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 3.8% per year range-wide and 8.4% per year in Washington State (Dugger et al. 2016). The New Mexico population of subspecies lucida is estimated to be declining at 6% per year (B. Bird in litt. 2011), while the species may have declined by c.50% between 1990 and 2012 in the Sierra Nevada (Tempel et al. 2014b). 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). There has been no direct estimation of the overall rate of decline, but the species is conservatively assessed as declining at a rate at least approaching the threshold for Vulnerable, and as such is placed in the range 20-29% over 3 generations (c.30 years).
Strix occidentalis has five subspecies: caurina ('Northern Spotted Owl') has a minimum of 3,778 pairs and 1,001 territorial individuals from south-west British Columbia, Canada, to north California, USA; the nominate ('California Spotted Owl') has a minimum of 3,050 individuals in central and south California, USA, and (formerly) Baja California, Mexico; and lucida, juanaphillipsae and huachucae ('Mexican Spotted Owl') (see del Hoyo and Collar 2014). Subspecies huachuacae occurs from Utah and Colorado to Arizona, New Mexico and extreme west Texas, USA, while lucida 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, del Hoyo and Collar 2014), and juanaphillipsae has been recently described from the State of Mexico (Dickerman 1997). Mexican Spotted Owl may be considered to be declining (U. S. Fish and Wildlife Service 2012), although 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) and at least locally in New Mexico some subpopualations may be increasing (Ganey et al. 2014b). 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 3.8% per year range-wide and 8.4% per year in Washington State (Dugger et al. 2016), and is close to extinction in Canada. California Spotted Owl is declining in the Sierra Nevada, apart from at one site in a National Park (see Tempel et al. 2014b, R. Gutiérrez in litt. 2016). Overall, the population is suspected to be in decline.
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, U. S. Fish and Wildlife Service 2012, J. M. Lammertink in litt. 1998). 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 birds disperse, as too may unpaired birds or those that have failed to breed previously (Forsman et al. 2002, Blakesley et al. 2006, Ganey et al. 2014a) and this may help to sustain some sink populations. It may make some movements in winter, including to recently burnt areas as these can have greater food availability (Ganey et al. 2014b). 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; with habitat fragmentation shown to correlate with decreased probability of survival (Schilling et al. 2013). 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, California, and dry inland forests of the Pacific Northwest are threatened by habitat loss and fragmentation caused by fire and drought associated with climate change (see Peery et al. 2011, Jones et al. 2016, T. Supplee in litt. 2011, R. Gutiérrez in litt. 2016), although there has been a suggestion that the species may persist with a degree of habitat burning (see Roberts et al. 2011, Lee et al. 2012, Willey and van Riper III 2014). 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 hotter and drier summers with 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 may affect different areas differently (see Peery et al. 2011) and could include changes in the frequency and duration of inclement weather during the breeding season (D. Heiken in litt. 2012); and in the Pacific northwest it may lead to wetter and warmer winters (Glenn et al. 2010). 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, R. Gutiérrez in litt. 2016). 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). The species may also face high levels of disturbance, especially in recreational areas where it occurs such as National Parks (U.S. Fish and Wildlife Service 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 Spotted Owls for food and space and occasionally hybridising (Kelly and Forsman 2004, Dugger et al. 2016). While S. varia is not known to have affected the population trend in California yet, some hybrids have been noted there and it does appear to be spreading into the range of California Spotted Owl (Tempel et al. 2014a, R. Gutiérrez in litt. 2016). Energy development and associated habitat loss and mortalities from collisions with powerlines could also be affecting this species, but the degree of impact is essentially unknown (U.S. Fish and Wildlife Service 2012). Potentially serious threats include West Nile virus, which is fatal to the species (although it may be absent from some subpopulations [Hull et al. 2010]), 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). Other potential threats have been put forward, for instance it has been mooted that water management could possibly have an impact on the species through indirect effects, though these will require further study (U.S. Fish and Wildlife Service 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 (U. S. Fish and Wildlife Service 2011, 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). In 2012 9.6 million acres of habitat was designated as critical habitat for the Northern Spotted Owl by U. S. Fish and Wildlife Service (Society for Conservation Biology 2012). 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). Experimental removal of Barred Owls has been proposed and is underway (Oregon Fish and Wildlife Service and U. S. Fish and Wildlife Service 2013, A. Franklin in litt. 2016).
Text account compilers
Taylor, J., Westrip, J., Isherwood, I., Wege, D., Benstead, P., Bird, J.
Supplee, T., Franklin, A., Heiken, D., Haig, S., Holmer, S., Gutiérrez, R., Lammertink, M., Bird, B., Butcher, G.
BirdLife International (2018) Species factsheet: Strix occidentalis. Downloaded from http://www.birdlife.org on 23/04/2018. Recommended citation for factsheets for more than one species: BirdLife International (2018) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 23/04/2018.