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Wildlife, Animals, and Plants
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Introductory
WILDLIFE SPECIES: Strix occidentalis | Spotted Owl
ABBREVIATION :
STOC
COMMON NAMES :
spotted owl
northern spotted owl
California spotted owl
Mexican spotted owl
southern spotted owl
TAXONOMY :
The currently accepted scientific name for the spotted owl is Strix
occidentalis (Xantus). The American Ornithologist Union recognizes three
subspecies of spotted owl [5,17,22]:
Strix occidentalis occidentalis - California spotted owl
Strix occidentalis caurina (Merriam) - northern spotted owl
Strix occidentalis lucida (Nelson) - Mexican spotted owl
Some doubt the validity of the separation of the northern and California
subspecies [5,17]. Recent studies of genetic differences among spotted
owls over much of their range in the western United States showed
essentially no genetic difference between the northern and California
subspecies. However, several morphological features that exhibit clinal
variation from north to south across the range of the northern and
California subspecies have been identified [17].
ORDER :
Strigiformes
CLASS :
Bird
FEDERAL LEGAL STATUS :
See OTHER STATUS
OTHER STATUS :
The northern and Mexican spotted owls are federally listed as threatened
[23]. The California spotted owl is listed as a Category 2 subspecies [24].
Spotted owls are state listed as endangered in Washington [25].
In British Columbia, the northern spotted owl is listed as endangered
[26].
COMPILED BY AND DATE :
Julie L. Tesky, October 1992
LAST REVISED BY AND DATE :
AUTHORSHIP AND CITATION :
Tesky, Julie L. 1992. Strix occidentalis. In: Remainder of Citation
WILDLIFE DISTRIBUTION AND OCCURRENCE
WILDLIFE SPECIES: Strix occidentalis | Spotted Owl
GENERAL DISTRIBUTION :
The general distribution of the three spotted owl subspecies is as
follows:
California spotted owl - northeastern Tehama County, California, south
through the Sierra Nevada and the high mountain ranges of southern
California, and in the Coast Ranges from southern California north to
Monterey County [5,11].
Northern spotted owl - southwestern British Columbia south through the
Coast Ranges and Cascade Range (both west and east sides) of Washington
and Oregon, south into southwestern Oregon and northwestern California
north of San Francisco [5,9,17].
Mexican spotted owl - southern Utah and central Colorado, south through
the mountainous regions of Arizona and New Mexico; Guadalupe Mountains
of western Texas; mountains of northern and central Mexico south to
Michoacan and Guanajuato [5].
ECOSYSTEMS :
FRES20 Douglas-fir
FRES21 Ponderosa pine
FRES22 Western white pine
FRES23 Fir-spruce
FRES24 Hemlock-Sitka spruce
FRES25 Larch
FRES26 Lodgepole pine
FRES27 Redwood
FRES28 Western hardwoods
FRES35 Pinyon-juniper
STATES :
BLM PHYSIOGRAPHIC REGIONS :
1 Northern Pacific Border
2 Cascade Mountains
3 Southern Pacific Border
4 Sierra Mountains
7 Lower Basin and Range
11 Southern Rocky Mountains
12 Colorado Plateau
13 Rocky Mountain Piedmont
KUCHLER PLANT ASSOCIATIONS :
K001 Spruce - cedar - hemlock forest
K002 Cedar - hemlock - Douglas-fir forest
K003 Silver fir - Douglas-fir forest
K003 Silver fir - Douglas-fir forest
K005 Mixed conifer forest
K006 Redwood forest
K007 Red fir forest
K009 Pine - cypress forest
K018 Pine - Douglas-fir forest
K019 Arizona pine forest
K020 Spruce - fir - Douglas-fir forest
K021 Southwestern spruce - fir forest
K023 Juniper - pinyon woodland
K025 Alder - ash forest
K026 Oregon oakwoods
K029 California mixed evergreen forest
K030 California oakwoods
K031 Oak - juniper woodlands
SAF COVER TYPES :
210 Interior Douglas-fir
211 White fir
212 Western larch
213 Grand fir
215 Western white pine
216 Blue spruce
217 Aspen
218 Lodgepole pine
221 Red alder
222 Black cottonwood - willow
223 Sitka spruce
224 Western hemlock
225 Western hemlock - Sitka spruce
226 Coastal true fir - hemlock
227 Western redcedar - western hemlock
228 Western redcedar
229 Pacific Douglas-fir
230 Douglas-fir - western hemlock
231 Port-Orford-cedar
232 Redwood
233 Oregon white oak
234 Douglas-fir - tanoak - Pacific madrone
237 Interior ponderosa pine
239 Pinyon - juniper
240 Arizona cypress
241 Western live oak
243 Sierra Nevada mixed conifer
244 Pacific ponderosa pine - Douglas-fir
245 Pacific ponderosa pine
246 California black oak
247 Jeffrey pine
249 Canyon live oak
250 Blue oak - Digger pine
255 California coast live oak
SRM (RANGELAND) COVER TYPES :
NO-ENTRY
PLANT COMMUNITIES :
Spotted owls occupy a variety of forest types, from humid coniferous
forests in the northern part of its range to xeric pine (Pinus spp.)-oak
(Quercus spp.) woodlands in the mountains and canyonlands of Mexico and
the American Southwest [9].
