Sacramento Fish & Wildlife Office
Species Account
California Spotted Owl
(Strix occidentalis occidentalis)
CLASSIFICATION: U.S. Forest Service Sensitive Species
On June 21, 2005, the Service announced a 90-day finding on a petition to list the California spotted owl (Strix occidentalis) as threatened or endangered under the Endangered Species Act (Federal Register 70:3560, pdf).
After review of all available scientific and commercial information, we found that the petitioned action is not warranted. (Federal Register notice 71:29886 pdf; May 24, 2006) News Release
RECOVERY PLAN: none
DESCRIPTION:
Spotted owls are medium-sized brown owls. They have brown eyes, round heads without ear tufts, and white spots on their heads, necks, backs and underparts. They have white and light brown bars on their wings and tail. Adults range from 16 to 19 inches (41 to 48 cm) in length, and have wingspans of 42 to 45 inches (107 to 114 cm).
Sexes cannot be distinguished by plumage, but can be readily identified by size and vocalization. Females are usually larger than males, with females weighing 19 to 27 ounces (535 to 775 grams) and males weighing 17 to 24 oz (470 to 685 grams).
The California spotted owl is one of three recognized subspecies of spotted owls. It is intermediate in color between the darker northern spotted owl (S.o. caurina) and lighter Mexican spotted owl (S. o. lucida). The size of the spots of the California spotted owl is also intermediate between the larger spots of the Mexican subspecies and the smaller spots of the northern subspecies.
Spotted owls generally reach reproductive maturity at two years of age. They are monogamous and generally pair with the same mate from year to year. The breeding season extends from mid-February to mid-September or early October.
Egg laying peaks in mid-April. When egg laying begins, the female spends almost all her time in the nest and the male supplies almost all of her food. The number of eggs in clutches ranges from one to four, with most nests containing two. Eggs hatch after approximately 30 days and most chicks fledge 34 to 36 days after hatching.
California spotted owls are generally nonmigratory, remaining within the same home ranges year round. However, in the Sierra Nevada, some individuals migrate downslope to winter ranges.
Spotted owls are "perch and pounce" predators, hunting primarily by selecting an elevated perch, detecting prey by sight or sound, and swooping from the perch to capture the prey with their talons. They forage primarily at night, but have been observed hunting during the day, especially while raising young. Spotted owls prey mainly on northern flying squirrels and dusky-footed woodrats. Other prey species include gophers, mice, squirrels, shrews, moles, bats, birds, frogs, lizards and insects.
DISTRIBUTION:
The California spotted owl still occurs throughout its historic range in California, extending along the west side of the Sierra Nevada from Shasta County south to Tehachapi Pass, and in all major mountains of southern California, including the San Bernardino, San Gabriel, Tehachapi, north and south Santa Lucia, Santa Ana, Liebre/Sawmill, San Diego, San Jacinto and Los Padres ranges.
In addition, a few sites have been found on the eastern side of the Sierra Nevada and in the central Coast Ranges at least as far north as Monterey County. For regulatory purposes, we established the Pit River as the boundary between the northern spotted owl and the California spotted owl (Federal Register 55:26114).
THREATS:
Spotted owl habitat is being adversely affected by wildfire, fuels-reduction activities, timber harvest, tree mortality and development. However, these adverse affects are not all additive. Fuels reduction activities have an immediate effect but reduce the risk of catastrophic wildfire in the long term.
It appears that even with losses of habitat from the above causes, spotted owls will still have sufficient quality and quantity of nesting, roosting, and foraging habitat, as well as forested areas through which they can disperse throughout the Sierra Nevada, for the foreseeable future.
Historically, the barred owl (Strix varia) was native to eastern north America and absent from the range of the California spotted owl. Barred owls have expanded their range into western North America, moving into the range of the California spotted owl from the north. Barred owl populations in California are increasing. In our 90-day finding (above), we noted that barred owls had expanded their range 200 miles southward in the Sierra Nevada over the past two years.
Barred owls occasionally hybridize with spotted owls, but this takes place mostly when barred owls move into new areas. It declines as barred owls become more numerous and have more access to other barred owls.
Although barred owls may pose a substantive threat to California spotted owls at some point in time, they do not appear to pose a significant threat now or in the foreseeable future, to the continued existence of the California spotted owl such that it warrants listing.
West Nile Virus was first detected in the United States in 1999 in New York, and has quickly spread to the western United States. The virus has not yet been detected in spotted owls.
In 2004, researchers in California took blood samples and oral swabs from captured spotted owls to test for the presence of West Nile virus and its antibodies. None of the spotted owls tested positive for WNV exposure. See the University of California Davis web page Potential Effects of West Nile Virus on California Wildlife
REFERENCES FOR ADDITIONAL INFORMATION:
Gutiérrez, R. J., A. B. Franklin, and W. S. LaHaye. 1995. Spotted Owl (Strix occidentalis). In the Birds of North America, No. 179 (A. Poole and F. Gill, editors). The Academy of Natural Science, Philadelphia, and The American Ornithologists' Union, Washington, D.C.
U.S. Fish & Wildlife Service. 2003. Endangered and Threatened Wildlife and Plants; 12-Month Finding for a Petition To List the California Spotted Owl (Strix occidentalis occidentalis). Federal Register 68:7580.
U.S. Fish & Wildlife Service. 2005. Endangered and Threatened Wildlife and Plants: 90-Day Finding on a Petition To List the California Spotted Owl as Threatened or Endangered. Federal Register 70:35607.
U.S. Fish & Wildlife Service. 2006. Endangered and Threatened Wildlife and Plants; 12-month Finding for a Petition to List the California Spotted Owl (Strix occidentalis occidentalis) as Threatened or Endangered. Federal Register 71:29886
Verner, J., K. S. McKelvey, B. R. Noon, R. J. Gutiérrez, G. I. Gould, Jr., and T. W. Beck. 1992. Assessment of the current status of the California spotted owl, with recommendations for management. Pp. 3-26 in the California Spotted Owl: a technical assessment of its current status (J. Verner, K .S. McKelvey, B. R. Noon, R. J. Gutiérrez, G. I. Gould, Jr., and T. W. Beck, technical coordinators). General Technical Report PSW-GTR-133, U.S. Forest Serv., Albany, CA.
Photo Credit: U.S. Forest Service
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