California Spotted Owl (Strix occidentalis occidentalis)

April 17, 2017

On March 17, 2017, the U.S. Fish and Wildlife Service formally requested information from members of the public with scientific information and expertise relative to the California spotted owl (CSO). The Service intends to collect and analyze the best scientific and commercial data available related to the CSO to assist in the development of a CSO Conservation Objectives Report. The report is is expected to be completed in 2017. The report will be peer reviewed, and will be used to inform specific conservation strategies and plans.

In response to the request, Sierra Forest Legacy and coalition partners provided a detailed summary of the science necessary to achieve conservation of the California spotted owl. Read the 42 page letter here.

October 28, 2016

On June 23, 2016, the Forest Service released its current draft of the California Spotted Owl Conservation Strategy. While one would think that the strategy would be based on the science assessment (see below), the draft conservation strategy is so biased towards maintaining logging priorities that it appears to have little to do with either science or conservation. The document and associated appendices can be reviewed at this Forest Service website, and our letter summarizing our key concerns (October 28, 2016) can be downloaded here.

Earlier this summer, the Forest Service research branch in California (PSW) released the California spotted owl assessment, the most current scientific review of the status of the owl. The results are soon to be published in the General Technical Report format, after the draft has been edited, but you can download the long awaited draft report here. The findings in this report should have been translated directly into the conservation strategy, but apparently the lack of leadership in the Forest Service and the confusion of conflicting priorities has once again derailed what should have been a straight forward process.

Citation for the Scientific Assessment: Gutiérrez, R.J.; Manley, Patricia N.; Stine, Peter A., tech. eds. [In press]. The California spotted owl: current state of knowledge. Gen. Tech. Rep. PNW-GTR. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station.

March 15, 2016

Interim Recommendations for Management for the California Spotted Owl

On October 9, 2014, plaintiffs SFL and co-litigants agreed to a settlement agreement with the Forest Service to end the fifteen year long battle over the agency's revisions of forest plans in the national forests of the Sierra Nevada. This resolved SFL's lawsuit filed in 2005 against the Forest Service relative to the 2004 revision of the 2001 Sierra Framework forest plan. New forest plans produced under the new 2012 planning rule will replace the 2004 SIerra Framework amendment, providing a new window for developing effective conservation measures for species at-risk such as the California spotted owl.

The terms of the settlement included an agreement that the agency would produce new conservation strategies for the Pacific fisher and the California spotted owl. The agency also agreed to work with SFL to develop a Memorandum of Understanding (MOU) for the increased use of managed fire for ecological benefit; and to include an analysis in the new forest plans for post-fire, complex early-seral habitat.

The owl conservation strategy is to be completed by March 31, 2016. The owl and fisher conservation strategies are to be included as alternatives in the draft EIS's for the new forest plans. The agency was also tasked with creating "interim recommendations on changes in forest management" to conserve the owl. These conditions have been partially met with the May 29, 2015 draft California Spotted Owl Interim Recommendations for Management. These guidelines will serve as an interim strategy until the final conservation strategy is completed. The region has made clear in this February 12, 2016 letter to the forest supervisors that the draft recommendations are to be treated as the "final" recommendations.

SFL is currently examining projects that are being proposed in spotted owl habitat to determine if they are consistent with the interim management recommendations. Download and read our scoping comments on these projects, below:

DEIS for Trestle Forest Health Project, August 31, 2015

Cuckoo Vegetation Management and Fuels Reduction Project, September 21, 2015

Summit Fuels Reduction and Forest Health Project, October 12, 2015

Lakes Basin Project, December 16, 2015

Forbestown Community Protection Fuels Reduction Project, February 8, 2016

Panther Fuels Reduction and Forest Health Project, March 8, 2016

 

September 18, 2015

Female California Spotted Owl by Sheila WhitmoreToday the U.S. Fish and Wildlife Service issued a positive 90-day finding on a petition submitted by Wild Nature Institute and the John Muir Project of the Earth Island Institute to list the California spotted owl under the federal Endangered Species Act (submitted December 22, 2014). 

On August 19, 2015, Sierra Forest Legacy and Defenders of Wildlife filed another petition to list the California spotted owl under the Endangered Species Act.

Image left: Female California Spotted Owl, by Sheila Whitmore, courtesy SNAMP

Since 2006, a substantial body of scientific literature has been published that calls into question the basis of the USFWS’s 2006 decision not to list the species, including:  (1) conclusive evidence of a range-wide decline in California spotted owl abundance and occupancy on all Forest Service-managed lands that have been monitored for more than 20 years (Conner et al. 2013; Tempel and Gutiérrez 2013; Tempel et al. 2014b); (2) correlation between activities that reduce canopy cover (i.e., Forest Service fuels treatments) and reduced colonization, reproduction, increased territory sizes, and increased territory abandonment probabilities (Seamans and Gutiérrez 2007; Gallagher 2010, Stephens et al. 2014; Tempel et al. 2014a); (3) wildfire within territories has had no discernable effect on occupancy throughout the Sierra Nevada (Lee et al. 2012); (4) low and moderate severity burned forests maintain essential habitat characteristics and do not affect occupancy (Roberts et al. 2011); (5) mixed and high severity burned forests are used for foraging and do not represent a categorical loss of habitat (Bond et al. 2009b, Bond et al. 2013); and (6) post-fire management practices (i.e., salvage logging and industrial reforestation) on public and private lands results in the long-term degradation of foraging habitat and nesting and roosting habitat.  These new data represent substantial new information on the biology, demographic trends, and threats to the species that significantly changes our understanding of the status and threats to the California spotted owl, and indicate the species is likely to become endangered or extinct in the foreseeable future.

