Endemic to New Zealand. Uniformly slate-blue duck with chestnut spotting on the breast. Bill is pale pink with a black tip. Males larger than females, with more breast spotting and more prominent green iridescence on the head, neck, and back. Found on clear, fast-flowing mountain streams. The Maori name, whio, is derived from the male’s high-pitched, wheezy whistle. Female’s call is a low rasping growl, often in response to disturbance. Readily distinguished from Pacific Black Duck or Mallard by uniform coloration and, if on the water, prominent tail tilted upward and head held erect.