In California, northern spotted owls most commonly use Douglas-fir
(Pseudotsuga menziesii) and mixed-conifer forest types but have also
been found in redwood (Sequoia sempervirens) forests, Bishop pine (Pinus
muricata) forests, and in stands dominated by ponderosa pine (P.
ponderosa). In Washington's coastal forests, the northern spotted owl
is found in forests dominated by Douglas-fir and western hemlock (Tsuga
heterophylla). At higher elevations in western Washington, Pacific
silver fir (Abies amabilis) is commonly used, whereas on the east side
of the Cascades, Douglas-fir and grand fir (A. grandis) are used
[17,19]. Forsman [9] found that spotted owls in Oregon used all mature
coninferous forests except subalpine fir (A. lasiocarpa) and nearly
monospecific forests of ponderosa pine and lodgepole pine (Pinus
contorta) or Sitka spruce (Picea sitchensis). Some hardwood stands are
also used [11]. Understory layers are often dominated by shade-tolerant
trees such as western hemlock, western redcedar (Thuja plicata),
Port-Orford-cedar (Chamaecyparis lawsoniana), grand fir, white fir
(Abies concolor), Shasta red fir (A. magnifica shastensis), Pacific yew
(Taxus brevifolia), vine maple (Acer circinatum), canyon live oak
(Quercus chrysolepis), California bay (Umbellularia callfornica), and
tanoak (Lithocarpus densiflora) [9].
California spotted owls typically occupy Douglas-fir or fir-pine forests
and oak woodlands [12,20]. California spotted owls have been found
nesting in stands composed of mixtures of interior live oak (Quercus
wislizenii), California sycamore (Platanus racemosa), California buckeye
(Aesculus californica), and blue oak (Quercus douglasii) [17]. Mexican
spotted owls occupy spruce, Douglas-fir and pinyon (Pinus spp.)-juniper
(Juniperus spp.) forests. Aspen (Populus spp.) and maple (Acer spp.)
stands are also used [12]. Major plant species in canyons occupied by
Mexican spotted owls typically include ponderosa pine, firs, and
deciduous trees such as oaks and boxelder (Acer negundo) [5].
REFERENCES :
NO-ENTRY
BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Strix occidentalis | Spotted Owl
TIMING OF MAJOR LIFE HISTORY EVENTS :
Breeding - Spotted owls can breed as early as 1 year of age; however,
most birds do not breed before they are 3 years old [9,15].
Courtship - Spotted owl pairs begin to roost together in February or
March. Some owls use the same nest site repeatedly, some
use new ones, and others alternate nest sites from year to
year. Although a pair may occupy and defend a territory,
they may not nest every year [15].
Clutch - In March or April, spotted owls lay one to three eggs, usually
two. The female incubates the eggs for approximately 30 days
and broods the young. The male provides most of the food for
the young [15].
Fledging - Spotted owls fledge in May or June (3 to 5 weeks after
hatching). The young are fed by both parents until August or
September [9,15,17].
Dispersal - By October the young become independent and disperse from
the parental nest area. Dispersing young do not typically
acquire territories until they are 2 to 3 years old [15].
Lifespan - The average life span of the spotted owl is 15 to 20 years [15].
PREFERRED HABITAT :
Nesting habitat: Spotted owls do not build nests but use naturally
occurring sites. They generally nest in cool, shaded areas with
well-developed understory. They prefer natural cavities in
large-diameter trees with broken tops and mistletoe infestations.
Spotted owls will also nest in cliff cavities and abandoned hawk or
raven (Corvus corax) nests [6,9,17].
