Recovery Plan for the Northern Spotted Owl - DRAFT

2. Population StatusThere are no estimates of the historical population size of the northern spottedowl, but owls are believed to have inhabited most old-growth forests throughoutthe Pacific Northwest and northwestern California, and they still are foundwithin their historical range in most areas where suitable habitat remains(Thomas et al. 1990).Northern Washington and southern British Columbia represent the northernextent of the range of the owl. Population densities and numbers are lowest inthese areas, with fewer than 20 pairs located in extensive surveys along theU.S. border with British Columbia (Dunbar 1990). A small, potentially isolatedpopulation of about 125 known pairs of spotted owls is located on the OlympicPeninsula in and around Olympic National Park (Fredrickson et al. 1989,Washington Department of Wildlife (WDW) 1991). Fewer than 50 owls havebeen located in recent extensive surveys in the Coast Ranges of southwesternWashington and northwestern Oregon north of Corvallis (Forsman 1986,Forsman et al. 1987, Irwin et al. 1989b, Oregon Department of Fish andWildlife (ODFW) 1991). Populations also decrease in size and density from theMendocino National Forest south to Point Reyes, California, and from theKlamath province east to the area of contact with the California subspecies inthe Sierra Nevada Range (Gould pers. comm.).Most of the present population of owls is found in the Cascades and Klamathprovinces in Oregon, and in the Klamath and Coast Range provinces in northwesternCalifornia (Advanced Sciences Inc. 1989, Beak Consultants 1989,Brown 1989, Diller 1989, Irwin et al. 1989c, Kerns 1989a and 1989b, Pious1989, ODFW 1991, WDW 1991). Distribution of remaining habitat is similar tothe present distribution of spotted owls.More than 86 percent of currently known pairs of owls has been observed onfederally managed lands. The distribution of these pairs varies widely by landownership, state, and physiographic province (Table 2.3). Although inventoriesare least complete in California, about 30 percent of the habitat and populationof spotted owls may occur in the Coast Range (Gould pers. comm.).Only population data gathered during a 5-year period were analyzed during thedevelopment of the recovery plan because they may provide more reliableestimates of actual numbers than longer cumulative periods or single-yearcounts, given the rapidly changing quantity and quality of habitat. It is alsothe period with the most intense inventories, and is within the average lifespan of the species (about 8 years). Depending on availability of data, theperiod used was either 1986 through 1990 or 1987 through 1991 (see Table2.3).Inventories from 1987 through 1991 indicate a total of about 3,500 knownpairs of northern spotted owls in Washington, Oregon, and northern California(Table 2.3). This number is a minimum estimate of the true population size.The actual number of spotted owls remaining is unknown.3. Significant Threats to the Northern Spotted OwlTable 2.4 provides a summary of significant threats to northern spotted owlpopulations by physiographic province. Threats were characterized as follows:Severe: The problem poses a severe threat to the population at thecurrent time or will pose such a threat within the next several generations.The likely consequence is failure to maintain a population distrib-33