POPULATION VIABILITY ANALYSIS FOR A SMALL POPULATION OF RED-COCKADED WOODPECKERS AND AN EVALUATION OF ENHANCEMENT STRATEGIES

We performed a series of population and pedigree analyses to examine t he viability of a small Red-cockaded Woodpecker (Picoides borealis) po pulation located at the Savannah River Site, in Barnwell and Aiken cou nties of South Carolina. The population's existence and future surviva l are precarious. As few as four individuals, including just one breed ing pair, comprised this population in 1985. Now, primarily because of experimental translocation of birds from other areas, the population has increased to 25. As of 1990, gene-drop pedigree analyses showed th at the respective contribution of 14 founders to the extant population has not been equal. Founder genome equivalents are low (5.4) but coul d reach 9.2 if poorly-represented founders were to produce offspring. The fraction of founder gene diversity retained in the current populat ion is 0.9 1. Successful recovery strategies would ensure 95% probabil ity of population survival while maintaining 90% heterozygosity for 20 0 years. Viability analyses indicated that, depending on relative effe cts of inbreeding depression and stochastic environmental events, the Savannah River Site population has a 68-100% chance of extinction duri ng this period. Annual translocation into the population of at least t hree females and two males for a 10-year period will achieve a 96% pro bability of survival for 200 years. Even with translocation of numerou s males and females per year (up to 50 of each), the 90% heterozygosit y goal may not be achieved. We discuss recommendations for choosing in dividuals for translocation, logistical constraints on achieving recov ery objectives, and limitations of our modeling approach.