Chatham Island merganser

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Chatham Island merganser (Mergus milleneri) is an extinct duck from New Zealand. It lived from the late Pleistocene into the Holocene and is known only from fossil remains. The species was named to honor Dr. Philip Millener, who studied fossil birds.

It was the smallest member of the Mergus genus. Its skull and beak were smaller than those of the Auckland Island merganser, but it had larger salt glands. Most bones were about 3–6% smaller than those of the Auckland Island merganser. It could fly, but not as well as many other mergansers.

Fossils show it lived across Chatham Island, with nesting sites found in a cave on the Te Whanga Lagoon shore where adults, eggs, and nestlings were discovered. Its habitat likely included small lakes, slow peat-stained rivers, and lagoons.

The species was formally described in 2014, after previously being thought to be the Auckland Island merganser. Extinction was probably caused by human hunting, and possibly habitat loss and introduced predators such as Polynesian rats and dogs. Bones have been found in ancient human middens, showing it was hunted by people.