he Spotted Owl, Strix occidentalis, is a species of true owl. It is a resident species of forests in western North America, where it nests in tree holes, old bird of prey nests, or rock crevices. Nests can be between 13 and 66 yards (12 to 60 meters) high and usually contain two eggs (though some will contain as many as four). It is a strictly nocturnal owl, which feeds on small mammals and birds, which has only been discovered recently.
This owl has a length of 43 cm (17 inches), a wingspan of 114 cm (45 inches), and a weight of around 600 g (21 ounces). Its eggs are a little over 2 inches (50 millimeters) long, and are white and smooth with a slightly grainy texture. The female sits on the eggs and cares for the young, while the male provides food for them. Juvenile Spotted Owls have an average survival rate of 11%, with an average birth rate of .58 owls per pair.
Spotted owls occur in closed-canopy, uneven-aged, late-successional and old-growth forests ; Mexican spotted owls also occur in deep, steep-walled canyons with little canopy cover . Many habitat measurements were taken in plots between 0.1 and 2 acres (0.04-0.8 ha). In this section, these will be referred to as "small plots."
Spotted owls occur at a range of elevations, with higher elevations occupied at lower latitudes. Northern spotted owls occur at elevations from 70 to 6,600 feet (20–2,010 m), with the majority in the lower portions of this range . In coniferous forests of northwestern California, nest sites ranged from 118 to 4,944 feet (35-1,507 m), with 94% occurring below 4,000 feet (1,218 m) . In mixed evergreen and mixed-conifer forests of northwestern California, roosting northern spotted owls avoided areas above 2,950 feet (900 m) . In coniferous forests of the Klamath, Coast and Cascade regions in Oregon and the Olympic peninsula of Washington, nest locations were significantly lower (P<0.001) in elevation than random sites within northern spotted owl's home ranges . In coniferous forests of southwestern Washington, important owl locations (e.g., nest sites, multiple detection sites) averaged 3,170 feet (966.2 m), which was significantly (P<0.001) lower than the 3,510-foot (1,070.3 m) average elevation at random sites . In coniferous forests of the eastern Cascade Range of Washington, elevation of northern spotted owl nest sites was negatively associated with latitude (P<0.001) , and site occupancy and reproductive rates were inversely associated with elevation .
In some regions, northern spotted owls use areas near water. In mixed-evergreen forests of northwestern California, the summer roost sites of 10 northern spotted owls averaged 466 feet (142.1 m) from water, which was significantly (P<0.01) shorter than the average 743 feet (226.6 m) from random locations to water . In managed timberlands in the coastal redwood vegetation zone of northwestern California, northern spotted owl nest areas were closer to water than randomly-selected plots (P=0.032) . Nest sites in low- to mid-elevation conifer forests of northwestern California averaged 385 feet (117.3 m) from water . On 2 sites in the Coast and Cascade Ranges in western Oregon, 84% of nests were within 820 feet (250 m) of a stream or spring . In southwestern Oregon, roost sites were significantly (P<0.01) closer to water in summer (x = 240 feet (74 m)) than in winter (x = 325 feet (99 m)) . A literature review states that Mexican spotted owls occur in canyons with perennial water sources .
Spotted owl home ranges are generally large, but sizes are variable. The average home range size of northern spotted owl pairs varies from 1,030 acres (417 ha) in coniferous forests of Oregon  to 14,169 acres (5,734 ha) on Washington's Olympic Peninsula . In riparian hardwood forests of the Sierra National Forest, California spotted owl had comparatively small home ranges, varying from 661 to 985 acres (267-399 ha), while those in mixed pine, white fir, and California red fir forests of the Lassen National Forest had home ranges varying from 7,061 to 12,473 acres (2,857-5,048 ha) . Median California spotted owl pair home range sized up to 18,706 acres (7,570 ha) . A Mexican spotted owl review includes individual home range estimates from 645 acres (261 ha) in the upper Gila Mountains to 3,672 acres (1,487 ha) on the Colorado Plateau . Pair home range estimates ranged from 2,548 acres (1,031 ha) in Arizona to 2,780 (1,125 ha) in New Mexico . In some cases, Mexican spotted owls can spend a substantial portion of their time in a small portion of their home range . For example, in riparian areas, pinyon-juniper, and mixed-conifer woodlands of southern Utah, 70% of radio locations occurred within an area averaging 689 acres (279 ha), which is less than one-third of the 2,179 acre (882 ha) area that was occupied by 95% of radio locations .
Spotted owls do not build their own nests. They rely on sites such as trees and snags with cavities or broken tops, and platforms associated with abandoned raptor or squirrel nests, witches' brooms (caused by mistletoe infection) and debris accumulations . Large, old trees are most often used by spotted owls for nesting. Species used as nest trees vary with region and subspecies.
Several studies indicate that tree cavities are most commonly used for nesting by spotted owls, while the extent of platform use varies. In coniferous forests in Oregon, 60% to 93% of nests were in trees with broken tops. Additionally, broken-topped trees (>21 inches (53.3 cm) DBH with 1 or more secondary crowns) had significantly (P<0.001) higher basal area and density in small plots on and around nest sites than in random plots within spotted owls' home ranges . Platform use may be more common in areas that lack large, old trees and snags and have a greater abundance of witches' brooms. Compared to other habitats within their range, northern spotted owls use platforms more often in mixed-evergreen and mixed-conifer forests . California spotted owls in southern California use platforms more frequently than those in the Sierra Nevada . Platform use also occurred more frequently in oaks than in conifers in the southern Sierra Nevada . The average DBH of California spotted owl platform nest trees was significantly (P<0.01) smaller than that of cavity nest trees in foothill riparian and oak woodlands in the southern Sierra Nevada . In grand fir-dominated stands in eastern Washington, northern spotted owls nested in witches' brooms on trees as small as 12 inches (30 cm) DBH . Mexican spotted owls use cliffs and comparatively open areas as nest sites more frequently than the other subspecies . Fletcher and Hollis (1994, as cited by ) found 9.7% of 248 Mexican spotted owl nests in cliffs, while Steger and others  noted only 1 out of 41 California spotted owl nests in a rock cliff in the southern Sierra Nevada.
Spotted owls typically nest in old trees in mature and old-growth forests. Sixty-five percent of northern spotted owl nests sites in coniferous forests of Oregon were in trees greater than 120 years old . On 2 sites in the Coast and Cascade Ranges in western Oregon, 90% of nest sites were in unmanaged old-growth forests, 4% were in mature forests, and 6% were in late-successional forests (70–80 years) with 5 or fewer residual old-growth trees per hectare . In low- to mid-elevation coniferous forests of northwestern California, the minimum nest tree age averaged 288 years, with a range of 57 to 688 years . In coniferous forests in the Cascade Range of southwestern Washington, northern spotted owl site centers, such as the nest tree or locations of fledged young, did not occur in stands less than 49 years old, and 31% were in stands greater than 180 years old . Most species of nest trees used by nesting California spotted owls in oak woodland and coniferous forests of the southern Sierra Nevada averaged more than 227 years of age .