Effects of predation by introduced mammals and mortality due to severe floods on population viability of the endangered Blue Duck (Hymenolaimus malacorhynchos)

Abstract

Predation by introduced species and anthropogenic climate change now are two major threats to avifaunae worldwide. We developed an age-structured, stochastic simulation model to perform a population viability analysis for the Blue Duck, or Whio (Hymenolaimus malacorhynchos), an endangered waterfowl endemic to the upland rivers of New Zealand. Demographic responses to six predator-control and flood-frequency scenarios were assessed to examine projected trends in long-term population dynamics and viability. A baseline analysis of abundance at current rates of predation by introduced mammals and mortality due to severe flood events indicated that the study population of Whio has only a limited probability of persistence during the next 100 years. Importantly, we found that the additive effects of population losses due to predation and a rising frequency of floods (as predicted by general circulation models) increased extinction risk by 69%. Our study demonstrates the urgent need for heightened control of invasive predators in Whio conservation areas, as well as informed consideration of future changes in regional climate patterns when planning management actions for Whio and other similarly threatened riparian species.