Strix occidentalis caurina

Temperate forests from s British Columbia to n California.

Old growth forests in British Columbia, Washington, Oregon, and northern California

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (200,000-2,500,000 square km (about 80,000-1,000,000 square miles)) Range extends from southwestern British Columbia (Dunbar et al. 1991) southward through the Coast Ranges and Cascade Range (both west and east sides) of Washington and Oregon to northwestern California north of San Francisco (Marin County) and northwest of the Pit River in northeastern Shasta County (the Pit River boundary between subspecies caurina and occidentalis is based on biogeographic considerations, rather than on adequate taxonomic data from that area) (Thomas et al. 1990). The population on the Olympic Peninsula appears to be reproductively isolated (by nonforested lands of the Puget Trough) from owls in the Cascade Range. The Columbia River may constitute an isolating barrier between the Cascades populations in Washington and Oregon. Population size and density are relatively low at the northern and southern ends of the range.

Historic Range:
U.S.A. (CA, OR, WA), Canada (B.C.)

medium-sized, brown owl. round or oval irregular white spots on head, neck, back, and underparts. no ear tufts. flight feathers dark brown barred with light brown or white. female larger than male.

Length: 45 cm

Differs from other subspecies in being darker, with lighter markings more reduced in size, and with the legs and feet more heavily mottled (Ridgway 1914).

Northern Spotted Owls inhabit old growth forests and younger forests with remnants of larger trees. They prefer these forests because they provide a canopy forprotection from predators and the elements, large open spaces for flight, wood debris for nests, and old hollow trees for nesting sites.

Terrestrial Biomes: forest

Comments: Thomas et al. (1990) found that typical habitat characteristics include: "moderate to high canopy closure; a multilayered, multispecies canopy dominated by large overstory trees; a high incidence of large trees with large cavities, broken tops, and other indications of decadence; numerous large snags; heavy accumulations of logs and other woody debris on the forest floor; and considerable open space within and beneath the canopy." Generally these conditions are found in old growth (at least 150-200 years old), but sometimes they occur in younger forests that include patches of older growth; in Washington and Oregon, conifer forests begin to develop conditions suitable for spotted owls about 80-120 years after clearcutting; coastal redwood forests are exceptional in that stands that are 50-80 years old or so may provide suitable conditions. Can tolerate some degree of habitat fragmentation (e.g., as on BLM lands in western Oregon) (Thomas et al. 1990). In southwestern Oregon, almost all owls consistently selected old forest for foraging and roosting (Carey et al. 1992). In northwestern California, nest and roost sites had more old-growth and mature forest and were less fragmented than were random sites (Hunter et al. 1995).

Recent landscape-level analyses in portions of the California Klamath and Oregon Coast Province suggest that a mosaic of mid-seral and late-successional nesting habitat interspersed with other seral conditions may result in high fitness for spotted owls (see USFWS 2007), but other studies have not found that correlation (e.g., Dugger et al. 2005).

Nests on broken tree top, cliff ledge, in natural tree cavity, or in tree on stick platform, often the abandoned nest of hawk or mammal; sometimes in cave. In western Oregon, the proportion of old-growth and mature forest was significantly greater at nest sites than at random sites (Ripple et al. 1991). Pairs tend to occupy the same nesting territories in successive years, as long as habitat remains suitable (Thomas et al. 1990).

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Some individuals migrate locally between nonoverlapping summer and winter home ranges (Thomas et al. 1990).

Juveniles disperse usually less than 100 km but sometimes up to more than 150 km. In Oregon and Washington, Forsman et al. (2002) found that final dispersal distances of juvenile northern spotted owls ranged from 0.6-111.2 km for banded juveniles and 1.8-103.5 km for radio-marked juveniles; only 8.7% of individuals dispersed more than 50 km. Median natal dispersal distances were 14.6 km for banded males, 13.5 km for radio-marked males, 24.5 km for banded females, and 22.9 km for radio-marked females. Final dispersal distance was based on the distance between the natal site and the sites in which owls settled on a territory (generally when they were 2-5 years old).

In western Oregon and northwestern California, juveniles dispersed an average of about 20 miles (32 km); two-thirds dispersed more than 12 miles (Thomas et al. 1990). In Oregon and Washington, 22-45% of juveniles that survived the first year of life emigrated from their natal areas (Thomas et al. 1993). Dispersing juveniles owls experience high mortality (see USFWS 2007).

