Recovery Plan for the Northern Spotted Owl - DRAFT

Spotted Owl Prey 2timber harvest (Maser et al. 1978b). Hypogeous fungi form symbiotic relationshipswith the roots of coniferous trees, and these associations are importantto the overall health of the trees. The northern flying squirrel also consumesfungi (McKeever 1960, Maser et al. 1978b), at least seasonally, although itspends most of its time in the forest canopy. The flying squirrel also eatsepiphytic lichens that are abundant in the forest canopy. The northern flyingsquirrel, red tree vole, and red-backed vole comprise more than 75 percent ofthe diet of the spotted owl in the Oregon Cascades, so their dependence on theproduction of fir needles, fungi, and lichens in coniferous forest is important tothese food webs and the owl.The availability of energy for maintenance and reproduction is important to allorganisms, so to properly manage an animal, the ecology of its food sourcesmust be considered. Although dietary requirements of a predator may be metby a large range of sources, many species, and the spotted owl in particular,are selective in the prey they feed upon. Although a variety of species are eatenby the owl, only a few species make up the majority of the owl's diet within agiven region. More than 90 percent of the spotted owl prey consists of mammals(Forsman et al. 1984). Spotted owl diets and the habitat associations ofits prey were reviewed thoroughly by Thomas et al. (1990:20 1). This sectionsummarizes their report and adds recently published information that augmentstheir work.The diet of northern spotted owls varies regionally, but within a region it istypically dominated by two or three species (Thomas et al. 1990). Compositionof diets varies seasonally (Forsman et al. 1984) but appears to be stable overtime based on studies during different years (Thomas et al. 1990). Flyingsquirrels (Glaucomys sabrinus) and woodrats (Neotoma cinerea and N. fuscipes)dominate the diet in mesic and dry forests, respectively (Thomas et al. 1990).Snowshoe hares (Lepus americanus) and brush rabbits (Sylvilagus bachmantjtypically represent less than 10 percent of the prey based on number of preytaken, but because of their larger size, they have been reported to comprise upto 25 percent of the prey biomass (Forsman et al. 1984:43). Red tree voles(Phenoacomys longicaudus P. porno) and deer mice (Peromyscus maniculatus)may constitute more than 30 percent of prey numbers and more than 10percent of prey biomass regionally (Thomas et al. 1990). Western red-backedvoles (Clethrionomys californicus) usually comprise a smaller percent of the dietthan do red tree voles and deer mice, generally less than 5 percent of preybiomass (Forsman et al. 1984:41).Northern Flying Squirrels.-Northern flying squirrels have a broad distributionthroughout coniferous forests and are found in western Washington,Oregon, and northern California (Figure D.5.a). Flying squirrels are arborealmammals and are not resident in recent clear-cuts. They nest in many substrates,including cavities in live and dead trees. Density does not appear to bestrongly dependent on stand age alone. In the Oregon Coast Range, flyingsquirrels were more abundant in old-growth than in second-growth standsduring some, but not all, years of a study by Carey et al. (1992). Similardensities were reported in old-growth and second-growth stands in the OregonCascades (Rosenberg and Anthony 1992). In an ongoing study in true fir(Abies spp.) forests in Lassen National Forest (north-central California), preliminarydata suggest squirrel densities are markedly lower in an intensivelymanaged shelterwood cut than in young- and old-growth stands (J. Waters,U.S. Forest Service, Arcata, California, pers. comm.).2 Contributed by Daniel Rosenberg, Redwood Sciences Laboratory. U.S. Forest Service, Arcata, California367