Recovery Plan for the Northern Spotted Owl - DRAFT

__-_ __- ------ - -Table B.10. Average values for characteristics of sites used by northern spottedowls in the California Coast and Klamath provinces.dbh Number of Percent of understory(inches) trees per acre trees that are hardwoods5.0 - 10.9 270 60-8011.0 - 20.9 Ž40 45-6521.0 - 35.9 Ž15 10-40Ž36 Ž2 0-10Table B.1 1. Relative use of stands with different tree sizes by transmittered northernspotted owls in the Klamath Province of California".Average dbhSeason Averages per bird >21" 5-21" c5" OpenBreeding % of territory 42 31 27 -(Mar-Sept) % of locations 84 14 2 -% of locations/acreb 30 6 0.4 -Non-breeding % of territory 45 30 11 2(Oct-Feb) % of locations 56 30 11 2% location/acreb 16 8 8 8'Data from Solis (1983) and Sisco and Guiterrez (1984).t (% of locations in habitat Yx")/(number of acres of habitat X)DiscussionStudies summarized in Thomas et al. (1990:195) show that considerablevariation exists within provinces in the amount of older forest in annual homeranges. The ratio maximum:minimum amount was 15.4 in California, 3.5 inthe Oregon Klamath province, 5.7 in the Oregon Coast Range, 10.7 in thewestern Washington Cascades, and 3.0 in the Olympic Peninsula. In California,some of the nests studied by Self and Brown (pers. comm.) had virtuallyno stands with mean dbh more than 24 inches.Several explanations for the large variation in amount of older forest withinhome ranges are possible, and they have different implications for the recoveryprogram. In general, the variation does not cause too much concern abouthow well DCAs will function, but -does cause considerable concern aboutguidelines for avoiding 'take" that suggest preserving amounts of habitataround individual pairs that equal the median amounts that have been recordedin home ranges. This point is illustrated the by following hypotheses toexplain the high degree of variation observed in amount of habitat within homeranges.1. Owls with more older forest had higher fitness.303