USFWS uses a circle of 0.7-mile radius (984 acres) from the activity center to delineate the most heavily used area during the nesting season. Spotted owls use smaller home ranges during the breeding season and often dramatically increase their home range size during fall and winter (see USFWS 2007).

Median annual home range for pairs in 13 of 14 areas in California, Oregon, and Washington varied from 1411 to 6390 acres (range 1035-10,189 acres); on the Olympic Peninsula, home ranges were substantially larger, with a median of 9930 acres (range 4497-27,309 acres) (see Thomas et al. 1990). Habitat fragmentation tends to result in an increase in home range size for individual owls. Carey et al. (1992) found that owl pairs in southwestern Oregon annually used areas averaging about 530-1800 sq km in old mixed-conifer forest, and about 1570-2900 sq km in old Douglas-fir forest; ranges were largest in fragmented forests; overlap among pairs and separation of birds within pairs increased with fragmentation.

Northern Spotted Owls are nocturnal birds that feed primarily on small mammals, but also take birds, reptiles and insects. Northern flying squirrels are their main prey, but they also consume significant numbers of red tree voles, deer mice, and woodrats.

Comments: Small mammals, particularly nocturnal arboreal or semi-arboreal species, dominate the diet; flying squirrels, woodrats, and lagomorphs are common prey items, with pocket gophers, red tree voles, and deer mice are regionally important; flying squirrels are comsumed more often at higher latitudes and higher elevations, woodrats more often at lower latitudes and lower elevations (Thomas et al. 1990).

Generally, flying squirrels are the most prominent prey for spotted owls in Douglas-fir and western hemlock forests in Washington and Oregon, while dusky-footed wood rats are a major part of the diet in the Oregon Klamath, California Klamath, and California Coastal provinces (see USFWS 2007 for specific sources of this information).

Olympic Peninsula, Washington: primary prey included flying squirrels, woodrats, and snoeshoe hares (Carey et al. 1992). Oregon: diet dominated by flying squirrels and red tree voles in Douglas-fir and western hemlock forest; woodrats in mixed coniferous forest; pocker gophers and voles (Clethrionomys) at higher elevations. California: mostly flying squirrels, woodrats, and gray squirrels.

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 81 - 300

Comments: This subspecies is represented by a large number of occurrences (subpopulations).

2500 - 100,000 individuals

Comments: In the late 1980s, some 2000 pairs were located or reconfirmed from earlier surveys; this number is an unknown fraction of the total population, which is suspected to be between 3000 and 4000 pairs (Thomas et al. 1990). In the late 1980s and early 1990s a total of 3605 pairs were located rangewide (incomplete survey); 954 pairs in California, 1977 in Oregon, 660 in Washington, and 14 in Canada (Thomas et al. 1993).

Dunbar et al. (1991) estimated the British Columbia population at not more than 100 pairs; remaining habitat 7.1 million acres. Blackburn et al. (2002) estimated that fewer than 50 breeding pairs occur within British Columbia. More recently, British Columbia breeding populations have been estimated at fewer than 33 pairs (Chutter et al. 2004).

As of July 1, 1994, there were 5,431 known site centers of northern spotted owl pairs or resident singles: 851 sites (16 percent) in Washington, 2,893 sites (53 percent) in Oregon, and 1,687 sites (31 percent) in California (see USFWS 2007). The number of currently occupied spotted owl locations across the range is unknown because many areas remain unsurveyed (USFWS 2007).

In southwestern Oregon, density ranged from 0.190 pairs/sq km in old unfragmented mixed-conifer forest to 0.046 pairs/sq km in old fragmented Douglas-fir forest (Carey et al. 1992).

Population density estimates range from 0.09/sq km in Washington to 0.36/sq km in Oregon (Johnsgard 1988); 0.24/sq km in northwestern California (about 0.6/sq km of suitable habitat) (Franklin et al. 1990). Density estimates for 12 study areas during 1985-1992 ranged up to 0.27 adults and subadults/sq km (Thomas et al. 1993).

