Citation:

Dunk, J., B. Woodbridge, N. Schumaker, E. Glenn, B. White, D. LaPlante, R. Anthony, R. Davis, K. Halupka, P. Henson, B. Marcot, M. Merola-Zwartjes, B. Noon, M. Raphael, J. Caicco, D. Hansen, M. Mazurek, AND J. Thrailkill. Conservation planning for species recovery under the Endangered Species Act: A case study with the Northern Spotted Owl. PLOS ONE . Public Library of Science, San Francisco, CA, 14(1):e0210643, (2019). https://doi.org/10.1371/journal.pone.0210643

Impact/Purpose:

The development of recovery plans for listed species should be a scientifically rigorous and transparent process. Additionally, the analytic tools and forecasting models used in these activities must be supplied with the best available biological data and incorporate the knowledge of species experts. But in spite of the effort that goes into their development, few people actually read recovery plans, and fewer still review the detailed appendices in which the analytic processes are spelled out in detail. This manuscript tells the story of the development of the latest US Fish and Wildlife Service recovery plan for the Northern Spotted Owl. Our intent here is to reach out to a larger audience by publishing this material in a mainstream peer-reviewed journal. We hope as well to demystify the development process and also to provide a roadmap for others who will be developing the recovery plans of the future.

Description:

The northern spotted owl (Strix occidentalis caurina) was listed as threatened under the U.S. Endangered Species Act (ESA) in 1990. We applied modern spatial conservation theory and models to evaluate several candidate critical habitat networks, and sought an efficient conservation solution that encompassed the highest value lands for spotted owl recovery rather than maximizing the total area of potential critical habitat. We created a map of relative habitat suitability, which served as input to the spatial conservation prioritization program Zonation. We used the spatially-explicit individual-based population model HexSim to estimate and compare simulated spotted owl population outcomes among a suite of candidate critical habitat networks that varied in size and spatial arrangement under alternative scenarios of future habitat suitability and barred owl (S. varia) effects. We evaluated simulated spotted owl population outcomes, including total population size, and extinction and quasi-extinction likelihoods for 108 combinations of candidate critical habitat networks by habitat change by barred owl scenarios, both range-wide and within 11 distinct portions of the owl’s range. Barred owl encounter rates and the amount and suitability of habitat had substantial effects on simulated spotted owl populations. When barred owl encounter rates were high, changes in the amount and suitability of habitat had minimal impacts on population performance. Under lowered barred owl encounter rates, candidate critical habitat networks that included most existing high suitability habitat supported a high likelihood of long-term population persistence. Barred owls are currently the primary driving force behind poor population performance of NSOs; however, our models demonstrated that a sufficient area of high suitability habitat remains essential for recovery when effects of barred owls can be reduced. The modeling approach we employed is sufficiently flexible to incorporate new information about spotted owls as it becomes available and could likely be applied to conservation planning for other species.

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