EFFECTS OF NILE PERCH (LATES-NILOTICUS) INTRODUCTION INTO LAKE VICTORIA, EAST-AFRICA, ON THE DIET OF PIED KINGFISHERS (CERYLE-RUDIS)

In recent years the ichthyofauna of Lake Victoria, the world's largest tropical lake, has gone through dramatic changes. The population of Nile perch, a large predator which has been introduced into the lake by man, increased explosively at the expense of many haplochromine cichlid species. At the same time, numbers of a small cyprinid (dagaa) rose sharply. Previously Pied Kingfishers on Lake Victoria fed mainly on haplochromines. Only the youngest nestlings depended on dagaa as primary food. The current diet of adult birds clearly reflects the changes which have occurred in the fish community. Pellet analysis reveals a shift towards a diet composed of almost 100% dagaa. The change in prey species composition has increased the number of fish a kingfisher needs to catch daily in order to meet its energetic demands, because: (1) the mean size of haplochromines is larger than that of dagaa; (2) the mean size of dagaa has decreased since the increase in Nile perch; (3) the weight of dagaa is lower than that of haplochromines of equal size; (4) mainly juvenile dagaa and adults in poor condition are accessible to kingfishers.