Comments: Roosts during the day; hunts at dusk and at night. May leave roost during day to capture prey near roost (e.g., see Sovern et al. 1994), retrieve cached prey, or to drink or bathe in stream.

Northern Spotted Owls mate in pairs, usually for life. They nest in hollow trees or crevices in cliffs; spots that are well hidden and that provide protection from extreme temperatures. They sometimes use squirrel or raptor nests as platforms on which to build their own nests. Pairs form in February or March and egg laying takes place in March and April. They most commonly lay two to three white eggs. One brood is produced each season. Eggs are incubated for 30 days, and the young fledge 34-36 days after hatching. The female incubates the egg and broods the young for the first 8-10 days after hatching; during this period, the male brings her food. Some owls forage during the day to take care of the young at night.

The spotted owl is relatively long-lived, has a long reproductive life span, invests significantly in parental care, and exhibits high adult survivorship relative to other North American owls (USFWS 2007).

USFWS (2007) summarized life history as follows. Courtship behavior usually begins in February or March, and females typically lay eggs in late March or April. The timing of nesting and fledging varies with latitude and elevation. Breeding females lay 1-4 four eggs per clutch, with the average clutch size being two eggs; however, most pairs do not nest every year, nor are nesting pairs successful every year. Renesting (in different nest) after nest failure is infrequent. Incubation, by the female (fed by male), lasts about 30 days. Young leave the nest at about 5 weeks, fly at about 6 weeks. After they leave the nest in late May or June, juveniles depend on their parents until they are able to fly and hunt on their own. Parental care continues after fledging into September. During the first few weeks after the young leave the nest, the adults often roost with them during the day. By late summer, the adults are rarely found roosting with their young and usually only visit the juveniles to feed them at night. Spotted owls are sexually mature at 1 year of age, but rarely breed until they are 2 to 5 years of age. See USFWS (2007) for specific sources of this information.

Current Listing Status Summary

Status: Threatened
Date Listed: 06/26/1990
Lead Region:   Pacific Region (Region 1) 
Where Listed: Entire

Population detail:

Population location: Entire
Listing status: T

For most current information and documents related to the conservation status and management of Strix occidentalis caurina , see its USFWS Species Profile

Harvesting of old growth forests affects the owls by decreasing the area of appropriate habitat. Somewhere between 54% and 99% of appropriate habitat has been lost. Forests can be reinhabited 40-100 years after logging if snags, coarse debris, and some trees with cavities are left by loggers. Recently, the survival rate of the juveniles has also been a problem. Protecting old growth forests would protect these owls, but the human costs are high. Northern Spotted Owls have been studied extensively, and they are the subject of much current debate and litigation.

Canada

Rounded National Status Rank: N1 - Critically Imperiled

United States

Rounded National Status Rank: N3 - Vulnerable

Rounded Global Status Rank: T3 - Vulnerable

Reasons: Fairly large range (British Columbia to northern California) but relatively few occurrences are of high quality, and population trend is downward, so this owl remains of significant conservation concern; decline is due to past and continuing loss and/or fragmentation of habitat resulting from timber harvest, effects of barred owls, and other factors.

Intrinsic Vulnerability: Moderately vulnerable

Comments: Small clutch size, temporal variability in nesting success, and delayed onset of breeding all contribute to the relatively low fecundity of this species (Gutiérrez 1996).

Other Considerations: This is a high profile subspecies to which apply a large number of policies and regulations.

Global Short Term Trend: Decline of 10-30%

Comments: Many populations are declining, especially in the northern parts of the range (USFWS 2007). Recent demographic data suggest that populations in 13 long-term demographic study areas decreased by about 3.7 percent per year from 1985 to 2003 (Anthony et al. 2006, USFWS 2007).

Range-wide monitoring of northern spotted owl populations and habitat during the first 10 years of implementation of the Northwest Forest Plan (1994-2003) yielded estimated annual population declines of 0 to 10 percent across study areas (weighted average = 3.4 percent); the average annual rate of decline for the four demographic areas in Washington was 7.1 percent (Anthony et al. 2004, Lint 2005).

