Effect of temperature and rainfall on the distribution of the South African shelduck Tadorna cana

Abstract

The distribution of the South African shelduck Tadorna cana was mapped and related to temperature and rainfall. A multiple regression analysis based on quantified spatial abundance (the number of sixteenth degree squares recorded with shelduck in a degree square), mean annual rainfall, mean annual temperature and mean temperature of the coldest (July) and hottest (January) months indicated a significant (P < 0,001) negative linear relation between shelduck distribution and temperature, but no significant (P > 0,05) relation with rainfall. Mean annual rainfall in excess of 600 mm is however suggested to bring about unfavourable habitat within temperate southern Africa. The hypotheses formulated on the environmental relations of shelduck distribution are compared with habitat preference, breeding season, nest sites and feeding behaviour.