MITIGATION OF HABITAT TAKE - APPLICATION TO HABITAT CONSERVATION PLANNING

One of the most important provisions of the U.S. Endangered Species Ac t precludes the ''taking'' of listed species on both public and privat e land. In past Endangered Species Act litigation, take has been broad ly interpreted to include the destruction or modification of habitats ns well ns the direct killing of animals. This requirement created an extensive burden on private landowners to provide habitats for listed species. This burden was substantially lessened when the ESA was modif ied in 1982 to allow incidental takings conditioned on preparation of a satisfactory ''habitat conservation plan.'' Because the majority of listed species are imperiled due to habitat modification, most habitat conservation plans must demonstrate defensible methods to mitigate ag ainst incidental habitat loss. A review of HCPs for the Northern Spott ed Owl (Strix occidentalis), and other species, indicates that mitigat ion solutions are often arbitrary lacking an empirical foundation in t he species' life history requirements Based on data from the Spotted O wl, we illustrate a biologically based method for estimating the areal requirements necessary to mitigate against the take of essential habi tats Toward this goal we adopt the concept of ''core area,'' that port ion of an animal's home range that receives disproportionate use. We e stimated core areas by means of the adaptive kernel density function a nd tested against a null distribution of animal use that assumes a biv ariate, uniform distribution of locations within the home range. The m ethod we illustrate, which is defensible, repeatable, and empirical, i s a clear improvement over the ad hoc methods used in many habitat con servation plans. Further, the methods we propose should be applicable to a large number of terrestrial species for which home range is a mea ningful concept.