In British Columbia, Blackburn et al. (2002) monitored the occupancy of spotted owls within 40 survey areas between 1992 and 2001. Spotted owl occupancy declined by 49% between 1992 and 2001. The average annual rate of decline was -7.2%. The substantial decline between 1992 and 2001 occurred despite protection of suitable habitat during a large portion of the 10-year study within 39 of the 40 survey areas and Special Resource Management Zones (SRMZs). Results suggested that the decline may have slowed in recent years, possibly in response to habitat protection measures. Assuming that the study area is representative of the entire spotted owl population in B.C., then the number of spotted owls in B.C. is not stable, but has declined sharply over the past 10 years. Blackburn et al. (2002) concluded that current suitable habitat levels protected in SRMZs under the Spotted Owl Management Plan are inadequate to stabilize the owl population; the population is expected to decline further over the next few decades. Accordingly, Chuttrer et al. (2004) estimated that breeding populations in British Columbia may be declining by as much as 35 percent per year (Chutter et al. 2004), and more recent studies indicate that the decline is continuing (USFWS 2007). The amount of interaction between spotted owls in Canada and the United States is unknown (Chutter et al. 2004).

Global Long Term Trend: Decline of 30-70%

Comments: Area of occupancy, number of subpopulations, and population size have undergone a significant long-term decline, but the precise level of decline is uncertain.

As of 1990, habitat reduction was continuing at a rangewide rate of 1-2% per year, and the owl was threatened by extirpation in significant portions of its range (Thomas et al. 1990). Thomas et al. (1993) concluded that habitat loss was occurring at a rate of about 1-5% per year. Territorial female population declined by an estimated average of 7.5% each year during 1985-1991 (Thomas et al. 1993). Overall population on 12 study areas declined at a rate of 3.2% per year during 1985-1992 (Thomas et al. 1993). Populations in the Klamath Mountains of California and in the Coast Range of Oregon were declining in the late 1980s (Thomas et al. 1990). In northwestern California, a 60-83% reduction in population was recorded on at least one National Forest under current management plans by the U.S. Forest Service (Franklin et al. 1990). USFWS (1990) categorized the status as "declining." Though one demographic analysis concluded that the northern spotted owl population was stable, Taylor and Gerrodette (1993) showed that this conclusion was not statistically justified.

An analysis of all capture-recapture data showed a declining annual survival rate for adults on 11 large study areas during 1985-1993 (Burnham et al. 1996). Burnham et al. (1996) concluded that there was a plausible inference of a declining population during the study period and that the rate of population decline was accelerating.

In a range-wide analysis based on estimates of demographic parameters averaged across multiple studies and juvenile survival corrected for emigration, Franklin et al. (1999) estimated that the population of territorial females declined at a annual rate of 3.9% udring the 1980s and 1990s. Although the overall analysis indicated a declining population, some individual study areas appeared to have stationary (i.e., stable) populations whereas other studies suggested substantial declines. Another model that only capture-recapture data from selected studies suggested that most of the selected study areas had stationary populations. However, three study areas exhibited evidence indicating that populations were declining on these areas. The authors concluded that "there is still uncertainty regarding the health of the spotted owl population."

In northwestern California, among basic demographic parameters, annual survival varied the least over time whereas recruitment rate varied the most (Franklin et al. 2000). A forecast of annual rates of population change, estimated from life history traits, suggested that populations may change solely due to climate influences (e.g., annual variations in temperature and precipitation), even with unchanging habitat conditions (Franklin et al. 2000).

Degree of Threat: High

Comments: In a major range-wide analysis, Lint et al. (2005) concluded that presence of barred owls (Strix varia), weather, past and present harvest of habitat, and wildfire and insect infestations that alter habitat are all possible contributors to declines in northern spotted owl populations. Lint et al. (2005) determined that barred owls, West Nile virus (Flavivirus sp.), and management of owl habitat in high-fire-risk areas are topics for future management consideration.

Habitat continues to be lost or degraded by logging and/or forest fragmentation, but the rate of loss has slowed. A perhaps conservative estimate is that habitat has been reduced by about 60% since 1800; habitat loss (including that due to fragmentation) has been due primarily to logging, but natural disturbances also have played a role (Thomas et al. 1990).

