Endemic to New Zealand, the rare blue duck (Hymenolaimus malacorhynchos) is named for its unique slate-blue and lead-grey plumage which helps them hide by looking just like river boulders. Its native Māori name, whio is onomatopoeic, directly imitating the distinctive high-pitched whistling call made by the male ducks. They only live in very clean water – mainly in the mountainous regions of NZ – with lots of tiny stream insects, so their presence proves a river is healthy.
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