Boreal Owl (Aegolius funereus)
Associated Species: Other species that may use habitat in a similar way and/or respond similarly
to threats, management, and conservation activities include Hammond's Flycatcher, Golden-crowned Kinglet, and Ruby-crowned Kinglet.
Distribution: The continental distribution of Boreal Owls follows the distribution of the boreal
forest--from central Alaska south and east in a broad band across Canada, into the northern
regions of the Great Lakes states and the Northeast, and down through the Northern Rockies
south into northwestern Wyoming. The population in the Southern Rockies may be disjunct,
although more intensive studies may show connections between this population and that of the
Northern Rockies. The birds are widespread in the spruce-fir habitat type in Physiographic Area
Habitat Requirements: Boreal Owls primarily reside in mature and old-growth coniferous
forests, especially spruce-fir (and occasionally lodgepole pine) in Physiographic Area 62.
Structural characteristics of occupied territories vs. unoccupied sites include greater basal area,
more large trees, and less understory vegetation. Multiple canopy layers are typical. The high
canopy closure limits the development of low vegetation in summer and crusted snow in winter,
allowing the owls year-round access to prey. The high-elevation distribution of spruce-fir forests
also conveys a thermal advantage, as the owls apparently do not tolerate high temperatures. The
nests are in natural or flicker-excavated cavities in large trees or snags; nest trees in an Idaho
study averaged 64 cm (25 in) dbh (Hayward et al. 1993).
Ecology: Boreal Owls do not migrate, but they are nomadic in response to cyclic prey
populations. Nesting is initiated as early as mid April and most young leave the nest by mid June.
The diet consists of small mammals, especially red-backed voles.
Management Issues and Conservation Recommendations: The distribution and abundance of
Boreal Owls is largely tied to nest cavity availability (they require large trees and snags for
nesting) and prey populations. The principal prey species, the red-backed vole, prefers mature,
mesic forests with high canopy closure and large downed woody material; it is absent from
clearcut areas, but local populations appear largely unaffected by patch cuts (<1.2 ha; 3 ac) or
selection cuts (Martell 1983). Utilize uneven-aged management, patch cuts with long rotations
(150 years), and other silvicultural practices that preserve these conditions.
Status and Reasons for Concern: Boreal Owls require large areas of mature spruce-fir
forest--home ranges in Colorado have been measured at about 1500 ha (3,700 ac) (Palmer
1986). By protecting habitat for Boreal Owls, managers will ensure habitat protection for other
spruce-fir species. Boreal Owls are classified as a Sensitive Species in U.S. Forest Service Region
2. Due to this species' nocturnal habits and early nesting season, no data from BBS or other
long-term monitoring projects are available. Grande Mesa and Uncompahgre National Forests
began an attempt to monitor this species with a nest box program in 1993. This species is
monitored by MCB with nocturnal surveys.
Biological Objective: Maintain the current distribution of the Boreal Owl as determined by
nocturnal surveys of the MCB monitoring program, the nest box project of Grande Mesa and
Uncompahgre National Forests, and other monitoring programs.
Selected References: Andrews and Righter 1992, Hayward 1997, Hayward and Hayward 1993,
Hayward and Verner 1994, Kingery 1998.