Recovery Plan for the Northern Spotted Owl - DRAFT

distinguishing features are its dark eyes surrounded by tawny facial disks.Males and females are not easily distinguishable by plumage characters,although Barrows et al. (1982) suggested that the sex of spotted owls can bedetermined from the number of tail bars. Moen et al. (1991) reported that thetail-bar technique is unreliable for sex determination. However, a spottedowl's sex is recognized readily by voice (Forsman et al. 1984; see voicedescription under Behavior) and size (Forsman et al. 1984, Blakesley et al.1990). Spotted owls, and owls in general, show reversed sexual dimorphism:females are larger than males (Blakesley et al. 1990:323). This reversedsexual dimorphism exists in all commonly measured physical features, butbody mass is the single best physical predictor of sex in this owl (Blakesley etal. 1990:323).Plumage characteristics can be used to distinguish among several age classesof spotted owls. Juvenile spotted owls (ages 1 day to approximately 5 months)are distinguished by visible down feathers (Forsman 1981). The proportion ofdown feathers decreases with age. Subadult birds are distinguished by thepresence of adult plumage and white-tipped, pointed tail feathers (Forsman1981). In northern spotted owls, two subadult age classes can be recognized.Subadults that are 1 year old have a downy tuft at the tip of the pointed tailfeathers, whereas this downy tuft is lost by a bird's second year (Moen et al.1991). Adult (i.e., more than 27 to 28 months old) birds have rounded tips onthe tail feathers, which usually are mottled in color.Range And DistributionThe range of a species is that general geographic area within which the speciesmay occur. A species' distribution may be synonymous with its range or itmay be specific to the habitat types in which it occurs within its range. Northernspotted owls are found from southern British Columbia, Canada, south toMarin County, California. They range eastward through this area to the edgeof the Palouse prairie in Washington and the Great Basin shrub steppe inOregon and California. Although northern spotted owls are sighted in almostall areas of their general range (e.g., urban areas, beach dunes), their breedingdistribution is restricted to forest communities (see Habitat). They are foundfrom sea level to as high as approximately 7,500 feet in the southern portion oftheir range and to approximately 4,000 feet in elevation in the northern part oftheir range. Densities of owls vary across this broad range according to habitattype, habitat quality, and habitat quantity (Thomas et al. 1990). The currentdistribution of known spotted owls within their historic range is in Figure 2. 1.Taxonomy And Genetic RelationshipsSpotted owls are members of the largest family, Strigidae, within the orderStrigiformes. Some controversy exists regarding the taxonomic and systematicrelationships of birds within this order (Sibley et al. 1988, Cracraft 1981),although most of the discussion centers on higher taxonomic levels. Thegenus Strix is a widely distributed group of owls with members occurring in theNearctic, Palearctic, Neotropical, and Indian fauna regions (Clark et al. 1978).In North America there are three species of Strix: the spotted owl, the barredowl (Strix varia), and the great gray owl (Strix nebulosau Johnsgard 1988). Strixowls may be most closely related genetically to owls in the genus Athene (Randietal. 1991).Spotted owls were described by early naturalists as three subspecies (thenorthern spotted owl: the California spotted owl, Strix occidentalis occidentalLs;and the Mexican spotted owl, S. occidentals lucida). The California spotted owlwas first described by Xantus (1859) from a specimen collected in the12