Recovery Plan for the Northern Spotted Owl - DRAFT

dbh) trees that varied in density from four to 14 per acre (Table B.2). No majordifferences were apparent between sites used for nests and sites used forroosting or foraging. Old-growth stands may have had slightly smaller averagecanopy cover than stands used by owls, however more detailed studies arenecessary to reach firm conclusions.Hardwoods comprised a large proportion of the trees less than 21 inches indbh and a smaller proportion of the larger trees (fable B.3). Snags were rare inthe studies in managed forests in the California Coast province (Folliard andReese 1991, Pious 1989, Kerns 1989) (Table B.4). In the Klamath province,snags in stands used by owls occurred at average densities similar to densitiesin old-growth stands. The average density of logs appeared to be similar in theCalifornia Coast and Klamath provinces.Three studies compared habitats used by roosting and foraging northernspotted owls (fable B.5). The studies provided data on canopy cover, size classdistributions of live trees, canopy closure, and numbers of snags. No differencesin the habitats used for roosting and foraging were detectable in thesestructural features. One study (Pious 1989) provided habitat data for bothnesting and roosting/foraging (fable B.6), and no differences were detectable inthe average number of large trees, canopy closure, or density of logs. Moresmall trees were present in roosting sites than in nesting sites.LaHaye (1988), Folliard and Reese (1991), and Pious (1989) compared measurementsfrom nest sites and from throughout the nest stand Cfable B.7).Average canopy closure, percent of trees that were hardwoods, and the densitiesof small and medium-sized trees were about the same in the stand and atnest sites. In the first two studies, fewer large trees were present, on average,in the stands than at nest sites. These data suggest that the owls in thesestudies selected average sites within stands except that utilized sites had morelarge (more than 36 inches dbh) trees.ITable B.2. Habitats used by northern spottd owls in the Klamath and CaliforniaCoast provinces. Values are the means from each study.Roosting Nesting,Nest and roosting, Old-Feature Value sites Roosting foraging foraging growthCanopy 8 1 a 8 6 b 84bclosure % 92c 9 3 d 8 4 e 8 0 f 9 1 9 8 0 h 9 5i 84i 65-801Trees/ac 5-10" 81C 6 9 d 8 7 e 9 2 f 959 12 4 h 100i 7 5kby dbh 11 -20" 51 65 37 39 36 42 60 -class 21-25" 23 19 17 18 15 14 14 ->35" 7 4 8 7 14 11 5 13aLaHaye (1988) (average of values for Klamath and California Coast provinces)bplous (1989)CFolliard and Reese (1991), and Diller and Folliard, (pers. comm.)dSelf, (pers. comm.)eBingham (1991) (Non-breeding season)gSolis (1983)hSsco (1990)iChavez-Leon (1989)JAsrow (1983)kKerns (1989) (Categories provided were 4-9' and 'old-growth." Most of the old-growth trees were >36' dbh.)Bingham and Sawyer (1991)..... - - - - I........... --.-- - , -I ..... I...................-295