Read the latest petition, and additional history and background information here.

Or download the petition now: Sierra Forest Legacy and Defenders of Wildlife Petition to list the California Spotted Owl under the Endangered Species Act, August 19, 2015

Read more about the owl's habitat, range, threats, and conservation status, below.

Range and Distribution

In the Sierra Nevada, the range of the California spotted owl spans from approximately 24 km south of the Pit River in the southern Cascades (Barrowclough et al. 2011) to Tehachapi Pass (Verner et al. 1992), including the entire western side of the Sierra Nevada from about 1,000 to 8,000 feet in elevation. There are several scattered territories on the east side of the Sierra Nevada crest, primarily in the northern and central portions of the mountain range, from about 5,500 to 8,000 feet elevation. The California spotted owl also occupies forested habitat in all of the major mountain ranges of southern California and the Southern Coast Range as far north as Monterey County. However, these mountain ranges consist of isolated islands of forest habitat, surrounded by low elevation desert scrub, chaparral, and urbanization, conditions not known to support breeding or foraging.  Compared to the northern or Mexican spotted owls, two spotted owl subspecies listed by the USFWS as threatened, the range of the California spotted owl is approximately one quarter or less the area (Gutiérrez and Harrison 1996).

Habitat

There is relative scientific consensus that high quality nesting and roosting habitat consists of multi-layered forest stands dominated by large diameter trees (greater than 24 inches diameter), with forest canopy cover greater than 70 percent, and numerous large snags and large downed logs. The average size of a nest stand was found to be 99 acres on the Sierra National Forest.  Activity centers (i.e., the area containing 50 percent of radio telemetry locations) were found to be about 300 acres on the Sierra National Forest (Verner et al. 1992). However, due to differences in climate, topography, and forest composition between the northern, central, and southern Sierra Nevada, the sizes of the activity center, territory, and home range in the southern Sierra are the smallest recorded in the mountain range. In contrast to the 300-acre activity centers observed on the Sierra National Forest, activity centers on the Lassen National Forest in the northern Sierra Nevada averaged 788 acres (Verner et al. 1992).

California spotted owl territory sizes average about 800 acres on the Sierra, 1,000 acres on the Eldorado, and 2,400 on the Lassen National Forests. In addition to nesting and roosting habitat, territories and home ranges must provide an adequate quantity of high quality foraging habitat.  Spotted owls primarily prey on flying squirrels and woodrats. Within the range of the California spotted owl, flying squirrels are often associated with moist large conifer stands, and woodrats are often associated with forests that contain an oak and shrub component.

California spotted owl foraging habitat is typically composed of multi-layered canopied forests with at least 40 to 50 percent canopy cover dominated by medium and large trees, with high numbers of large snags and large downed logs (Verner et al. 1992).  Although California spotted owls will forage in stands with canopy cover as low as 40 to 50 percent, stands with this level of canopy cover do not necessarily provide high quality foraging habitat capable of maintaining territory occupancy or successful reproduction.  Studies suggest that mechanical reductions in canopy cover to below 70 percent within territories increases the probability of dispersal (Seamans and Gutierrez 2007), reduces survival, reduces colonization, and increases territory extinction probabilities (Tempel et al. 2014b).

While it is still believed that spotted owls require high canopy cover forest stands or patches for nesting in burned and unburned forests, several studies have been published that suggest that in the absence of post-fire salvage logging in forests that have burned at low and moderate severity, California spotted owls continue to use these habitats for foraging, and such burn severities do not appear to affect occupancy as many as 14 years post-fire.  Bond et al. (2009) also found that for five of the seven spotted owls in the study, the strongest selection for foraging was in high-severity burned forest within 1.5 kilometers of the territory center. Interestingly, Bond et al. (2013) found that pocket gophers were a major prey item of spotted owls in burned forests in the southern Sierra Nevada, representing a much larger proportion of their diet than recorded anywhere in unburned forests. 

Demographic Trends

The USFWS’s 2006 finding that the species did not warrant ESA protections relied heavily on a draft demographic meta-analysis conducted by Blakesley et al. (2006). Since 2006, several long-term demographic studies have been published that suggest the statistical methods of Blakesley et al. (2006) lacked the statistical power to detect the ongoing declines. These new studies affirm that declines have occurred on all Forest Service-managed lands with long-term survey data over the past 20-plus years, and the only stable or increasing population is in Sequoia-Kings Canyon National Park where logging does not occur. Specifically, between 1990 and 2012, the spotted owl population declined by 50 percent in the Eldorado demographic study area (Tempel et al. 2014b). From 1993 to 2010, spotted owl occupancy declined by 30 percent, territory extinction increased over time, and colonization rates were insufficient to maintain occupancy at its initial level on the Eldorado study area (Tempel and Gutiérrez 2013). Over the 18-year study period, the population declined by 21 to 22 percent in the Lassen and 11 to 16 percent in the Sierra demographic study areas, and increased by 16 to 27 percent in the Sequoia-Kings Canyon National Park demographic study area (Conner et al. 2013). It is important to note that from the early 1990s through 2012 there was very little to no high severity wildfire activity within the four demographic study areas, suggesting that the observed declines were unrelated to the effects of wildfire or post-fire salvage logging. 

