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

Related categories for Wildlife Species: Strix occidentalis | Spotted Owl