is small, secretive, and occurs in remote forests. Like all owls, it vocalizes at night in remote places in the north woods, where few people know its territorial song and fewer yet listen for owls on cold nights in March and April.

Johnson (1982), in his review of raptors in Minnesota, felt that further observations may reveal the Boreal Owl to be a regular nester in the northern regions of Minnesota. In Wisconsin, Robbins (1991) asked a question, “What does one make of this August 1872 record [referring to the bird collected in Fort Atkinson, Wisconsin] and the specimen picked up on the Lincoln-Marathon county line on 11 August 1978 by Follen?” He reasoned that the latter followed the major irruption in 1977–78, similar to Minnesota’s first nesting record. He also remarked that “more listeners . . . afield in northern Wisconsin during late March and April may discover that this species is not as rare as the records might indicate.” However, the Boreal Owl was not reported in the breeding season during the Michigan or Wisconsin breeding bird atlases (Chartier et al. 2013; Cutright et al. 2006).

*Note that the definition of confirmed nesting of a species is different for Breeding Bird Atlas projects, including the definition used by the Minnesota Breeding Bird Atlas, compared with a more restrictive definition used by the Minnesota Ornithologists’ Union. For details see the Data Methods Section.

Figure 1.

Breeding distribution of the Boreal Owl in Minnesota based on the Breeding Bird Atlas (2009 – 2013).

Print Map
Breeding statusBlocks (%)Priority Blocks (%)
Confirmed1 (0.0%)0 (0.0%)
Probable1 (0.0%)0 (0.0%)
Possible2 (0.0%)0 (0.0%)
Observed0 (0.0%)0 (0.0%)
Total4 (0.1%)0 (0.0%)
Table 1.

Summary statistics for the Boreal Owl observations by breeding status category for all blocks and priority blocks (each 5 km x 5 km) surveyed during the Minnesota Breeding Bird Atlas (2009-2013).

Breeding Habitat

The Boreal Owl is a secondary-cavity nesting species that uses holes excavated primarily by woodpeckers, most notably Northern Flickers and Pileated Woodpeckers (Johnsgard 1988). Breeding habitat is broadly described as boreal forest characterized by black and white spruce, aspen, birch, and balsam fir (Hayward and Hayward 1993).

Lane et al. (2001) found territorial Boreal Owls in northeastern Minnesota used poletimber- and sawtimber-sized trees in upland-mixed forest stands; the latter was used more than expected given availability, but open brush/regenerating stands were used less than expected. They summarized that older, upland-mixed forest types were important because they provided suitable nest sites, while lowland conifer habitats were important for foraging and roosting. Tracking radio-equipped male Boreal Owls, Lane (1997) found that the species primarily roosted in lowland black spruce forests even though the habitat type was rare (8.3%) in the study area.

Belmonte (2005) characterized the habitat surrounding 42 known Boreal Owl singing locations in Lake and northern St. Louis Counties of Minnesota. Song perches were primarily in coniferous trees with high basal area and in areas with a high percentage of coniferous canopy cover and a taller canopy compared with random locations.  Examining the habitat near 31 Boreal Owl cavity trees, Belmonte found that upland mixed forests were more common within a 100-m radius of cavity trees, upland conifer stands more common at a 500-m radius, and lowland conifer stands more common at a 1,000-m radius compared with random sites at each of those scales. Considering a landscape perspective, Lane et al. (2001) emphasized that the proximity and juxtaposition of habitat types need to be considered in management and conservation of Boreal Owls. Figure 2 shows a typical habitat configuration for the Boreal Owl in northern Minnesota.

Figure 2.

Typical breeding habitat of the Boreal Owl in Minnesota (© Gerald J. Niemi).

Population Abundance

Partners in Flight estimated a global population of 1.7 million individuals, which includes its Holarctic distribution across the Northern Hemisphere, but Partners in Flight did not provide an estimate for North America, the United States, or Canada (Rosenberg et al. 2016). Environment Canada (2011) reported a large increase in the population since the 1970s based on Christmas Bird Counts but assigned a low reliability to the estimate. They estimated the Canadian population was between 50,000 to 500,000 adults.

Obtaining information on breeding bird trends for the Boreal Owl is difficult because of its low populations. The federal Breeding Bird Survey recorded too few individuals and did not report any results for the species (Sauer et al. 2017).

Lane et al. (2001) censused Boreal Owls along 5 routes in northeastern Minnesota from 1987 to 1992 and found Boreal Owl encounter rates varied from 0.029 detections per km in 1991 to 0.072 detections per km in 1989. There were no statistical differences between years. The Hawk Ridge Bird Observatory in Duluth, Minnesota, coordinated a statewide owl survey from 2005 to 2014 (Grosshuesch and Brady 2015). During the 10-year period of the surveys, only 8 Boreal Owls were recorded, and therefore no detection of statistically valid trends was possible (Grosshuesch and Brady 2015).

