Very easy species to sex visually in adult plumage.

Besides the cock's being a much brighter blue than the hen, the easiest way to tell the sex is by comparing the amount of blue on the head.

This is very easy when viewing the birds from the top (cock left) When young fledge, for the first few days the sexes are fairly easily distinguished by comparing the amount of blue in the face and on the breast, with cocks being twice as bright as hens. It's advisable to ring them at this stage, as within a week or so it's very hard to tell the sexes apart until the adult plumage starts coming through.