SEX RATIOS, MORPHOLOGY AND GROWTH OF THE AFRICAN BUCK DUCK

Summary

Frost, P. G. H., Ball, I. J., Siegfried, W. R. & McKinney, F. 1979. Sex ratios, morphology and growth of the African Black Duck. Ostrich 50:220-233.

Black Ducks Anus sparsa were trapped regularly in the Eerste River Valley near Stellenbosch, South Africa. The sex ratio of adult Black Ducks did not differ significantly from parity. Males were larger and heavier than females and also had proportionately larger wing spurs which are used when fighting over mates and territories. Body mass fluctuated seasonally, being lowest during summer and highest in autumn-winter. In the southwestern Cape breeding took place from July to December after the peak of the early winter rains. Ducklings hatched when waters were dropping and there was an increase in the emergence of aquatic insects. The growth rate of ducklings in the Eerste River Valley was severely retarded compared with that of ducklings reared in captivitly. Black Ducks moulted their body feathers twice a year, the moults corresponding to the pre- and post-nuptial moults of northern hemisphere waterfowl. Moults were not accompanied by any change in plumage coloration. Body and rectrix moult took more than five weeks to complete while remex replacement required about 30 days. Males began wing moult about a month earlier than females which delayed moulting until after their young had been reared. Forty-six percent of Black Ducks trapped had noticeable plumage aberrations; individual recognition among Black Ducks appears to be an important element in their social behaviour.