Threats

California spotted owl by Marek Jakubowski via SNAMPThe California spotted owl is closely associated with old forests and according to studies, old-growth forests in the Sierra Nevada have declined by as much as 90 percent. Measures taken by Federal land managers over the last two decades have failed to show marked improvement in its status.

Photo right: California Spotted Owl in cedar by Marek Jakubowski via SNAMP.

There are several interacting threat factors acting on the California spotted owl that cause significant concern for the species' ability to persist over the long-term throughout its current range. These threats include:  (1) Mechanical Thinning to Harvest Timber on Public Land (2) Industrial Timber Harvest on Private Land; (3) Post-Disturbance Logging on Public and Private Land; (4) High Severity Fire in Nesting and Roosting Habitat; (5) Urbanization and Development; (6) Climate Change; and (7) Competition with Barred Owl.

Recently published research has consistently documented a correlation between mechanical reductions in canopy cover and adverse effects to California spotted owl:

  • Alteration of 50 acres or more of mature conifer forest (conifer forest with greater than 70 percent canopy cover dominated by medium and large trees) within a spotted owl territory increased dispersal probability (Seamans and Gutiérrez 2007).
  • Home range size increased with the amount of fuels treatment within the home range (Gallagher 2010).
  • Medium-intensity timber harvests, characteristic of proposed fuel treatments, were negatively related to reproduction of spotted owls, with reproduction appearing sensitive to modest amounts of medium-intensity harvests (Tempel et al. 2014a).
  • Reductions in canopy cover were associated with reductions in spotted owl survival and territory colonization rates, as well as increases in territory extinction rates (Tempel et al. 2014a).
  • Greater than 90% of medium intensity harvests converted high-canopy forests into lower-canopy vegetation classes, suggesting that landscape-scale fuel treatments could have negative impacts on populations of California spotted owls (Tempel et al. 2014a).
  • The effects of implementing fuels treatments immediately decreased average habitat suitability, with a difference still present after 30 years of simulated forest growth (SNAMP 2015).

Even-aged management on Forest Service lands was ended to protect spotted owls as a result of the spotted owl assessment conducted by Verner et al. (1992).  Since that time, the best available science continues to suggests that spotted owls select for large blocks of mature forest with dense canopy cover (greater than 70 percent) (Seamans and Gutierrez 2007), nest farther from high contrast edges than chance alone (e.g., edges created by even-aged management) (Phillips et al. 2010), and are more likely to select public land than private land for foraging (Williams et al. 2014).  As a result, private timber harvest activities likely reduce the quality and quantity of nesting, roosting, and foraging habitat and increase dispersal probability.  Industrial timber lands were included in the modeling done by Seamans and Gutiérrez (2007), suggesting that reductions in canopy cover on industrial timber lands were at least partially responsible for the increased probability of female breeding dispersal. 

The structural complexity of post-fire forests, compared to salvage- or clear cut-logged forests, is extremely high and spatially heterogeneous due to the presence of scattered pockets of surviving trees, substantial levels of native shrubs and sprouting hardwood trees, and high levels of woody legacies, such as snags and downed boles (Swanson et al. 2010).  Stand-replacement fires provide large pulses of coarse woody debris, including snags and logs, which lifeboat dependent species, including many species spotted owls prey on, until the regenerating forest begins to produce large and decay-resistant dead wood structures, which is typically not for a century or more (Franklin 2015).  While there is likely a threshold at which the amount of high severity burned forest within a spotted owl territory in the Sierra Nevada significantly increases the likelihood of territory abandonment and reduces potential reproductive output in the years following fire, such a threshold has not been established.  However, evidence from Lee et al. (2012) indicates that such a threshold is greater than 32 percent of a spotted owl territory burning at high severity.

We now know that spotted owls use forests that burn at all severities for foraging (Bond et al. 2009) and forests that burn at low and moderate severity have no effect on spotted owl occupancy and retain essential habitat characteristics (Roberts et al. 2011).  However, most wildfires in the Sierra Nevada that affect accessible timber lands are salvage-logged, including forest that burn at low and moderate severity.  Mounting scientific evidence supports the conclusion that salvage logging adversely affects habitat at a landscape scale and poses a significant threat to the species.  Lee et al. (2013) found that compared with unlogged burned sites, salvage-logged sites had greater extinction probabilities which further reduced site occupancy.  Clark et al. (2013) found that occupancy of nesting territories by northern spotted owls in southern Oregon declined after fires because extinction probabilities increased as the combined area of high severity burned forest, salvage logging, and early seral forest (i.e., pre-fire clear cuts) increased.  It is perplexing that the Forest Service justifies thinning as a tool to mimic natural fire patterns, but when wildfires or a portion of a wildfire burns within the natural range of variation, the agency salvage logs the restorative effects of the fire.

In the USFWS’s 2006 finding that the species did not warrant protections under the Endangered Species Act, the agency contended that high severity fire represented the greatest threat to the species, Forest Service thinning ameliorated the threat of high severity fire, and commercial timber harvests do not represent a threat to the species.  We conducted a GIS analysis for or listing petition to test USFWS’s justification.  We found that the total number of acres with Timber Harvest Plans and Forest Service management activities likely to significantly reduce canopy cover within 0.7 mile of spotted owl territory centers since 2006 in the Sierra Nevada was 197,549 acres (Table 1), over twice the total number of acres within 0.7 mile of spotted owl territory centers that burned at high severity since 2006 (90,584 acres); suggesting that timber harvests on public and private lands represent a much greater threat to spotted owls in the Sierra Nevada bioregion than high severity fire. 

