How do you tell the difference of a baby duck male or a female?

Determining SexMale and female ducks, and most birds in general, have very different coloration. The pictures in a good bird book will show you these differences. Typically the male bird has brighter plummage then the female, one belief is this is to make the nest less obvious to preditors during the nesting season.

The male will also have a curling tail if it is a male.