Recovery Plan for the Northern Spotted Owl - DRAFT

III.C.2. Management Guidelines for Federal LandsDesignated Conservation AreasDelineation of DCAsThe DCAs recommended on federal lands in this plan were derived from thehabitat conservation areas (HCAs) proposed by Thomas et al. (1990). Theobjective of the original HCA network was to establish habitat areas largeenough to support 20 pairs of owls with contiguous or nearly contiguous homeranges. The 20-pair goal was based on empirical evidence and on simulationmodeling which showed that clusters of 20 interacting pairs were likely topersist for at least 100 years. These areas were to be spaced a maximum of 12miles apart, edge-to-edge. The spacing guideline was developed to ensure thatjuvenile owls, dispersing from their birthplace, would be able to find suitablehabitat for nesting. Two-thirds of the juvenile owls studied at the time of theISC report had moved at least 12 miles. HCAs were as circular as possible tominimize the perimeter-to-area ratio.The 20-pair HCAs were termed category 1 HCAs. Where 20-pair areas couldnot be established, Thomas et al. (1990) recommended smaller areas capableof supporting two to 19 pairs. These smaller areas were termed category 2HCAs. The draft recovery plan adopts this convention for category 1 andcategory 2 DCAs. However, some of the category 2 DCAs have the capability ofsupporting only a single pair of owls.Thomas et al. (1990) used median annual home range size and density informationto determine the appropriate size for the category 1 HCAs. HCAs weredelineated to include the best available habitat and greatest number of knownpairs or territorial singles. This process was done iteratively to achieve the bestcombination of habitat, known owls, and HCA shape. Where category 2 HCAswere delineated because there was no opportunity to create category 1 HCAs,these smaller areas were spaced at a maximum distance of 7 miles. Approximately80 percent ofjuveniles that have been studied with radio transmittershave traveled at least this far (Thomas et al. 1990).The HCA network was modified slightly in the draft recovery plan using updatedinventories of owls and habitat (see Appendix I). Size and spacingcriteria were not changed. Boundaries were altered to improve the biologicaland/or economic efficiency of the system. The resulting DCAs are summarizedin Tables J. 1 through J. 11 in Appendix J.There were 196 DCAs identified for the DCA network, with 56 satisfying thecriteria for category 1 status. The remaining 140 areas are category 2 DCAs.To determine which DCAs met the criteria for category 1 status, the futurecapability of a DCA to support owl pairs on federal lands in the DCA wascalculated. This figure was determined by assuming that 80 percent of theland within the DCA would become suitable owl habitat over time. The actualcalculation is explained in Appendix J. In a few cases, where federal landscould support more than 15 pairs but not 20 pairs, the presence of existing owlpairs on nonfederal lands provided the basis for accepting DCAs as category 1.107