Table 1.  Cumulative area (acres) of disturbance within spotted owl territories (n = 2,002; 0.7 mile radius from an activity center) in the Sierra Nevada bioregion.  Disturbances evaluated include Timber Harvest Plans (THP) approved and/or completed from 2006 to 2013, U.S. Forest Service activities completed since 2006 that are likely to reduce canopy cover, and the amount of high severity fire.

 

Conservation

In the early 1990’s the Forest Service in California began considering strategies that would improve conservation for California spotted owls, while providing for management flexibility. Figuring the California owl would follow the trajectory of federal listing as the northern and Mexican spotted owls, the Forest Service commissioned a technical assessment of the status of the California spotted owl, including recommendations to minimize threats.  The California Spotted Owl: A Technical Assessment of Its Current Status (Verner et al. 1992), was issued by a team of scientists (Pacific Southwest Research Station General Technical Report, or PSW-GTR-133) . 

Verner et al. (1992) understood the concepts of heterogeneity and the role that low and mixed severity fire should play in forest restoration at a time when those concepts were not part of the forest management vernacular.  Unfortunately, over the past 23 years managers have avoided the use of prescribed fire and continued to suppress virtually all fire, preferring timber harvests designed to result in homogenous stand structures that maximize wood volume growth rates at the expense of habitat complexity and spotted owl viability. The majority of thinning projects have and continue to reduce canopy cover to the lowest allowable limit. 

The 2001 Sierra Nevada Framework Plan paid particular attention to the spotted owl decline by crafting a set of standards to protect its habitat. The Forest Service’s 2004 revisions to the Framework eliminated the key protection measures for medium and large trees, canopy cover, home-range core areas and weakened protections near nests. The original Framework provided protection for the owl, while at the same time allowing for substantial progress towards reducing risk of destructive forest fires, by protecting fire resistant medium and large trees across the landscape, and focusing fuel treatments around communities where they are needed most.

The U.S. Fish and Wildlife Service’s original decision (In 2003, see below) not to list the owl under the Endangered Species Act was based on the assumption that the owl’s habitat in the Sierra Nevada would be largely protected by the Clinton Administration’s Sierra Nevada Framework, a plan that restricted logging to protect the owl’s habitat. However, once the Bush Administration’s revisions of the Sierra Nevada Framework were adopted in 2004, promising to triple logging in the Sierra Nevada, the Fish and Wildlife again denied endangered status to the owl.

As a result of our settlement agreement with the Forest Service over the 2004 Sierra Nevada Forest Plan Amendment, and data suggesting there is a Forest Service-wide California spotted owl decline and that the decline is correlated with fuels treatments, the Forest Service commissioned a team of scientists to provide interim recommendations on changes to forest management.  In May of 2015, draft interim recommendations were released that constitute a suite of measures that individually hold promise and support in scientific literature pertaining to spotted owls and forest ecology.  The interim recommendations focus on maintaining adequate amounts of high canopy cover forest within spotted owl territories and using fire as the primary management tool to reduce fuel loading and increase resilience to wildfire within territories. As part of our settlement agreement, the interim recommendations must be used to develop an alternative in all relevant planning documents.  The Forest Service is currently working on a California spotted owl conservation strategy that will supersede the interim recommendations when complete. 

Status

Sierra Forest Legacy filed a new petition, on August 19 2015, to list the California spotted owl under the Endangered Species Act. In December 2014, Wild Nature Institute and the John Muir Project of the Earth Island Institute also filed a petition, with an emphasis on recent research suggesting that large wildfires are not as harmful to the owl as previously thought. Our position is somewhat more nuanced, due to the fact that forests are almost always logged heavily after large wildfires, effectively erasing any potential ecological benefits from such fires. In either case, the owl is certainly imperiled by the condition of our forests in the Sierra Nevada today. Currently, the US FWS is evaluating the owl under the 12-month status review, after which it will determine whether or not the owl requires protection under the Endangered Species Act.

In April of 2000, the Sierra Forest Protection Campaign (now Sierra Forest Legacy) and the Center for Biological Diversity filed the first petition to list the California Spotted Owl under the Endangered Species Act. In 2003 the U.S. Fish and Wildlife Service denied that listing, stating there was inconclusive evidence for the owl's decline. A second petition to list was filed in 2004 after the revisions to the Sierra Nevada Framework were adopted and the Fish and Wildlife Service once again denied listing. The California Spotted owl is consider a “sensitive” species by the Forest Service though this status has done little to stop projects and plans which greatly impact the habitat of the owl and its survivability in the Sierra Nevada. Meanwhile, unprecedented levels of clearcutting have since consumed hundreds of thousands of owl habitat in the surrounding industrial timber lands in the Sierra Nevada.

The Forest Service was required to monitor the California spotted owl under the terms of the 2004 Framework Appeal decision that established an adaptive management program incorporating Appendix E, the monitoring program established for the new Framework (2001 and 2004). The Region's committments include funding on-going monitoring of the Pacific fisher, American marten, and the California spotted owl. The monitoring program, Sierra Nevada Adaptive Monitoring Program (SNAMP) ended in 2015. You can read the final reports at this link.

