Recovery Plan for the Northern Spotted Owl - DRAFT

Hamer (pers. comm.) described 11 nest sites in Mt. Baker-Snoqualmie NationalForest. Nest sites were described using a circular, 0.5-acre plot centered onthe nest tree.Meyer et al. (1992) studied relationships between habitat quality and variousdemographic measures on BLM land in southern Oregon and the borderbetween the Klamath and Oregon Coast provinces. They selected 50 nest sitesthat each had been visited at least four times in each of 5 years. Habitats weredefined using age and other features. Amounts of each habitat within 2.1miles of the nest were measured. Several other variables (e.g., elevation,fragmentation indices) were also recorded.Spies et al. (1988) quantified the stand structure in 85 old-growth Douglas-firstands in the western Washington Cascades, western Oregon Cascades, andOregon Coast Range provinces. Most study sites were in the Western HemlockZone and the lower elevation of the Pacific Silver Fir Zone; some sites were inthe Mixed Conifer Zone and the Sitka Spruce Zone. Douglas-fir was thedominant species in all stands, although western hemlock was codominant insome stands. During 1983-1984, vegetation was sampled in five nestedcircular plots per stand, spaced 325 feet or 490 feet apart depending on standsize (range 10 to 50 acres). Nested plots included 0.1-acre, 0.25-acre, and 0.5-acre plots.Structural Features of Sites Used by OwlsResultsRelatively few descriptions of stand structure at owl sites were reported byThomas et al. (1990). In the past 2 years, however, several new studies haveappeared. We tabulated this information from studies in the Thomas et al.(1990) as well as from the more recent reports. Most studies recorded measurementsat specific sites, as determined by radio-telemetry methods or byvisually locating the bird. A few studies also recorded measurements fromlocations placed randomly with the stand. We refer to the latter as standmeasurements; all other data in the tables are from specific sites used by owls.We report average values from each study for abundance of trees by size class(all trees and hardwood understory), canopy cover, and abundance of snags.Where possible, results are presented separately for nesting, roosting, andforaging and for breeding and nonbreeding seasons. We emphasize that therange in values in our tables is not the range of average values on individualterritories. Owls occurred in a much broader range of conditions than therange of values in our tables.Many of the studies reported indicators of variability (e.g., ranges, standarddeviations), but in most cases they were difficult to interpret because theydepend strongly on plot sizes and sample sizes. The range (or standard deviation)of values from small plots generally will be larger than the range (orstandard deviation) from large plots in the same area. Furthermore, manyinvestigators combined plots across home ranges in calculating their measuresof variability. The parameter (i.e., quantity of interest), in this case is difficultto describe in biological terms. We therefore report only the average valuesfrom each study, while recognizing that information on variability also wouldbe of value.294Klamath and California Coast provinces: Average canopy cover was 80percent or more in all studies (Table B.2). The average number of trees/acre,by size class, also was quite consistent except for large (more than 36 inches