Justification of Red List Category
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.
Its population size is estimated at c.15,000 mature individuals (Rich et al. 2004).
Trend analyses using Christmas Bird Count (CBC) data gathered since 1965-1966 suggest that this species’s population is not declining, and may even be increasing slightly (Butcher and Niven 2007); however, CBC data are not regarded as sufficiently reliable for monitoring population trends in this species because it is rarely encountered during the CBC and because it is a highly desired species by observers, perhaps resulting in special efforts to find it - efforts that may have become more successful over time with the accumulation of knowledge (G. Butcher in litt. 2011). 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). The New Mexico population of subspecies lucida is estimated to be declining at 6% per year (B. Bird in litt. 2011). Although the species appears to be stable in some areas, such as Arizona (B. Bird in litt. 2011), the overall population is suspected to be in decline owing primarily to on-going habitat disturbance by inappropriate silvicultural management including clear-felling and degradation (del Hoyo et al. 1999); however, the overall rate of decline has not been reliably estimated.
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.
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.
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 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).
Text account compilers
Benstead, P., Bird, J., Isherwood, I., Taylor, J. & Wege, D.
Bird, B., Butcher, G., Haig, S., Heiken, D., Holmer, S., Lammertink, M. & Supplee, T.
BirdLife International (2017) Species factsheet: Strix occidentalis. Downloaded from http://www.birdlife.org on 22/10/2017. Recommended citation for factsheets for more than one species: BirdLife International (2017) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 22/10/2017.