Spotted owls may be threatened by the recent expansion of the range of the barred owl into the Pacific Northwest; barred owls possibly could compete with or displace spotted owls. For example, Kelly et al. (2003) found that occupancy of spotted owl territories in Oregon and Washington declined after barred owls were detected within 0.80 kilometers of the territory center. Between 1974 and 1998, the authors estimated that 706 different barred owl territories were located in Oregon. From 1989-1998, an average of 60 new barred owl territories were located in Oregon each year. USFWS (2007) concluded that the most important threat currently facing the spotted owl is competition from the barred owl. Hybridization between spotted owls and barred owls has been detected but is relatively rare (Thomas et al. 1993, Hamer et al. 1994, Seamans et al. 2004) and has been recorded most often in Oregon.

Based on data from all three spotted owl subspecies, Bond et al. (2002) hypothesized that "wildfires may have little short-term impact on survival, site fidelity, mate fidelity, and reproductive success of spotted owls. Further, prescribed burning could be an effective tool in restoring habitat to natural conditions with minimal short-term impact on resident spotted owls."

Management Requirements: In 2007, USFWS released a draft recovery plan for the northern spotted owl that identifies criteria and actions needed to stop the owl's decline, reduce threats and return the species to a stable, well-distributed population in Washington, Oregon and California (USFWS 2007).

Thomas et al. (1990) described a conservation strategy, basic elements of which are habitat conservation areas that contain a minimum of 20 pairs of owls. The late 1980s management strategy for Forest Service and BLM lands, which entailed protecting enough suitable habitat to support units of one to three pairs of owls, was found by Thomas et al. (1990) to be inadequate, poorly coordinated, and otherwise unacceptable as a means of preventing the extirpation of the owl from significant portions of its range. See 1990 Endangered Species Tech. Bull. 15(7) for a brief description of an alternative approach to owl management, proposed by the secretaries of the Interior and Agriculture in response to the plan described by Thomas et al. (1990).

According to mathematical demographic analysis by Noon and Biles (1990), sound management practices should include efforts to control factors that adversely affect survival of adult females. See Dawson et al. (1987) and Lefranc and Glinski (1988) for additional management and research recommendations. See also U.S. Forest Service et al. (1993) for a discussion of management issues. In mid-1993, U.S. Forest Service and BLM (Federal Register, 9 June 1993) published a notification of intent to prepare a Supplemental Environmental Impact Statement for management standards and guidelines for the conservation and management of habitat for the northern spotted owl and old-growth-related species.

See Thomas et al. (1993) for viability assessments and management considerations for species associated with late-successional and old-growth forests of the Pacific Northwest. See Lamberson et al. (1992) for a study of viability in a fragmented forest landscape. See Boyce and Irwin (1990) for a review of the U.S. Forest Service's spotted owl viability analysis (viewed as unrealistic).

See USFWS (1993) for information pertaining to a petition to allow incidental take related to timber harvest in eastern Lewis County, Washington.

"Silvicultural manipulation of vegetation and creative snag or den-tree management could be used...to accelerate the development of spotted owl habitat in areas where old growth is lacking" (Carey 1995).

Management Research Needs: Determine population attributes and trends in relation to existing management activities. Determine silvicultural techniques that could produce wood products and owls. Determine ways to make younger forests capable of supporting owls.

Global Protection: Many to very many (13 to >40) occurrences appropriately protected and managed

Comments: Many occurrences are in national parks and other protected areas, but this does not necessarily ensure the absence of significant threats in those areas.

On January 15, 1992, USFWS designated critical habitat for the spotted owl within 190 Critical Habitat Units (CHUs), which encompass a total of nearly 6.9 million acres. CHUs total 2.2 million acres in Washington, 3.3 million acres in Oregon, and 1.4 million acres in California. USFWS is in the process of revising critical habitat (USFWS 2007).

See USFWS (2007) for further information on conservation efforts and regulations.

Needs: Protect large tracts of old growth forest or younger forest of similar vegetative structure (e.g., redwood forest). See draft recovery plan (USFWS 2007).

Since the owls became threatened in 1990, logging in old growth forests has been restricted, resulting in job loss and economic disruption in the Pacific northwest. This has become a very important political and economic issue.

These birds play an important role in the food chain of old growth forests. The owls depend on a healthy diverse ecosystem for survival. They help keep the populations of their prey under control. They are also an attraction to birdwatchers, who bring in tourist dollars.

Comments: Certain special interest groups oppose the protection of owl habitat because they view it as economically unfavorable.