Monitoring in the Plumas Lassen Study Area reports owl declines over the last 20 years, and in October 2012, the Sierra Nevada Adaptive Management Program owl research team reported steady declines, in the Eldorado Study Area and the Sierra National Forest. Population declines appear to be as high as 50 percent in the Eldorado Study Area. This is significant new information, since it now appears that data had been misinterpreted, or at the least was too imprecise, when F&WS was evaluating the owl for potential listing under the Endangered Species Act.

Click here to view an online webinar presented by owl scientist John Keane (April, 2012). This webinar is sponsored by the California Fire Science Consortium. Keane discusses recent research investigating the effects from fuels treatments and wildfires on California spotted owls and their habitat in the Plumas-Lassen Study Area, as well as other related topics. Researchers are attempting to monitor the effects of fuels treatments implemented under the Herger-Feinstein Quincy Library Group Act in the northern Sierra Nevada. Keane reports the decline of the California spotted owl in three of the four study areas: Plumas-Lassen, Eldorado, and Sierra National Forest Study Areas; while the owls are holding steady on the Sequoia Kings Canyon National Park study area.

Click here to view a slide show presentation by owl scientist Doug Tempel, documenting the serious decline of the owl in the El Dorado Study Area.

Click here to view California Spotted Owl Species Assessment and Conservation Measures from SFL's Conservation Strategy.

Below, you can watch a video created by the SNAMP owl team that highlights ongoing California spotted owl research.


Scientific Research and Reports

Barrowclough, G.F., R.J. Gutiérrez, J.G. Groth, J.E. Lai, and D.F. Rock.  2011.  The hybrid zone between northern and California spotted owls in the Cascade-Sierran suture zone.  The Condor 113:581-589 (234 KB PDF).

Bart, J., and E.D. Forsman. 1992. Dependence of Northern Spotted Owls Strix Occidentalis Caurina on Old-Growth Forests in The Western U.S.A. Biological Conservation 62, 95-100 (470KB PDF)

Blakesley J.A., B.R. Noon and D. W. H. Shaw. 2001. Demography of the California Spotted Owl in Northeastern California. The Condor 103(4) 667–677. (132KB PDF)

Blakesley, J.A. 2003. Ecology of the California Spotted Owl: Breeding Dispersal and Associations With Forest Stand Characteristics in Northeastern California. Ph.D. Dissertation, Colorado State University, 69 Pp. (12.35MB PDF)

Blakesley, J.A., B.R. Noon and D.R. Anderson. 2005. Site Occupancy, Apparent Survival, and Reproduction of California Spotted Owls in Relation to Forest Stand Characteristics. Journal of Wildlife Management 69(4)1554–1564. (118KB PDF)

Blakesley, J.A., D.W.H. Shaw  and B.R. Noon. 2005. Ecology of the California Spotted Owl on The Lassen National Forest, 1990-2004; Final Report. Colorado State University. Fort Collins, Colorado. (242KB PDF)

Blakesley, J.A., D.R. Anderson and B.R. Noon. 2006. Breeding Dispersal in the California Spotted Owl. The Condor 108, 71–81 (120KB PDF)

Blakesley, J. A., M .E. Seamans, M. M. Conner, A. B. Franklin, G. C. White, R. J. Gutiérrez, J. E. Hines, J. D. Nichols, T. E. Munton, D. W. H. Shaw, J. J. Keane, G. N. Steger, B. R. Noon, T. L. McDonald, and S. Britting.  2006.  DRAFT Demography of the California spotted owl in the Sierra Nevada:  Report to the U. S. Fish and Wildlife Service on the January 2006 meta-analysis.  February 21, 2006.  106 pages. (529 KB PDF)

Blakesley, J. A., M .E. Seamans, M. M. Conner, A. B. Franklin, G. C. White, R. J. Gutiérrez, J. E. Hines, J. D. Nichols, T. E. Munton, D. W. H. Shaw, J. J. Keane, G. N. Steger, and T. L. McDonald.  2010.  Population dynamics of spotted owls in the Sierra Nevada, California.  Wildlife Monographs 174: 1–36. (1.23 MB PDF)

Bond, M.L., R.J. Guttierez, A.B. Franklin, W.S. LaHaye, C.A. May, M.E. Seamans. 2002. Short-term Effects of Wildfires on Spotted Owl Survival, Site Fidelity, Mate Fidelity, and Reproductive Success. Wildlife Society Bulletin, 30(4) 1022-1028. (641KB PDF)

Bond, M.L., M.E. Seamans, and R.J. Guitierrez. 2004. Modeling Nesting Habitat Selection of California Spotted Owls (Strix occidentalis occidentalis) in the Central Sierra Nevada Using Standard Forest Inventory Metrics. Forest Science, 56(6) 773-780. (89KB PDF)

Bond, M.L., D.E. Lee, C.M. Bradley, and C.T. Hanson. 2009. Influence of pre-fire tree mortality on fire severity in conifer forests of the San Bernardino Mountains, California. Open Forest Science Journal. 2009,2, 41-47 (919 KB PDF)

Bond, M.L., D.E. Lee, R.B. Siegel, and J.P. Ward.  2009.  Habitat use and selection by California spotted owls in a postfire landscape.  Journal of Wildlife Management 73:1116-1124 (283 KB PDF)

Bond, M.L., D.E. Lee, and R.B. Siegel.  2010.  Winter movements by California spotted owls in a burned landscape.  Western Birds 41:174-180 (66 KB PDF)

