Abstract
The Rēkohu Chatham Islands, 785 km east of mainland Aotearoa New Zealand, exhibit high levels of species endemism. Prior to human settlement, the islands supported a rich waterfowl fauna comprising at least eight anatid species. Here we describe a new extinct duck from Holocene fossil bone deposits on the Chatham Islands. Geometric morphometric analyses and phylogenetic analysis of complete mitogenomes confirm that the Rēkohu shelduck (Tadorna rekohu sp. nov.) was the sister-taxon to the pūtangitangi paradise shelduck Tadorna variegata (Gmelin, 1789) from mainland New Zealand. The ancestors of the Rēkohu shelduck colonized the Chatham Islands around 390 000 years ago during the Late Pleistocene. Comparatively short, robust wing bones and long leg bones indicate that the species was flight-reduced relative to their mainland congener. The presence of Rēkohu shelduck bones in early Moriori midden deposits suggests its extinction was due to over-hunting prior to the later European and Māori settlement of the islands in the 19th century.