Size and age/sex composition were recorded for social groups of seven ungulate species over two years. Most species showed seasonal changes which were correlated with rainfall or with their breeding cycle. Group sizes tended to increase during the rainy seasons, although some species, particularly wildebeeste, also aggregated strongly on fresh burns. For all seasonally breeding species, the average male had little contact with females during the conception peak, although female herds almost invariably had about one attendant male.