Bond, M.L., D.E. Lee, R.B. Siegel, and M.W. Tingley.  2013.  Diet and home-range size of California spotted owls in a burned forest.  Western Birds 44:114-126 (435 KB PDF) 

Call, D.R., R.J. Gutiérrez, and J. Verner.  1992.  Foraging habitat and home-range characteristics of California spotted owls in the Sierra Nevada.  The Condor 94:880-888 (3.46 MB PDF)

Chatfield, A.H. 2005. Habitat Selection by a California Spotted Owl Population: A Landscape Scale Analysis Using Resource Selection Functions. Master of Science Thesis, University Of Minnesota. St. Paul, Minnesota. (1.12MB PDF)

Clark, D.A., R.G. Anthony, and L.S. Andrews.  2013.  Relationship between wildfire, salvage logging, and occupancy of nesting territories by northern spotted owls.  Journal of Wildlife Management 77:672-688 (1.03 MB PDF)

Conner, M. M., J. J. Keane, C. V. Gallagher, G. J. Jehle, T. E. Munton, P. A. Shaklee, and R. A. Gerrard.  2013.  Realized population change for long-term monitoring:  California spotted owl case study.  Journal of Wildlife Management 77: 1449-1458. (954 KB PDF)

Conner, M. M., J. J. Keane, C. V. Gallagher, T. E. Munton, and P. A. Shaklee. 2016. Comparing estimates of population change from occupancy and mark–recapture models for a territorial species. Ecosphere 7(10):e01538. 10.1002/ecs2.1538 (652 KB).

Dawson, W. et al. 1987. Report of the scientific advisory panel on the spotted owl. Condor. 89:205-229. (2.4 MB PDF)

Dolanc, C.R., H.D. Safford, J.H. Thorne, and S.Z. Dobrowski. 2014. Changing forest structure across the landscape of the Sierra Nevada, CA, since the 1930s. Ecosphere 5(8):101. http://dx.doi.org/10.1890/ES14-00103.1 (1.14 MB PDF)

Dugger, K.M., R.G. Anthony, and L.S. Andrews.  2011.  Transient dynamics of invasive competition: barred owls, spotted owls, habitat, and the demons of competition present.  Ecological Applications 21:2459-2468 (418 KB PDF)

Eyes, S.A.  2014.  The effects of fire severity on California spotted owl habitat use patterns. M.S. Thesis, Humboldt State University, Arcata, California (884 KB PDF)

Franklin, A.B., D. R. Anderson, R. J. Gutierrez, and K.P. Burnham. 2000. Climate, Habitat Quality, and Fitness in Northern Spotted Owl Populations in Northwestern California. Ecological Monographs 70(4) 539–590. (679KB PDF)

Franklin, A.B. et al. 2003. Population Dynamics of the California Spotted Owl: A Meta-Analysis. Final report to the U.S. Forest Service Pacific Southwest Research Station. Berkeley, CA. (1.13 MB PDF)

Franklin, A. B., R. J. Gutiérrez, J. D. Nichols, M. E. Seamans, G. C. White, G. S. Zimmerman, J. E. Hines, T. E. Munton, W. S. LaHaye, J. A. Blakesley, G. N. Steger, B. R. Noon, D. W. H. Shaw, J. J. Keane, T. L. McDonald, and S. Britting.  2004.  Population dynamics of the California Spotted Owl (Strix occidentalis occidentalis):  A meta-analysis.  Ornithological Monographs 54:  1-54. (2.6MB PDF)

Gallagher, C.V.  2010.  Spotted owl home range and foraging patterns following fuels-reduction treatments in the northern Sierra Nevada, California.  M.S. Thesis, University of California Davis (1.12 MB PDF)

Gutierrez, R.J., and G.F. Barrowclough. 2005. Redefining the Distributional Boundaries of the Northern and California Spotted Owls: Implications For Conservation. The Condor 107:182–187. (522KB PDF)

Gutiérrez, R.J., W.S. LaHaye, and G.S. Zimmerman.  2011.  Breeding dispersal in an isolated population of spotted owls Strix occidentalis: evidence for improved reproductive output.  Ibis 153:592-600 (147 KB PDF)

Keane, J. Gallagher, C.V., Gerrard, R. A., Jehle, G., and Shaklee, P. A. 2011. Chapter 5: Spotted Owl Module. In: Plumas Lassen Study. 2010 Annual Report. USDA Forest Service Pacific Southwest Research Station. (5.33 MB PDF)

Keane, J.J.  2014.  California spotted owl: Scientific considerations for forest planning. Pages 437–467 in Long J.W., L. Quinn-Davidson, and C.N. Skinner eds. Science Synthesis to Support Socioecological Resilience in the Sierra Nevada and Southern Cascade Range. U.S. Department of Agriculture. General Technical Report no. PSW-GTR-247 (336 KB PDF)

Kelly, E.G, and E.D. Forsman. 2004. Recent Records of Hybridization Between Barred Owls (Strix Varia) and Northern Spotted Owls (S. Occidentalis Caurina). The Auk 121(3) 806–810. (59KB PDF)

Irwin L.L., L.A. Clark, D.C. Rock, and S.L. Rock.  2007.  Modeling foraging habitat of California spotted owls.  Journal of Wildlife Management 71:1183-1191 (147 KB PDF)

LaHaye, W.S., R.J. Gutierrez, and J.R. Dunk. 2001. Natal Dispersal of the Spotted Owl in Southern California: Dispersal Profile of an Insular Population. The Condor 103, 691–700 (98KB PDF)