In 2015, a targeted effort focused on surveys of suitable habitat and areas where the species had previously been recorded in northern Minnesota (Grosshuesch 2015). A total of 237 points were surveyed on 20 routes in northern Minnesota, some of which were random routes and the rest targeted routes for Boreal Owls. A total of 10 Boreal Owl vocalizations were detected, and all were on targeted routes. These included 7 in Lake County, 1 in St. Louis County, and 1 each in Lake of the Woods and Roseau Counties. These contemporary data illustrate the rarity and very low populations in the northern counties of Minnesota as well as the difficulty of detecting a trend without a substantial effort.

Population density data in Minnesota are rare. Based on routes completed from 1987 to 1992, Lane et al. (2001) estimated an annual average among routes that ranged from 0.014 owls per km2 in 1987 to 0.051 owls per km2 in 1989.

Conservation

Partners in Flight (2017) assigned the Boreal Owl a relatively high Continental Concern Score of 10/20. This score was largely elevated because of multiple concerns, including its low overall population size, threats to its breeding and nonbreeding habitats, and the lack of information on its population trend. The Boreal Owl is designated as a Species in Greatest Conservation Need by the Minnesota Department of Natural Resources (2015). The basis for the designation includes its rarity, declining habitat, its need for a large home range with multiple habitats, and its restricted distribution in the state. The Superior National Forest identified the Boreal Owl as a Regional Forester Sensitive Species. Environment Canada (2011) considers the Boreal Owl to be secure in Canada.

Hayward and Hayward (1993) suggest that disturbance, shooting, trapping, and pesticides do not have major impacts. They add that changes to forest conditions, such as those from logging, are likely to have the greatest effects on the species. To alleviate these impacts, they recommend maintaining large-diameter snags in clear-cuts and employing logging practices that minimize impacts on the Boreal Owl’s primary prey populations, such as red-backed voles. Forestry practices that leave slash distributed across the logged site can help maintain small mammal populations and aid in their recolonization. In Minnesota, harvesting guidelines specify retaining 6 to 12 trees per acre and leaving slash distributed at the site.

Among the greatest threats to the Boreal Owl is climate change. Langham et al. (2015) and the National Audubon Society (2015) designated the species as “climate endangered.” They suggest that any species with the word boreal in its name is susceptible because the boreal forest is one of the biomes believed to be at greatest risk from climate change. They estimated a 51% loss of the species’ winter range by 2080 and said that none of its winter range is stable.

Nest boxes have been effectively used to enhance nesting activity in Fennoscandia (Korpimäki and Hakkarainen 2012) and in the Rocky Mountains (Hayward and Hayward 1993). Management costs for construction, placement, and routine monitoring can prohibit their establishment and long-term effectiveness.

Korpimäki and Hakkarainen (2012) reported that an average of 11,598 nest boxes were maintained in Finland from 1977 to 2009, producing an average of 624 nests per year. This effort has provided them with an impressive database and understanding of the ecology, behavior, and conservation of Boreal Owls in Finland. They have found compelling evidence that the decreasing area of old-growth forest has been the primary reason for the decline of Finland’s Boreal Owl population. In addition, climate change has produced mild and wet winters, which has faded the vole cycle and decreased vole densities in the spring, both of which are extremely important to the survival of Boreal Owls and their young.

The future of the Boreal Owl in Minnesota is unclear and is dubious in North America as well. Unfortunately, its population is so sparse and difficult to detect that it may take years before anyone realizes it may be gone.

  • Belmonte, Lisa Rose. 2005. “Home Range and Habitat Characteristics of Boreal Owls in Northeastern Minnesota.” MS thesis, University of Minnesota.

  • Chartier, Allen T., Jennifer J. Baldy, and John M. Brenneman, eds. 2013. Michigan Breeding Bird Atlas II. Kalamazoo, MI: Kalamazoo Nature Center.

  • Cutright, Noel, Bettie R. Harriman, and Robert W. Howe, eds. 2006. Atlas of the Breeding Birds of Wisconsin. Waukesha: Wisconsin Society of Ornithology, Inc.

  • Eckert, Kim R. 1979. “Another Boreal Owl Nest Found in Cook County.” Loon 51: 198–199.

  • Eckert, Kim R., and Terry L. Savaloja. 1979. “First Documented Nesting of the Boreal Owl South of Canada.” American Birds 33: 135–137.

  • Environment Canada. 2011. Status of Birds in Canada. http://www.ec.gc.ca/soc-sbc/info-info-eng.aspx?sY=2011&sL=e&sB=ATTW&sM=p1&pid=13&sDoc=36&RS=3

  • Green, Janet C., and Robert B. Janssen. 1975. Minnesota Birds: Where, When and How Many. Minneapolis: University of Minnesota Press.

  • Grosshuesch, David A. 2015. Western Great Lakes Region Rare Owl Survey, 2015. Report to U.S. Department of Agriculture Forest Service-Superior National Forest and Minnesota Department of Natural Resources – Nongame Region 2.

