After the cutscenes when you have finished catching leaves at the temple for the first time, go back and try it again. If you catch 4 leaves all together (not in a row but actually all at the same time), you will hear a 'quack' and a feather will drop from the tree. Catch it (be ready because it's fast!) and Ryo will notice a duck in the tree. Choose 'catch' from the selections that appear and then watch a funny (if not incomplete) cutscene. The duck will then be yours for use in the duck races.