Recovery Plan for the Northern Spotted Owl - DRAFT

if all habitats were available to the animal. Thus, we have many observationsof spotted owl habitat use, fewer studies of habitat selection, and no studies ofhabitat preference as defined by Peek (1986). Early studies portray the northernspotted owl as a denizen of primal forests (Grinnell and Miller 1944) basedon observations of habitat use. However, Grinnell and Miller (1944) found thatgeographic variation in habitat use did exist in spotted owls. Subsequentinvestigations (Forsman 1976, 1980, Solis 1983, Forsman et al. 1984,Gutierrez et al. 1984, Solis and Gutierrez 1990, Sisco 1990, Blakesley et al. InPress, Bart and Forsman 1992) reaffirmed the naturalists' notions from observationsof habitat use, but more importantly, provided analyses of habitatselection. Recent surveys of managed (i.e., previously logged private lands)forests have added to the knowledge of habitat use (Diller 1989, Irwin et al.1989a, 1989b, Kerns 1989, Pious 1989). These latter observations are important,but their ecological significance is enigmatic because, unlike studiesconducted on public land, there is no supporting demographic information. Itis essential that more demographic information be gathered to evaluate thesepopulations (see section on spotted owl use of young, managed timberlands).Variation in habitats used: Spotted owls are known to nest, roost, and feedin a wide variety of habitat types and forest stand conditions throughout theirdistribution (see discussion of suitable habitat elsewhere in this document).Spotted owls use western hemlock, mixed evergreen, mixed conifer, Douglasfir,redwood, Douglas-fir/hardwood, evergreen hardwood, ponderosa pine,western red cedar, and other forest types in different parts of their range. Mostobservations of spotted owl habitat use have been made in areas having acomponent of old-growth and mature forests (Solis 1983, Forsman et al. 1984,LaHaye 1988, Sisco 1990, Ward 1990, Zabel et al. In Prep.; see additionalsummaries in Thomas et al. 1990). However, observations of spotted owls inmanaged (i.e., previously logged) stands are commonplace (Diller 1989, Kerns1989, Pious 1989). Studies evaluating habitat selection show owl selection formature and/or old forest stands with concomitant selection against youngstands (Forsman 1980, Solis 1980, Carey et al. 1990, Blakesley et al. In Press).Selection for forest stands of intermediate age and size vary among the owlsstudied.Nesting habitat: Most northern spotted owl nest sites observed on publiclands have been located in old-growth or mature forests (Forsman et al. 1984,LaHaye 1988). In addition, the proportion of older seral stage forest surroundingnests has been significantly greater than it was in surrounding randomsites in the same area (Meyer et al. 1990, Ripple et al. 1991). In areas ofprivate managed forest, particularly in the California Klamath and CaliforniaCoast physiographic provinces, where some uneven-aged silviculture hasoccurred or where fast tree growth facilitates rapid habitat development,spotted owls are known to nest in managed stands, especially if residual oldgrowthcharacteristics are present (Forsman et al. 1977, Diller 1989, Pious1989, Thomas et al. 1990: see Appendix B).Spotted owls do not build their own nests; they depend upon suitable naturallyoccurring nest sites. In older-age forests, owls tend to nest in broken-top treesand cavities; they use platforms (i.e., abandoned raptor nests, squirrel nests,mistletoe brooms, debris accumulations) less frequently (Forsman et al. 1984,LaHaye 1988). In younger forests (i.e., forests less than 150 years old), nestsmore frequently are found on platforms (LaHaye 1988, Irwin et al. 1989a,Buchanan 1991). In one California study (LaHaye 1988), the proportion ofplatform nests used by spotted owls increased north to south, but the trendprobably is related to the distribution of stand ages in that study rather thanlatitude.The presence of suitable nest sites has been hypothesized as one possible basisfor the use of old-growth by spotted owls (Forsman et al. 1984). However, owls19