Post-copulatory display in fulvous and black-bellied tree ducks

The courtship display of tree ducks has been characterized as simple, resembling that of the swan (Delacour, 'Waterfowl of the World', vol. 1, p. 32, London, 1954). However F. Finn ('Bird Behaviour', p. 262, London, 1919) called attention briefly to the fact that "there is frequently a marked display after, but not before, pairing, both parties executing a step-dance in the water with one wing held aloft." So far as we know, this curious display has not been described in detail nor pictured.