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BC Conservation Data Centre: Species Summary


Strix occidentalis
Spotted Owl


 
Scientific Name: Strix occidentalis (Xántus de Vesey, 1860)
Scientific Name Synonyms: Strix occidentalis caurina
English Name: Spotted Owl
English Name Synonyms: Northern Spotted Owl
 
Classification / Taxonomy
Scientific Name - Concept Reference: American Ornithologists' Union (AOU). 1998. Check-list of North American birds. Seventh edition. American Ornithologists' Union, Washington, D.C. [as modified by subsequent supplements and corrections published in The Auk]. Also available online: http://www.aou.org/.
Classification Level: Species
Taxonomy Comments: The CDC reports on this element at the species level, as only one subspecies occurs within the province (Strix occidentalis caurina).
Species Group: Vertebrate Animal
Species Code: B-SPOW
Kingdom Phylum Class Order Family
Animalia Craniata Aves Strigiformes Strigidae
   
Conservation Status / Legal Designation
Global Status: G3G4 (Apr 2016)
Provincial Status: S1 (Apr 2018)
BC List: Red
Provincial FRPA list: Y (May 2004)  
Provincial Wildlife Act:
COSEWIC Status: Endangered (Mar 2008)
COSEWIC Comments: Caurina Subspecies
SARA Schedule: 1  -  Endangered (Jun 2003)
General Status Canada: 1 - At Risk (2005)
Migratory Bird Convention Act:
   
Ecology & Life History
General Description: A large, dark-eyed, round-headed, brown owl with whitish spotting on the head, back, and underparts (spotted breast, barred belly).
Identification Comments: The Northern Spotted Owl is a medium sized owl with chocolate brown body feathers, and a regular pattern of elliptical creamy white spots. It has a large round facial disk with dark brown eyes and lacks ear tufts. Females are slightly larger in size (Farrand 1983) and have higher pitched calls than those of males (Forsman et al. 1984)
Global Reproduction Comments: Egg dates: mainly late March or early to mid-April in California, April in Arizona and New Mexico, early April in Oregon. Clutch size is 2-4, usually 2. Incubation, by female (fed by male), lasts about 30 days. Young leave nest at about 5 weeks, fly at about 6 weeks, stay near nest for several weeks, fed by adults until late summer, independent by early fall. First breeds at 2-3 years; may not breed every year; life-long pair bond.
Provincial Reproduction Comments: Northern Spotted Owls have the smallest clutch of all North American owls with an average of only two per clutch, may occasionally have three (Gutierrez et al. 1995). Typically only one brood. The incubation period is estimated to be approximately 30 days (Forsman et al. 1984). All incubation is done by the female while males provides food for both females and juveniles (Forsman et al. 1984). For the first 8-10 days the female broods the nestlings continuously. Within 34-36 days of hatching the young are ready to leave the nest. Individuals have been recorded to breed in their first year (Miller et al. 1985), however, most pairs are 2-3 years old before breeding and do not breed every year (Franklin et al. 1999; Forsman et al. 2002). Spotted Owls are known to sometimes not breed over periods of 5-6 years (Gutierrez et al. 1995).
Global Ecology Comments: Occurs at low densities (one pair per several sq km). Annual home range for a pair may be several thousand acres. Juveniles disperse usually less than 100 km but sometimes up to more than 150 km, often more than 25 km. See files for subspecies.
Provincial Ecology Comments: Population density of Northern Spotted Owl in B.C. is uncertain. Annual territory home range is estimated to be 3200 ha (SOMIT 1997a; Blackburn . 2002), whereas breeding territory size is estimated to be 1600 ha (Keystone 2004). Home range is thought to overlap between paired individuals (Forsman et al. 1984). Individuals of typically monogamous pairs are solitary over winter and begin roosting together near the nest 4-6 weeks prior to egg laying. Major predators of Northern Spotted Owls are Great Horned Owl (Bubo virginianus) and Northern Goshawk (Accipiter gentilis) (Gutierrez et al. 1985). The Great Horned Owl and Barred Owl (Strix varia) compete for similar food as Spotted Owl in overlapping areas. Barred Owl is known to significantly displace Spotted Owl (Hamer 1988, Kelly et al. 2003). Northern Spotted Owl is generally long-lived (Gutierrez et al. 1995).
Migration Characteristics:
(Global / Provincial)
 
    Nonmigrant:
    Local Migrant:
    Distant Migrant:
    Within Borders Migrant:
Y / Y
Y / N
N / N
na / N
Global Migration Comments: Individuals may make seasonal elevational migrations; see files for subspecies.

