Using presence-absence data to build and test spatial habitat models for the fisher in the Klamath region, USA

Forest carnivores such as the fisher (Martes pennanti) have frequently been the target of conservation concern because of their association in some re gions with older forests and sensibility to landscape-level habitat alterat ion. Although the fisher has been extirpated from most of its former range in the western United States, it is still found in northwestern California, Fisher distribution, however, is still poorly known in most of this region where surveys have not been conducted. To predict fisher distribution acro ss the region, we created a multiple logistic regression model using data f rom 682 previously surveyed locations and a vegetation layer created from s atellite imagery. A moving-window function in a geographic information syst em was used to derive landscape-level indices of canopy closure, tree size class, and percent conifer. The model was validated with new data from 468 survey locations. The correct classification rate of 78.6% with the new dat a was similar to that achieved with the original data set (80.4%). Whereas several fine-scale habitat attributes were significantly correlated with fi sher presence, the multivariate model containing only landscape- and region al-scale variables performed as well as one incorporating fine-scale data, suggesting that habitat selection by fishers may be dominated by factors op erating at the home-range scale and above. Fisher distribution was strongly associated with landscapes with high levels of tree canopy closure. Region al gradients such as annual precipitation were also significant. At the plo t level, the diameter of hardwoods was greater at sites with fisher detecti ons. A comparison of regional fisher distribution with land-management cate gories suggests that increased emphasis on the protection of biologically p roductive, low- to mid-elevation forests is important to ensuring the long- term viability of fisher populations.