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Strix occidentalis

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA AVES STRIGIFORMES STRIGIDAE

Scientific Name: Strix occidentalis
Species Authority: (Xantus De Vesey, 1860)
Common Name(s):
English Spotted Owl
Spanish Búho Manchado, Cárabo Californiano

Assessment Information [top]

Red List Category & Criteria: Near Threatened ver 3.1
Year Published: 2013
Date Assessed: 2013-11-01
Assessor(s): BirdLife International
Reviewer(s): Butchart, S.
Contributor(s): Bird, B., Butcher, G., Haig, S., Heiken, D., Holmer, S., Lammertink, M. & Supplee, T.
Facilitator/Compiler(s): Benstead, P., Bird, J., Isherwood, I., Taylor, J., Wege, D.
Justification:
This species has a moderately small population which continues to decline in northern and western parts of its range; as a result it is considered Near Threatened.

History:
2012 Near Threatened

Geographic Range [top]

Range Description: Strix occidentalis has a population of c.15,000 individuals in four subspecies: caurina has a minimum of 3,778 pairs and 1,001 territorial individuals from south-west British Columbia, Canada, to north California, USA; the nominate has a minimum of 3,050 individuals in central and south California, USA, and (formerly) Baja California, Mexico; lucida has a minimum of 777-1,554 individuals from Utah and Colorado to Arizona, New Mexico and extreme west Texas, USA, and also occurs in Sonora, Chihuahua and Nuevo León to Jalisco, Durango, Michoacán and Guanajuanto, Mexico (Johnsgard 1988a, Sibley and Monroe 1990, Gutiérrez et al 1995, Lammertink et al. 1996, AOU 1998); and juanaphillipsae has been recently described from the State of México (Dickerman 1997). Mexican populations may be stable because forestry activities there typically modify rather than destroy habitat (Lammertink et al. 1996, J. M. Lammertink in litt. 1998). Most other populations are declining and, in some, the decline is accelerating because of clear-felling and selective logging (Gutiérrez et al 1995, Noon and McKelvey 1996). Subspecies caurina is estimated to be in significant decline, at 3% per year range-wide and 7% per year in Washington State (S. Holmer in litt. 2011), and is close to extinction in Canada. The most recent information on the numbers of subspecies lucida in Arizona indicates that the population there is stable, but the population in New Mexico is estimated to be declining at a rate of 6% per year (B. Bird in litt. 2011). Overall, the population is suspected to be in decline, although the rate of decline has not been estimated.

Countries:
Native:
Canada; Mexico; United States
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Its population size is estimated at c.15,000 mature individuals (Rich et al. 2004).

Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Most populations strongly associate with old-growth conifer or oak forests (Johnsgard 1988a, Gutiérrez et al 1995), but lucida also occurs in heavily logged secondary pine-oak forest, warmer and drier conditions and even bare rocky canyons (Lammertink et al. 1996, J. M. Lammertink in litt. 1998). While some degree of logging may aid foraging, the species associates with old trees and old-growth forest for nesting and roosting (Dugger et al. 2005). It occurs from sea-level to 1,200 m in the northern part of its range, and to 2,700 m in the southern part. Nests are generally in trees within closed-canopy forest, (usually in cavities or on stick platforms constructed originally by raptors, wood rats or squirrels), in caves, or on cliff-ledges in steep-walled canyons. Eggs are laid from March to May. Young and unpaired birds disperse, which is an adaptation that has been shown to improve territory quality (Blakesley et al. 2006) and helps to sustain some sink populations. It feeds principally on nocturnal mammals.

Systems: Terrestrial

Threats [top]

Major Threat(s): Degradation and fragmentation of its habitat through clear felling and selective logging is the primary threat to the species. This has been compounded by the removal of a requirement that contractors assess the viability of wildlife on U.S. Department of Agriculture Forest Service lands (Noon and Blakesley 2006). Populations in the southwest of its range are threatened by habitat fragmentation caused by fire and drought associated with climate change (T. Supplee in litt. 2011), and habitat loss to wildfire has been greater than expected in recent years, raising the economic value of remaining habitat (D. Heiken in litt. 2012). Projected climate change may result in longer fire seasons and larger more intense fires, as well as increased tree mortality from drought and insects, and uncertainty over the viability of habitat restoration. Further effects from climate change could include changes in the frequency and duration of inclement weather during the breeding season (D. Heiken in litt. 2012). Timber harvesting on private land is a significant threat, as well as renewed pressure to eliminate protections for the species on federal land in Oregon, in order to allow increased logging (T. Supplee in litt. 2011). Unfavourable management includes intensive thinning of suitable habitat, which is expected to result in declines over the short term (T. Supplee in litt. 2011), as well as logging and manipulation of canopy vegetation to reduce the risk of wildfire (B. Bird in litt. 2012, D. Heiken in litt. 2012). It faces strong competition from Barred Owl Strix varia which is gradually displacing Spotted Owls from much of the northern part of their range, outcompeting it for food and space and occasionally hybridising (Kelly and Forsman 2004). The extent to which Barred Owls have been responsible for recent continuing declines in Northern Spotted Owl populations remains uncertain. Potentially serious threats include West Nile virus, which is fatal to the species, the potential loss of habitat to Sudden Oak Death Syndrome (D. Heiken in litt. 2012), and avian malaria, which has been discovered in the species and found to weaken infected individuals, probably reducing reproductive success (Ishak et al. 2008, D. Heiken in litt. 2012).

Conservation Actions [top]

Conservation Actions: Conservation Actions Underway
CITES Appendix II. The northern (caurina) and Mexican (lucida) subspecies are listed as Threatened under the U.S. Endangered Species Act, and are the subject of recovery plans (S. Holmer in litt. 2011, B. Bird in litt. 2012). The Northwest Forest Plan was drawn up to provide protection and reduce rates of timber harvest leading to habitat destruction. Protected Activity Centres are advocated for as an effective mechanism of conserving the species in parts of its range (Willey and van Riper III 2007).  A captive breeding programme was started at the  Mountain View Conservation and Breeding Centre, British Columbia, with a second attempt in Woodland Park Zoo in Seattle.  Neither have so far had much success (Moore, 2013).

Conservation Actions Proposed
Continue to monitor population trends across its range. Large reserves, encompassing suitable habitat and widely distributed are needed to retain the owl's current range. Calls have been made for captive breeding of birds from the tiny remaining British Columbian population. To prevent local extinction a halt to logging operations is required in parts of its range. Conduct research into the extent to which Barred Owls have precipitated recent declines in Spotted Owls, and investigate the threats posed by West Nile virus, avian malaria and climate change. Counter unfavourable management policies designed to reduce wildfire risk.


Citation: BirdLife International 2013. Strix occidentalis. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 01 September 2014.
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