  • Grosshuesch, David A., and Ryan S. Brady. 2015. Western Great Lakes Region Owl Survey, 2014 Report. Hawk Ridge Bird Observatory and Wisconsin Bird Conservation Initiative. http://www.hawkridge.org/wp-content/uploads/2015/02/2014-WGL-Spring-Owl-Report_Final.pdf

  • Hatch, Philo L. 1892. First Report: Accompanied with Notes on the Birds of Minnesota. The Geological and Natural History Survey of Minnesota Zoological Series. Minneapolis: Harrison & Smith Printers.

  • Hayward, Gregory D., and Patricia H. Hayward. 1993. “Boreal Owl (Aegolius funereus).” The Birds of North America, edited by Paul G. Rodewald. Ithaca: Cornell Lab of Ornithology. Retrieved from the Birds of North America: https://birdsna.org/Species-Account/bna/species/borowl doi: 10.2173/bna.63

  • Hertzel, Anthony X., and Robert B. Janssen. 1998. County Nesting Records of Minnesota Birds. Minnesota Ornithologists’ Union Occasional Papers, no 2. Minneapolis: The Minnesota Ornithologists’ Union.

  • Johnsgard, Paul A. 1988. North American Owls: Biology and Natural History. Washington, DC: Smithsonian Institute Press.

  • Johnson, David H. 1982. “Raptors of Minnesota – Nesting Distribution and Population Status.” Loon 54: 73–104.

  • Korpimäki, Erkki, and Harri Hakkarainen. 2012. The Boreal Owl: Ecology, Behaviour and Conservation of a Forest-Dwelling Predator. Cambridge: Cambridge University Press.

  • Kumlien, Ludwig, and Ned Hollister. 1903. The Birds of Wisconsin. Bulletin of Wisconsin Natural History Society. Revised by Arlie William Schorger. 1951. Madison: Wisconsin Society for Ornithology, Inc.

  • Lane, William H. 1997. “Distribution and Ecology of Boreal Owls in Northeast Minnesota.” MS thesis, University of Minnesota.

  • Lane, William H., David E. Andersen, and Thomas H. Nicholls. 2001. “Distribution, Abundance, and Habitat Use of Singing Male Boreal Owls in Northeast Minnesota.” Journal of Raptor Research 35: 130–140.

  • Langham, Gary M., Justin G. Schuetz, Trisha Distler, Candan U. Soykan, and Chad Wilsey. 2015. “Conservation Status of North American Birds in the Face of Future Climate Change.” PLoS One 10: e0135350. doi: 10.1371/journal.pone.0135350

  • Matthiae, Thomas M. 1982. “A Nesting Boreal Owl in Minnesota.” Loon 54: 212–214.

  • Minnesota Department of Natural Resources. 2015. Minnesota’s Wildlife Action Plan 2015–2025. St. Paul: Minnesota Department of Natural Resources, Division of Ecological and Water Resources. http://www.dnr.state.mn.us/mnwap/index.html

  • Minnesota Department of Natural Resources. 2017. “Boreal Owl (Aegolius funereus).” Minnesota Biological Survey: Breeding Bird Locations. http://files.dnr.state.mn.us/eco/mcbs/birdmaps/boreal_owl_map.pdf

  • National Audubon Society. 2015. Audubon’s Birds and Climate Change Report: A Primer for Practitioners. Version 1.3. New York: National Audubon Society.

  • Partners in Flight. 2017. Avian Conservation Assessment Database [Online].  http://pif.birdconservancy.org

  • Robbins, Samuel D., Jr. 1991. Wisconsin Birdlife: Population and Distribution Past and Present. Madison: University of Wisconsin Press.

  • Roberts, Thomas S. 1932. The Birds of Minnesota. 2 vols. Minneapolis: University of Minnesota Press.

  • Rosenberg, Kenneth V., Judith A. Kennedy, Randy Dettmers, Robert P. Ford, Debra Reynolds, John D. Alexander, Carol J. Beardmore, Peter J. Blancher, Roxanne E. Bogart, Gregory S. Butcher, Alaine F. Camfield, Andrew Couturier, Dean W. Demarest, Wendy E. Easton, Jim J. Giocomo, Rebecca Hylton Keller, Anne E. Mini, Arvind O. Panjabi, David N. Pashley, Terrell D. Rich, Janet M. Ruth, Henning Stabins, Jessica Stanton, and Tom Will. 2016. Partners in Flight Landbird Conservation Plan: 2016 Revision for Canada and Continental United States. Partners in Flight Science Committee. http://www.partnersinflight.org/wp-content/uploads/2016/08/pif-continental-plan-final-spread-single.pdf

  • Sauer, John R., Daniel K. Niven, James E. Hines, David J. Ziolkowski Jr., Keith L. Pardieck, Jane E. Fallon, and William A. Link. 2017. The North American Breeding Bird Survey, Results and Analysis 1966–2015. Version 12.23.2015. Laurel, MD: U.S. Geological Survey Patuxent Wildlife Research Center. https://www.mbr-pwrc.usgs.gov/bbs/

  • Schorger, Arlie W. 1926. “Richardson’s Owl (Cryptoglaux funereal richardsoni) in Cook County, Minnesota.” Auk 43: 544.