Two decades of research and monitoring of the northern spotted owl on private timberlands in the redwood region: What do we know and what challenges remain? In: Standiford, Richard B.; Weller, Theodore J.; Piirto, Douglas D.; Stuart, John D, technical coordinators
This article is part of a larger document. View the larger document here.Abstract
Surveys for northern spotted owls on Green Diamond Resource Company's (formerly Simpson Timber Company) ownership in coastal northern California were initiated in 1989. The following year, a long-term demography study was initiated that has continued to the present time. A Habitat Conservation Plan was developed for the species in 1992 and numerous habitat studies followed. The extensive dataset generated was used to estimate the trend in owl numbers, develop resource selection functions for nighttime activity and nesting habitat, and analyze the factors influencing spotted owl survival, fecundity and habitat fitness (i.e., ability of the habitat to support a stable population of owls). Important conclusions generated to date include that habitat heterogeneity (i.e., juxtaposition of young and older stands) is critical to both survival and fecundity, as is precipitation during the early nesting season. A landscape projection of current and future habitat indicated an abundance of high quality habitat that has the potential to support an increasing population of owls. Demographic analysis found the owl population was stable from 1990 to 2001, but has declined in recent years. The decline coincided with an apparent increase in barred owls. Growing evidence including barred owl removal experiments indicate that the invasion of barred owls into northern California is responsible for the decline. Preliminary results of the recently initiated removal experiment suggest that control of barred owls is feasible, and that spotted owls respond rapidly and favorably where barred owls are removed.