These owls tend to concentrate their foraging activities near the nest, particularly during the breeding season (Solis and Gutierrez 1990).
Provincial Mobility & Migration Comments: Non-migratory. Juveniles are obligate dispersers and typically leave their natal area in late September (Gutierrez et al. 1985; Miller 1989; MWLAP 2003). Female juveniles typically disperse farther than males, with 50% of female and male juveniles settling within 22.9-24.5 km and 13.5-14.6 km from their natal areas, respectively (Forsman et al. 2002).
Habitats:
(Type / Subtype / Dependence)
Forest / Conifer Forest - Dry / Unknown
Forest / Conifer Forest - Mesic (average) / Unknown
Forest / Conifer Forest - Moist/wet / Unknown
Riparian / Riparian Forest / Unknown
Global Habitat Comments: Dense forest and deep wooded canyons; generally in mature stands or old growth (e.g., Bias and Gutiérrez. 1992); requires cool summer roosts. Nests on broken tree top, cliff ledge, in natural tree cavity, or in tree on stick platform, often the abandoned nest of hawk or mammal; sometimes in cave. See files for subspecies.
Provincial Habitat Comments: The Northern Spotted Owl preferentially selects old coniferous forests for foraging, roosting and nesting (Forsman et al. 1984; Carey et al. 1992), with large overstorey trees (>75 cm dbh), multilayered canopy, large decaying fallen trees and large diameter standing dead trees; these stands are typically dominated by trees >200 years (Thomas et al. 1990). Habitat selection is likely influenced by prey availability and abundance, availability of suitable nest and roosts sites, and adequate cover from predators (Carey et al. 1992, Forsman and Giese 1997). Spotted Owls do not create their nest structures, but often use tree cavities, deformities of large trees (e.g., depressions in the top of broken-topped trees, or platforms constructed by other birds or by natural accumulations of debris) (Forsman et al. 1984; Buchanan et al. 1993; Forsman and Giese 1997). Nest sites are located below the overhead canopy, thereby providing overhead cover and seclusion to the nest.
Food Habits: Carnivore: Adult, Immature
Global Food Habits Comments: Small mammals predominate in diet; also eats various birds and sometimes large insects. Sometimes stores food for future use. See files for subspecies.
Provincial Food Habits Comments: Spotted Owls generally prey on nocturnal or aboreal forest mammals (Thomas et al. 1990), although they have been known to predate on a broad array of taxa including birds, amphibians and insects (Forsman et al. 1984). The composition of their diet varies among regions and by forest type. In B.C., the largest contribution (41.2%) to the owl's diet is Northern Flying Squirrels (Glaucomys sabrinus), and Bushy-tailed Woodrats (Neotoma cinerea) (27.8%) (Horoupian et al. 2000). Flying squirrels appear almost twice as abundant in old-growth as any other forest types (Carey 1995; Ransome 2001). The Spotted owl is a sit and wait predator and flies using a gliding flight motion.
Global Phenology: Crepuscular: Adult, Immature
Nocturnal: Adult, Immature
Global Phenology Comments: Roosts during the day; hunts at dusk and at night. May leave roost during day to capture prey near roost (e.g., see Sovern et al. 1994), retrieve cached prey, or to drink or bathe in stream.
Provincial Phenology:
(1st half of month/
2nd half of month)
Jan: Present / Present
Feb: Present / Present
Mar: Active / Reproducing
Apr: Eggs present outside adult / Eggs present outside adult
May: Eggs present outside adult / Active
June: Active / Active
July: Active / Active
Aug: Active / Active
Sept: Active / Active
Oct: Present / Present
Nov: Present / Present
Dec: Present / Present
Provincial Phenology Comments: Crepuscular. Nocturnal. Roosts during the day; hunts at dusk and at night. May leave roost during day to capture prey near roost (Sovern et al. 1994), retrieve cached prey, or to drink or bathe in streams or standing water.
Colonial Breeder: N
Length(cm)/width(cm)/Weight(g): 45/ / 637
Elevation (m) (min / max): Global: 
Provincial:  0 / 1370
   
 
Distribution
Endemic: N
Global Range Comment: RESIDENT: southwestern British Columbia (Dunbar et al. 1991) south through western Washington and western Oregon to southern California and northern Baja California (probably); in Rocky Mountain region from southern Utah and central Colorado south through the mountains of Arizona, New Mexico, extreme western Texas (Guadalupe Mountains), northern Sonora, Chihuahua, and Nuevo Leon to Jalisco, Michoacan, and Guanajato (AOU 1983).
 
