Determining Sensitive Parameters for the Population Viability of Reintroduced Sumatran Orangutans (Pongo abelii)

Although reintroduction has been a widely implemented conservation tool, in many cases it is unclear whether the released animals can successfully establish a viable and self-sustaining population. We constructed a population model for reintroduced Sumatran orangutans (Pongo abelii) and conducted a population viability analysis to evaluate the probability of persistence. We based our study on a reintroduced orangutan population at Bukit Tigapuluh, Jambi, Central Sumatra, Indonesia. We used various scenarios to assess the effects of adaptation time, number of released individuals, duration of release period, variation in infant survival, and carrying capacity on population extinction probability over time. We found that behavioral adaptation of individuals to living in the wild within < 6 yrs after release enhanced population persistence, and that initial losses may be compensated by additional releases. Our analyses indicated that a lack of information about released orangutans prevented accurate evaluation of the effectiveness of reintroduction procedures. Consequently, we recommend that reintroduction projects improve data quality on the fates of released individuals in order to provide a reliable basis for a population viability analysis. The use of population viability analyses would allow proactive management and a better evaluation of reintroduction progress.