Northern spotted owl - Components of northern spotted owls preferred
habitat are as follows: moderate to high canopy closure (60 to 80
percent); a multilayered, multispecies canopy dominated by large (> 30
inches d.b.h. [76 cm]) overstory trees; a high incidence of large trees
with various deformities; numerous large snags; large accumulations of
fallen trees and other woody debris on the ground; and sufficient open
space below the canopy for owls to fly [17,19].
Northern spotted owls have been observed over a wide range of
elevations, although they avoid higher elevation, subalpine forests
[12,19]. A strong selection of old growth for roosting, foraging and
nesting is a consistent finding in studies of spotted owl habitat
[4,8,9,15,17]. Breeding and roosting habitat are sometimes found in
younger forests, especially those with significant remnants of earlier
stands that were influenced by fire, wind storms, or inefficient logging
operations. However, nearly all nest and major roost sites are located
in older components of these stands [17]. Forsman [9] found that 98.3
percent of the sites where northern spotted owls were located were
forested with old-growth (> 200 years old) conifers or mixtures of
mature (100-200 year old) and old-growth conifers. A little over 1
percent of the pairs occupied second growth conifer forest in which
small patches of old growth were present, and 0.5 percent occupied
second growth forests with little or no old growth present. No owls
were located in forests younger than 36 years.
The median home range size for northern spotted owl pairs is 3,000 to
5,000 acres (1,214-2,023 ha). Reduction in the proportional coverage of
suitable foraging habitat causes spotted owls to increase the size of
their home ranges to encompass additional foraging habitat [9,17]. In
Oregon, areas with median pair ranges greater than 5,000 acres (2,023
ha) were typically in heavily logged areas where the proportion of the
landbase covered by older forests was low [17].
California spotted owl - Habitat requirements of the California spotted
owl are similar to those of the northern spotted owl [3,5]. However,
California spotted owls will use mid-successional forests to some degree
for foraging [3]. In foothill woodlands of western Sierra Nevada, east
of Fresno, several pairs of California spotted owls have been found
nesting in or near riparian habitats in canyons at elevations ranging
from about 1,000 to 3,000 feet (305-914 m) [17]. During the winter
California spotted owls occupied pine-oak woodlands. Mixed-conifer
forest were used during the summer. All wintering areas were below the
levels of persistent winter snow [11].
Mexican spotted owl - In the Southwest, spotted owls are commonly found
in forested mountain tablelands and canyons from 5,500 to 9,000 feet
(1,676-2,743 m) [6]. In the mountains of New Mexico, spotted owls favor
deep, narrow timbered canyons where there are always cool shady places.
Six spotted owls located in Zion National Park, Utah, were in very
narrow, steep-walled canyons at an elevation of 5,118 feet (1,560 m).
Mexican spotted owls are assumed to migrate to lower elvations for the
winter [5].
COVER REQUIREMENTS :
Spotted owls require stands with high canopy closure for thermal
regulation and hiding cover [1,11,17]. They are intolerant of high
temperatures and are stressed at temperatures above 80 to 87 degrees
Fahrenheit (27-31 deg C) [11]. Spotted owls tend to roost in small
trees in the forest understory during warm weather and high up in the
large trees during cold or wet weather. The layered canopy structure in
old forests provide both types of roosts [17].
FOOD HABITS :
Spotted owl prey mainly on small mammals, particularily arboreal or
semiarboreal species, although birds, insects, and other types of small
mammals are taken as well [17]. Prey species composition varies with
cover type. In Oregon, northern flying squirrels (Glaucomys sabrinus)
and red tree voles (Arborimys longicaudus) are the dominant species in
forests of Douglas-fir and western hemlock, while dusky-footed woodrats
(Neotoma fuscipes) predominated in the diets of owls living in mixed
conifer forests. There appears to be a greater frequency of northern
flying squirrels in the diets of owls in moist habitats, with wood rats
(Neotama spp.) predominating as food in drier habitats. At higher
elevations in Oregon, pocket gophers (Thomomys spp.) and red-backed
voles (Clethrionomys spp.) are the major prey items [5]. Analysis of
the contents of 800 pellets from California spotted owls showed
approximately equal proportions of northern flying squirrels,
dusky-footed woodrats, and western gray squirrels (Sciurus griseus)
[15]. Remains of woodrats, pocket gophers, and beetles were found in
pellets of spotted owls in Zion National Park [5]. One study showed
that insects as prey were important only during late summer and early
fall. Two insects that were common in summer diets were a large flying
beetle (Ergates spiculatus) and a large arboreal cricket (Cyphoderris
monstrosa) [9].
