Viable Populations of Spotted Owls for Management of Old Growth Forests in the Pacific Northwest

The Northern Spotted Owl (Strir oc.c*idcwtcrlis (*( i ; i r i / i~ Xantus I 859) hiis become a surrogate for efforts to preserve rcmaining old growth forests in the Pacific Northwest. We review here il viability iinalysis prcpiired by the U. S. Forest Service which evaluates risks of extinction resulting separately from ( a ) stochastic demographic processes, (b) inbreeding and loss of genetic variability, and (c) habitat loss. Stochastic demography must include density dependence to be realistic, particularly for a territorial species. Because of high sampling variance, i t is unlikely that adequate data can be accuniulated for most rare species to provide demographic projections that differ significantly from a constant population. A model that integrates all components of the Forest Service viability analysis predicts a low probability that Spotted Owls will go extinct under the Forest Service’s preferred management alternative. However, we emphasize that such a model is unrealistic because i t does not incorporate spatial distribution of owls, and population fragmentation imposes the greatest risk of their extinction. A metapopulation model by Lande (1988) estimates acreage of old-growth forest necessary to preserve the Spotted Owl on Spotted Owl Habitat Areas (SOHAs). However, such estimates are dependent upon accurate determinations of the proportion of SOHAs and other habitats that are truly suitable for Spotted Owls. Habitat requirements of the owls must be carefully documented to justify management based upon the metapopulation model. Pages 133 135. Ecosystem Management: Rare Species and Significant Habitats. New York State Museum Bulletin 47 1. 1990.