Spatially explicit analysis of contributions of a regional conservation strategy toward sustaining northern goshawk habitat

Abstract

Setting aside habitat is a common strategy to maintain viable wildlife populations, but underlying assumptions or effectiveness are rarely evaluated. The Tongass National Forest prioritized habitat management for sensitive species in Southeast Alaska's rainforest, and standards and guidelines were established for northern goshawks (Accipiter gentilis). I used guidelines from other portions of its range and data from Southeast Alaska, USA, to evaluate the conservation strategy. I used published data and nests from this study to define choice habitats; published juvenile movements and female use areas were used to estimate an “average” post-fledging area and female breeding range, respectively. I used nest-tree locations (n = 136) to delineate corresponding virtual post-fledging areas and female home ranges, within which I calculated acreage of 4 cover-type and 4 land-use categories. About 30% of nests had >51% of post-fledging areas in choice habitat; 60% of nests had >51% in unsecure (unprotected from development) land-use designations, whereas 16% had >51% in a protected old-growth designation. The female range was similar to post-fledging areas, but the proportions predominantly (>75%) available for development (land use that modifies landscapes) or with 26–50% of total area in choice habitat were larger than post-fledging areas, and half as many nests had >51% of area in choice habitat. Among cover types, choice habitat averaged 39.4% of the post-fledging area. These findings increase uncertainty about conservation measures contributing sufficient habitat to sustain well-distributed, viable populations of northern goshawks throughout Southeast Alaska and demonstrate the need and feasibility of evaluating assumptions of conservation plans. © 2013 The Wildlife Society.