PREDATORS :
Common predators of the spotted owl include the great horned owl (Bubo
virginianus), northern goshawk (Accipiter gentilis), Cooper's hawk
(Accipiter cooperii), and red-tailed hawk (Buteo jamaicensis). The
common raven is also considered a predator, more likely preying on
juvenile spotted owls rather than adult owls [15,17]. In some areas
great horned owl predation is a major cause of juvenile mortality [9].
MANAGEMENT CONSIDERATIONS :
As the northern spotted owl's habitat has declined, the population of
owls has also decreased. Logging and other forest management practices
in the Pacific Northwest have resulted in fragmented patches of older
forests separated by young forests that have yet to develop into
suitable spotted owl habitat. To provide for conservation of the
northern spotted owl, adequate distribution of appropriate forest
structure is necessary so that as older forest stands are lost they are
replaced by mature stands within a relatively short period of time.
This distribution would allow for the perpetuation of high quality owl
habitat for nesting, roosting, and foraging [19].
Silvicultural practices that produce multilayered stands and leave
structures such as large trees, snags, and downed woody debris could
retain suitable habitat for spotted owls. Some evidence suggests that
historical methods of logging, which left numerous remnant trees or
patches of trees and large amounts of woody debris, could produce
suitable habitat in a much shorter period that can methods such as
clearcutting and burning [17].
Competition with barred owls (Strix varia) may be displacing spotted
owls in some areas. Relative density of barred owls is high in many
areas of the spotted owl's range. Further habitat fragmentation may
increase displacement [17]. Hybridization between the two species has
also been documented [15].
REFERENCES :
NO-ENTRY
FIRE EFFECTS AND USE
WILDLIFE SPECIES: Strix occidentalis | Spotted Owl
DIRECT FIRE EFFECTS ON ANIMALS :
No specific information regarding the direct fire effect on spotted owls
was found. However, direct fire related mortality on spotted owls
probably occurs. Fire may also destroy nests.
HABITAT RELATED FIRE EFFECTS :
Most spotted owl habitat owes its structure and species composition to
fire [15]. Historically, spotted owls occupied a dynamic landscape that
often consisted of large areas of burned and unburned forest. Today,
however, habitat is greatly reduced and fragmented, and owl populations
have become increasingly vulnerable to loss of habitat due to fire
[15,17]. Fires can cause further habitat fragmentation and loss of
preferred suitable old growth. One study showed that areas that had
been clearcut or burned within the previous 20 years were rarely used by
spotted owls for foraging. Additionally, spotted owls usually avoided
crossing burned areas by traveling through corridors of unburned timber
around the area [17].
FIRE USE :
NO-ENTRY
REFERENCES :
NO-ENTRY
References for species: Strix occidentalis
1. Barrows, Cameron. 1980. Feeding ecology of the spotted owl in California. Raptor Research. 14(3): 73-78. [25175]
2. Bernard, Stephen R.; Brown, Kenneth F. 1977. Distribution of mammals, reptiles, and amphibians by BLM physiographic regions and A.W. Kuchler's associations for the eleven western states. Tech. Note 301. Denver, CO: U.S. Department of the Interior, Bureau of Land Management. 169 p. [434]
3. Bias, Michael A.; Gutierrez, R. J. 1992. Habitat associations of California spotted owls in the central Sierra Nevada. Journal of Wildlife Management. 56(3): 584-595. [19279]
4. Carey, Andrew B.; Reid, Janice A.; Horton, Scott P. 1990. Spotted owl home range and habitat use in southern Oregon Coast Ranges. Journal of Wildlife Management. 54(1): 11-17. [15059]
5. Dawson, W. R.; Ligon, J. D.; Murphy, J. R.; [and others]. 1989. Report of the Scientific Advisory Panel for the northern spotted owl. The Condor. 89: 205-229. [18981]
6. DeGraaf, Richard M.; Scott, Virgil E.; Hamre, R. H.; [and others]. 1991. Forest and rangeland birds of the United States: Natural history and habitat use. Agric. Handb. 688. Washington, DC: U.S. Department of Agriculture, Forest Service. 625 p. [15856]
7. Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Washington, DC: Society of American Foresters. 148 p. [905]