Authors / Contributors
Global Information Author: HAMMERSON, G.
Last Updated: Mar 28, 1995
Provincial Information Author: Manning, T.
Last Updated: Jan 27, 2005
   
References and Related Literature
American Ornithologists' Union (AOU). 1983. Check-list of North American Birds, 6th edition. Allen Press, Inc., Lawrence, Kansas. 877 pp.
Barrowclough, G. F., and R. J. Gutierrez. 1990. Genetic variation and differentiation in the spotted owl (STRIX OCCIDENTALIS). Auk 107:737-744.
Barrows, C.W. 1981. Roost selection by spotted owls: an adaptation to heat stress. Condor 83:302-309.
Blackburn, I., and S. Godwin. 2004. Status of the Northern Spotted Owl (Strix occidentalis caurina) in British Columbia. B.C. Minist. Water, Land and Air Protection, Biodiversity Branch, Victoria BC. Wildl. Bull. No. B-118.
Blackburn, I.R., et al. 2000. Spotted Owl Management Plan for the Chilliwack and Squamish Forest District. P. 289 in L.M. Darling, ed. 2000. Proc. Conf. on the Biology and Manage. Species and Habitats at Risk, Kamloops, B.C., 15-19 Feb., 1999. Vol. 1; B.C. Minist. Environ., Lands and Parks, Victoria, BC, and Univ. College of the Cariboo, Kamloops, BC. 490pp.
Blood, D.A. 1998. Northern Spotted Owl. B.C. Minist. Environ., Lands and Parks, Wildl. Branch. 6pp.
Bosakowski, T. 1987. Census of barred owls and spotted owls. Pages 307-308 in Nero, R. W., et al., eds. Biology and conservation of northern forest owls. USDA For. Serv., Gen. Tech. Rep. RM-142.
Boyce, M. S., and L. L. Irwin. 1990. Viable populations of spotted owls for management of old growth forests in the Pacific Northwest. Pages 133-135 in Mitchell et al., eds. Ecosystem management: rare species and significant habitats. New York State Mus. Bull. 471.
British Columbia Ministry of Water, Land and Air Protection. 2004u. Spotted Owl in Accounts and measures for managing identified wildlife. British Columbia Ministry of Water, Land and Air Protection, Victoria, BC. 52pp.
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Campbell, R. W., E. D. Forsman, and B. M. Van Der Ray. 1984. Land management report No. 242. British Columbia Ministry of Forests, Victoria. 115 pp.
Campbell, R.W., N.K. Dawe, I. McTaggart-Cowan, J.M. Cooper, G.W. Kaiser, and M.C.E. McNall. 1990b. The Birds of British Columbia Vol. 2: Nonpasserines: Diurnal Birds of Prey through Woodpeckers. Royal British Columbia Museum, Victoria, BC.
Carey, A. B., J. A. Reid, and S. P. Horton. 1990. Spotted owl home range and habitat use in southern Oregon Coast Ranges. J. Wildlife Management 54:11-17.
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Clark, R. J., D. G. Smith, and L. H. Kelso. 1978. Working bibliography of owls of the world. National Wildlife Federation, Sci. & Tech. Ser. No. 1. 336 pp.
COSEWIC. 2000d. COSEWIC assessment and update status report on the Northern Spotted Owl Strix occidentalis caurina in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + 14 pp.
COSEWIC. 2008o. COSEWIC assessment and update status report on the Spotted Owl Strix occidentalis caurina Caurina subspecies, in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + 48 pp.
Courtney, S.P. et al. 2004. Scientific evaluation of the status of the Northern Spotted Owl. Sustainable Ecosystems Institute. Portland, OR. 508pp.

Craig, G. A. 1986. The spotted owl and wise forest use. Western Timber Association, Sacramento, CA. 69 pp.
Dawson, W. R., J. D. Ligon, and J. R. Murphy. 1987. Report of the Scientific Advisory Panel on the Spotted Owl. Condor 89:205-229.
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Eckert, Allan W. 1978. The Owls of North America. Weather-vane Books, New York. 278 pp.
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Please visit the website Conservation Status Ranks for definitions of the data fields used in this summary report.

Suggested Citation:

B.C. Conservation Data Centre. 1995. Species Summary: Strix occidentalis. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed May 23, 2024).