Data Zone
Justification of Red List category
This species has a moderately small population which continues to decline in the northern and western parts of its range; as a result it is considered Near Threatened. Further evidence that confirms declines are more widespread and severe than currently thought may result in this species being uplisted to a higher threat level.
Population justification
Its population size was estimated at c.15,000 mature individuals (Rich et al. 2004). However, this has likely declined in recent years and population surveys are urgently required to accurately quantify the population size of this species.
Trend justification
There has been no direct estimation of the overall population trend for this species but it is suspected to have undergone considerable declines. Subspecies caurina is estimated to be in significant decline, at 3.8% per year range-wide and 8.4% per year in Washington State (1985-2013; 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). Whilst declines are rapid in a number of locations however, the species appears stable in some areas, such as Arizona (B. Bird in litt. 2011) and for subspecies huachucae, Mexico, where forestry activities typically modify rather than destroy habitat (Lammertink et al. 1996, J. M. Lammertink in litt. 1998); subspecies huachucae may actually be exhibiting localised increases in some subpopulations throughout New Mexico (Ganey et al. 2014b). Despite this however, the overall population is still suspected to be in considerable 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, a conclusion supported by Partners in Flight (2019) (7-26.9% across three generations), and as such is placed in the range 20-29% over 3 generations (c.21.3 years).
Strix occidentalis has five subspecies: caurina ('Northern Spotted Owl') is estimated to number 3,778 pairs and 1,001 territorial individuals from south-west British Columbia, Canada, to north California, USA, although this number may have declined in recent years; 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 1988, 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 (1985-2013; 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, Gutiérrez et al. 2017).
Most populations strongly associate with either old-growth conifer or pine-oak forests (Johnsgard 1988, Gutiérrez et al. 1995), but some lucida also occur in heavily logged secondary pine-oak forest, warmer and drier conditions and on bare rocky cliffs and canyons (Lammertink et al. 1996, J. M. Lammertink in litt. 1998, U. S. Fish and Wildlife Service 2012, Bowden et al. 2015). 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) on cliff-ledges in steep-walled canyons (and occasionally in caves (Wilk et al. 2018). Eggs are laid from March to May. Young birds are obligate dispersers, whilst unpaired birds or those that have failed to breed previously also disperse (Forsman et al. 2002, Blakesley et al. 2006, Ganey et al. 2014a); 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.
The two principle threats to the Spotted Owl are currently considered to be competition with the Barred Owl (Strix varia) and logging of the species's habitat. Spotted Owl faces strong competition from Barred Owl which is gradually displacing Spotted Owls from much of the northern part of their range, outcompeting Spotted Owls for food and space, reducing Spotted Owl occupancy and breeding propensity, and occasionally hybridising (Kelly and Forsman 2004, Gutiérrez et al. 2007, Wiens et al. 2014, Dugger et al. 2016, Long and Wolfe 2019, Mangan et al. 2019). 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, Gutiérrez et al. 2017, Wood et al. 2019). Degradation and fragmentation of its habitat through clear felling and selective logging of large trees is a primary threat to the species (Gutiérrez et al. 1995, Jones et al. 2018); with habitat fragmentation shown to correlate with decreased probability of survival (Schilling et al. 2013); the rate of logging is however reported to have declined notably in the past 20-30 years (Gutiérrez et al. 2017, J. Dunk in litt. 2020). This has been compounded by the removal of a legal requirement that the U. S. Forest Service assess the viability of wildlife on national forest lands (Noon and Blakesley 2006). Forest loss throughout the species's range is currently estimated at ~7.25% over three generations (Tracewski et al. 2016). 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 high-severity fire (Jones et al. 2019) and drought associated with climate change (see Peery et al. 2011, Jones et al. 2016, T. Supplee in litt. 2011, Gutiérrez et al. 2017, Wan et al. 2019) although low- and moderate-severity fires are not thought to significantly affect the species (see Bond et al. 2002, Roberts et al. 2011, Lee et al. 2012, Willey and van Riper III 2014, Ganey et al. 2017) and may even create favourable foraging conditions (Eyes et al. 2017). 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). 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). Enhanced exposure to anticoagulant rodenticides (AR), illegally utilised, in and widely contaminating the remote forests of California, USA, may also be adversely impacting the species (Gabriel et al. 2018, Wiens et al. 2019a). 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, Gutiérrez et al. 2017).
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 created 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 (Verner et al. 1992, 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, Dunk et al. 2019). 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 is underway (Oregon Fish and Wildlife Service and U. S. Fish and Wildlife Service 2013, A. Franklin in litt. 2016, Wiens et al. 2019b).
Text account compilers
Everest, J.
Contributors
Benstead, P., Bird, B., Bird, J., Butcher, G., Dunk, J., Franklin, A., Gutiérrez, R., Haig, S., Heiken, D., Holmer, S., Isherwood, I., Lammertink, M., Supplee, T., Taylor, J., Wege, D. & Westrip, J.R.S.
Recommended citation
BirdLife International (2024) Species factsheet: Spotted Owl Strix occidentalis. Downloaded from
https://datazone.birdlife.org/species/factsheet/spotted-owl-strix-occidentalis on 23/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 23/12/2024.