Observations on the behaviour and relationships of the White-backed Duck and the Stiff-tailed Ducks

Abstract

1. A number of behavioural and anatomical sources of evidence indicate that the White-backed Duck (Thalassornis) should be placed in the tribe Dendrocygnini and be regarded as a whistling duck rather than an aberrant Stiff-tailed Duck. 2. Behavioural evidence supports earlier views that the Black-headed Duck (Heteronetta) is the most generalized of the true stiff-tails, and it is suggested that the numerous unusual aspects of sexual behaviour found in this tribe can be traced back to a reduction of pair-forming and pair-maintaining mechanisms which can already be detected in Heteronetta. 3. The distinctive aspects of morphology and behaviour found in the Musk Duck (Biziura) can be attributed to the predictable effects of intense sexual selection resulting from the breakdown of pair bonds and the establishment of a completely polygamous or promiscuous breeding system in Biziura. 4. There is still too little behavioural information concerning the Masked Duck to advocate its generic separation (Nomonyx), although it is suggested that this species is probable the most isolated of the typical stiff-tails and presumably represents a less specialised evolutionary line than do the other stiff-tails of the genus Oxyura. 5. Recent behavioural evidence tends to support earlier views that the remaining five species of Oxyura fall into two broad evolutionary groups; including leucocephala and jamaicensis on the one hand, and maccoa, vittata and australis on the other.