LaHaye, W.S., and R.J. Gutiérrez.  2005.  The spotted owl in southern California: ecology and special concerns for maintaining a forest-dwelling species in a human-dominated desert landscape.  USDA Forest Service.  General Technical Report PSW-GTR-195 (560 KB PDF)

LaHaye, W.S., R. J. Gutierrez, and G.S. Zimmerman. 2004. Temporal Variation in the Vital Rates of an Insular Population of Spotted Owls (Strix Occidentalis Occidentalis): Contrasting Effects of Weather. The Auk 121(4) 1056–1069. (160KB PDF)

Laymon, S.A.  1988.  Ecology of the spotted owl in the central Sierra Nevada, California.  Dissertation, University of California, Berkeley, California (5.87 MB PDF)

Lee, D.C., and L.L. Irwin. 2005. Assessing Risks to Spotted Owls From Forest Thinning in Fire-Adapted Forests of the Western United States. Forest Ecology and Management 211, 191–209. (772KB PDF)

Lee, D.E., M.L. Bond, and R.B. Siegel.  2012.  Dynamics of breeding-season site occupancy of the California spotted owl in burned forests.  The Condor 114:792-802  (316 KB PDF)

Lee, D.E., M.L. Bond, M.I. Borchert, and R. Tanner.  2013.  Influence of fire and salvage logging on site occupancy of spotted owls in the San Bernardino and San Jacinto mountains of southern California.  Journal of Wildlife Management 77:1327-1341  (751 KB PDF)

Lee, D.E., and M.L. Bond.  2015.  Occupancy of California spotted owl sites following a large fire in the Sierra Nevada, California.  The Condor 117:228-236 (192 KB PDF)

MacKenzie, D. I., J. D. Nichols, J. E. Hines, M. G. Knutson, and A. B. Franklin.  2003.  Estimating site occupancy, colonization, and local extinction when a species is detected imperfectly.  Ecology 84:2200-2207. (102 KB PDF)

MacKenzie, K.I., M.E. Seamans, R.J. Gutiérrez, and J.D. Nichols.  2010.  Investigating the population dynamics of California spotted owls without marked individuals.  Journal of Ornithology DOI 10.1007/s10336-010-0544-6 (308 KB PDF)

Munton, T.E., K.D. Johnson, G.N. Steger, and G.P, Eberlin. 2002. Diets of California Spotted Owls in the Sierra National Forest. Proceedings of a Symposium on The Kings River Sustainable Forest Ecosystem Project: Progress and Current Status. Gen. Tech. Rep. PSW-GTR-183, Albany, CA: Pacific Southwest Research Station, U.S. Forest Service. Pp. 99-106. (264KB PDF)

Noon, B.R., and A.B. Franklin. 2002. Scientific Research and the Spotted Owl (Strix Occidentalis): Opportunities for Major Contributions to Avian Population Ecology. The Auk 119(2) 311–320. (94KB PDF)

North, M., G. Steger, R. Denton, G. Eberlin, T. Munton, and K. Johnson. 2000. Association of Weather and Nest-Site Structure with Reproductive Success in California Spotted Owls. Journal of Wildlife Management 64(3) 797-807. (942KB PDF)

Peery, M.Z., and R.J. Gutiérrez.  2013.  Life-history tradeoffs in spotted owls (Strix occidentalis): implications for assessment of territory quality.  The Auk 130:132-140 (275 KB PDF).

Peterson, A.T., and C.R. Robins. 2003. Using Ecological-Niche Modeling to Predict Barred Owl Invasions with Implications for Spotted Owl Conservation. Conservation Biology 17(4) 1161-1165. (1.23MB PDF)

Phillips C.E., D.J. Tempel, and R.J. Gutiérrez.  2010.  Do California spotted owls select nest trees close to forest edges?  Journal of Raptor Research 44:311-314 (1.09 MB PDF)

Roberts, S.L., van Wagtendonk, J.W., Miles, A.K., and Kelt, D.A. 2011. Effects of fire on spotted owl site occupancy in a late-successional forest. Biological Conservation 144:610-619. (600KB PDF)

Roberts, S.L., D.A. Kelt, J.W. van Wagtendonk, A.K. Miles, and M.D. Meyer.  2015.  Effects of fire on small mammal communities in frequent-fire forests in California Journal of Mammalogy 96:107-119 (2.52 MB PDF).

Seamans, M.E. 2005. Population Biology of the California Spotted Owl in the Central Sierra Nevada. Ph.D. Dissertation. University Of Minnesota. St. Paul, Minnesota. (1.3MB PDF)

Seamans, M. E., and R. J. Gutierrez.  2007.  Habitat selection in a changing environment:  the relationship between habitat alteration and spotted owl territory occupancy and breeding dispersal.  Condor 109:566-576. (301 KB PDF)

Steger, G.N., T.E. Munton, K.D. Johnson, and G.P Eberlin. 2002. Demography of the California Spotted Owl in the Sierra National Forest and Sequoia/Kings Canyon National Park. Proceedings of a Symposium on The Kings River Sustainable Forest Ecosystem Project: Progress And Current Status. Gen. Tech. Rep. PSW-GTR-183, Albany, CA: Pacific Southwest Research Station, U.S. Forest Service. 107-116. (637KB PDF)

