Size and flight capability of Anas chathamica, an extinct duck from Chatham Island, New Zealand

Abstract

Measurements of major bones from Chatham Island’s extinct duck Anas chathamica (formerly placed in Pachyanas) were used to estimate the duck’s likely mass and flight capability. Mass estimates derived from published regression equations relating least femur circumference to body mass for volant birds ranged between 1,500–2,300 g, and those based upon tibiotarsus least circumference ranged between 1,670–2,400 g, providing an overall average mass estimate of c. 1,900 g. The bimodal size-frequency distribution of femur lengths, used to establish putative sexes, indicated a c. 11% sexual body mass dimorphism. Distal wing bones were disproportionately short when compared with flighted Anas ducks, and were similar to those of the related, flightless Auckland Island Teal A. aucklandica and Campbell Island Teal A. nesiotis. A humerus length/femur length ratio of c. 1.40 is below the lowest ratio recorded for any flighted Anseriformes (c. 1.60), and also lower than those for flightless steamer ducks Tachyeres sp. (c. 1.50), but above that of three flightless Anas sp. (c. 1.30). Carina (keel) area relative to carina or sternum length was less than for any flighted New Zealand Anas sp. but greater than for the Auckland Island and Campbell Island Teals. In combination, these characteristics indicate that the Chatham Island Duck was flightless, and also the largest known of its genus.