A very difficult species to sex visually. For 100% accuracy surgical or DNA sexing is advised, however there are small differences in the sexes.

 
When viewed from the top the cock (on the right) appears to have a bigger, heavier bill than the hen. However the differences aren't always as obvious as in this pair.

In side profile the cock (top) appears to have a slightly bigger beak, but the more obvious difference is the shape of the upper-beak. Notice how it "hangs" over the lower-beak, whereas in the hen it forms a straight line.


The cock (left) also have a slightly bigger extension of the black area on the breast.