A Dynamic Analysis of Northern Spotted Owl Viability in a Fragmented Forest Landscape

The Northern Spotted Owl (Strix occidentalis cau- rina) is closely associated witb mature and old-growth co- niferous forests in the Pacific Northwest There has been a rapid loss and fragmentation of this habitat over the last half century, which may jeopardize tbe long- term survival of the species through reduction of dispersal success. In this paper we report results of a population model for the North- ern Spotted Owl that incorporates both juvenile dispersal and search for mates. We analyze both deterministic and stochastic versions of the model in search of thresholds for population persistence related to search efficiency, popula- tion density, and amount of suitable habitat. In addition, we analyze the model under the nonequilibrium conditions tbat currently exist due to timber harvest in the owls' pre- ferred habitat. Our results predict a sharp threshold below which populations cannot persist, and suggest tbat infer- ences from population models that incorporate equilibrium assumptions may be highly misleading.