SEX RATIOS, MORPHOLOGY AND GROWTH OF THE AFRICAN BUCK DUCK

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Abstract
Black ducks A. 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-Dec. 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 captivity. Black ducks molted their body feathers twice a year, the molts corresponding to the pre- and post-nuptial molts of northern hemisphere waterfowl. Molts were not accompanied by any change in plumage coloration. Body and rectrix molt took more than 5 wk to complete while remex replacement required about 30 days. Males began wing molt about a month earlier than females which delayed molting until after their young had been reared. Of black ducks trapped, 46% had noticeable plumage aberrations; individual recognition among black ducks may be an important element in their social behavior.