The Blue Duck (Hymenolaimus malacorhynchus), also known as Whio (Maori), are a highly specialized waterfowl, inhabiting turbulent high country rivers in New Zealand. The male makes a distinctive high-pitched aspirate sound Ð ÒwhioÓ, contrasting with the guttural and rattle-like call of the female. They have a streamlined head and large webbed feet that enable them to feed in fast moving water. The upper bill has a thick semicircular, fleshy ÔlipÕ that overlaps the lower bill allowing them to scrape off insect larvae that cling to rocks, without wear and tear. Like many of New ZealandÕs endemic birds, the blue duck is struggling to survive in the face of introduced mammalian predation.