Steger, G.N., T.E. Munton, K.D. Johnson, and G.E. Eberlin. 1997. Characteristics of California Spotted Owl Nest Sites in Foothill Riparian and Oak Woodlands of the Southern Sierra Nevada, California. U.S. Forest Service Gen. Tech. Rep. PSW-GTR-160. (133KB PDF)

Steger, G.N., T.E. Munton, K.D. Johnson, and G.E. Eberlin. 1997. Characteristics of Nest Trees and Nest Sites of California Spotted Owls in Coniferous Forests of the Southern Sierra Nevada. Transactions of the Western Section of the Wildlife Society 33:30-3. (954KB PDF)

Stephens, S.L., J.D. Miller, B.M. Collins, M.P. North, J.J. Keane, and S.L. Roberts. 2016. Wildfire impacts on California spotted owl nesting habitat in the Sierra Nevada. Ecosphere 7(10):e01478. 10.1002/ecs2.1478 (1.84 MB PDF)

Tempel, D.J. 2014. California Spotted Owl Population Dynamics in the Central Sierra Nevada:  An Assessment Using Multiple Types of Data. PhD Dissertation, University of Minnesota. (508 KB PDF)

Tempel, D.J., and R.J. Gutierrez. 2004. Factors Related to Fecal Corticosterone Levels in California Spotted Owls: Implications for Assessing Chronic Stress. Conservation Biology 18(2) 538-547. (211KB PDF)

Tempel, D.J., and R.J. Gutierrez.  2013.  Relationship between occupancy and abundance for a territorial species, the California spotted owl.  Conservation Biology 00:1-9. (474 KB PDF)

Tempel, D.J., R.J. Gutierrez, S.A. Whitmore, M.J. Reetz, R.E. Stoelting, W.J. Berigan, M.E. Seamans, M.Z. Peery. 2014. Effects of forest management on California Spotted Owls: implications for reducing wildfire risk in fire-prone forests. Ecological Applications 24:2089–2106 (508 KB PDF)

Tempel, D.J., M.Z. Peery, and R.J. Gutiérrez.  2014.  Using integrated population models to improve conservation monitoring: California spotted owls as a case study.  Ecological Modelling 289:86-95 (932 KB PDF)

Tempel, D.J. et al. 2016. Meta-analysis of California Spotted Owl (Strix occidentalis occidentalis) territory occupancy in the Sierra Nevada: Habitat associations and their implications for forest management. The Condor 118(4):747-765. (743 KB PDF)

Thompson, C., R. Sweitzer, M. Gabriel, K. Purcell, R. Barrett, and R. Poppenda.  2014.  Impacts of rodenticide and insecticide toxicants from marijuana cultivation sites on fisher survival rates in the Sierra National Forest, California.  Conservation Letters 7: 91-102.

Washburn, B.E., et.al. 2004. Factors Related to Fecal Estrogens and Fecal Testosterone in California Spotted Owls. The Condor 106, 567–579 (118KB PDF)

Weathers, W.W., P.J. Hodum, and J.A. Blakesley. 2001. Thermal Ecology and Ecological Energetics of California Spotted Owls. The Condor 103:678–690. (122KB PDF)

Williams, P.J., R.J. Gutiérrez, and S.A. Whitmore.  2011.  Home range and habitat selection of spotted owls in the central Sierra Nevada.  Journal of Wildlife Management 75:333-343. 

Williams, P.J., S.A. Whitmore, and R.J. Gutiérrez.  2014.  Use of private lands for foraging by California spotted owls in the central Sierra Nevada.  Wildlife Society Bulletin 38:705-709.

Zielinski, W.J., C. Carroll, and J.R. Dunk. 2006. Using Landscape Suitability Models to Reconcile Conservation Planning for two key Forest Predators. Biological Conservation. 2006. (2.33MB PDF)

Zimmerman, G.S., W.S. LaHaye, and R.J. Gutierrez. 2003. Empirical Support for a Despotic Distribution in a California Spotted Owl Population. Behavioral Ecology 14(3) 433–437. (103KB PDF)

Verner, J., K.S. McKelvey, B.R. Noon, R. J. Gutiérrez, G.I. Gould, Jr., and T.W. Beck. 1992. The California Spotted Owl: A Technical Assessment of Its Current Status. GTR 133. Pacific SW Research Station U.S. Forest Service (8.40 MB PDF) (Click here to go to website to download individual chapters)


Supporting Resources

USFS 90-day Finding on Petition to List California Spotted Owl under Endangered Species Act.

Sierra Forest Legacy and Defenders of Wildlife Petition to List the California Spotted Owl under the Endangered Species Act, August 19, 2015.

Wild Nature Institute and John Muir Project Petition to List the California Spotted Owl under the Endangered Species Act, Dec. 22, 2014 (external link).

2015 SNAMP (Sierra Nevada Adaptive Management Program). Draft Sierra Nevada Adaptive Management Program Final Report:  Appendix C. California Spotted Owl Team Report (4.71 MB PDF)r

2011 Sierra Forest Legacy Letter to Forest Service Region 5 (117 KB PDF)

2006 USFWS 12 month finding of not warranted (154KB PDF)

2004 Updated petition to list as threatened or endangered (1.13MB PDF)

2003 USFWS 12 month finding of not warranted (170KB PDF)

2003 Conservation Organizations Notice of Petition to List (99KB PDF)

2000 Petition to list under Endangered Species Act (531KB PDF)

California Department of Fish and Game Natural History Information --This California state website contains rather limited and old information but is a good basic background composite for the species. Choose from a drop-down list to select the animal you are interested in.


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