Evaluating Population Viability and Conservation Options for the Endangered Puaiohi
Evolution in the Hawaiian Islands has produced a unique assemblage of forest birds. Unfortunately, many of these species are highly endangered or extinct. Despite numerous threats and great effort aimed at saving endemic birds, we lack basic science necessary for understanding many species of concern, including the endangered puaiohi (Myadestes palmeri). Currently, the puaiohi’s breeding population is estimated at 500 birds restricted to the Alaka‘i Wilderness Preserve on Kaua‘i. Given its small population and restricted range, it is essential to understand conditions that affect the species’ population dynamics. Using all demographic data collected on the species, the goals of this study were to investigate links between weather conditions (precipitation and temperature) in the puaiohi’s range and reproductive success; represent puaiohi population dynamics under current and potential management scenarios to determine management’s potential efficacy in aiding species recovery; and investigate which management activities might supply the most cost-effective management of the species. Management scenarios modeled included rat management, habitat improvement (via habitat restoration or supplemental feeding), provision of nest boxes, and translocation of an additional population to another island. Results indicated that total rainfall in the previous wet season and mean rainfall during the breeding season positively correlated with most nest success variables. Female and juvenile survival were the parameters that most influenced estimates of population viability, so management should focus on increasing female and juvenile puaiohi survival. Rat control, even at conservative levels, was the most effective method of increasing puaiohi abundance. Furthermore, while translocation offers hope of increasing puaiohi population and decreasing extinction risk, success depends on the conditions established at the release site. In addition, re-establishment of the puaiohi captive breeding program may be necessary to provide enough birds to translocate, as the current wild population may not be productive enough to sustain harvest levels needed to successfully establish a new population. In total, management costs ranged from $378,701 to $245,213,905. Translocation was one of the most cost-effective means of managing puaiohi and supplemental feeding the least. Cost-efficiency of rat control varied based on scale and method, and restoration of habitat was moderately cost-effective. Findings indicate that practical, attainable management activities can increase puaiohi and bring it back from the brink of extinction. However, given weather conditions in the puaiohi’s range may shift with climate change, it remains important to invest in sound, science-based management to most efficiently manage the remaining population. These findings provide a model for other endangered species conservation efforts.