8. Forsman, Eric D.; Meslow, E. Charles, Strub, M. J. 1976. Spotted owl abundance in second-growth versus old-growth forest. Bulletin of the Wildlife Society of Washington. 5(2): 43-47. [18982]
9. Forsman, Eric D.; Meslow, E. Charles; Wight, Howard M. 1984. Distribution and biology of the spotted owl in Oregon. Wildlife Monographs. 87: 0084-0173. [18983]
10. Garrison, George A.; Bjugstad, Ardell J.; Duncan, Don A.; [and others]. 1977. Vegetation and environmental features of forest and range ecosystems. Agric. Handb. 475. Washington, DC: U.S. Department of Agriculture, Forest Service. 68 p. [998]
11. Gutierrez, Ralph J.; Carey, Andrew B, eds. 1985. Ecology and management of the spotted owl in the Pacific Northwest; 1984 June 19 - June 23; Arcata, CA. Gen. Tech. Rep. PNW-185. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station: 119 p. [18115]
12. Kochert, Michael N. 1986. Raptors. In: Cooperrider, Allan Y.; Boyd, Raymond J.; Stuart, Hanson R., eds. Inventory and monitoring of wildlife habitat. Denver, CO: U.S. Department of the Interior, Bureau of Land Management, Denver Service Center: 313-349. [13527]
13. Kuchler, A. W. 1964. Manual to accompany the map of potential vegetation of the conterminous United States. Special Publication No. 36. New York: American Geographical Society. 77 p. [1384]
14. Laymon, Stephen A.; Salwasser, Hal; Barrett, Reginald H. 1985. Habitat suitability index model: spotted owl. Washington, DC: U.S. Department of the Interior, Fish and Wildlife Service. 14 p. [18984]
15. Lujan, Manuel, Jr.; Knowles, Donald R.; Turner, John; [and others]. 1992. Draft recovery plan for the northern spotted owl. keyw SPOTTED OWL, NORTHERN SPOTTED OWL, MGMT, [18985]
16. Ripple, William J.; Johnson, David H.; Hershey, K. T.; Meslow, E. Charles. 1991. Old-growth and mature forests near spotted owl nests in western Oregon. Journal of Wildlife Management. 55(2): 316-318. [15164]
17. Thomas, Jack Ward; Forsman, Eric D.; Lint, Joseph B.; [and others]. 1990. A conservation strategy for the northern spotted owl. Report ot the Interagency Scientific Committee to address the conservation of the northern spotted owl. [18986]
18. U.S. Department of Agriculture. 1977. Cavity-nesting birds of North American forests. Agric. Handb. 511. Washington, DC. 112 p. [18987]
19. U.S. Department of the Interior, Fish and Wildlife Service, Region 1. 1991. Proposed determination of critical habitat for the northern spotted owl. keyw HABITAT, SPOTTED OWL, NORTHERN SPOTTED OWL, MGMT, [18988]
20. Verner, Jared. 1980. Bird communities of mixed-conifer forests of the Sierra Nevada. In: DeGraaf, Richard M., technical coordinator. Management of western forests and grasslands for nongame birds: Workshop proceedings; 1980 February 11-14; Salt Lake City, UT. Gen. Tech. Rep. INT-86. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station: 198-223. [17906]
21. Federal Register notice. 1992. U.S. Forest Service (USFS). Federal Register. July 31, 1992: 33934. [18989]
22. Donohoe, Robert W. 1974. American hornbeam Carpinus caroliniana Walt. In: Gill, John D.; Healy, William M., eds. Shrubs and vines for northeastern wildlife. Gen. Tech. Rep. NE-9. Upper Darby, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station: 86-88. [13714]
23. U.S. Department of the Interior, Fish and Wildlife Service. 1994. Endangered and threatened wildlife and plants. 50 CFR 17.11 & 17.12. Washington, DC: U.S. Department of the Interior, Fish and Wildlife Service. 42 p. [24413]
24. U.S. Department of the Interior, Fish and Wildlife Service. 1994. Endangered and threatened wildlife and plants; animal candidate review for listing as endangered or threatened species; proposed rule. 50 CFR Part 17. Tuesday, November 15, 1994. Federal Register. 59(219): 58982-59028. [24357]
25. Washington Department of Wildlife. 1994. Species of special concern in Washington - state and federal status. Olympia, WA: Washington Department of Wildlife. 41 p. [25414]
26. Committee on the Status of Endangered Wildlife in Canada. 1992. Canadian species at risk. Ottawa, ON. 10 p. [26183]
[26183] Index
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Related categories for Wildlife Species: Strix occidentalis
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