Onced aged correctly, most birds are sexed according to the below.
2cy: 2cy males are similar to 3cy+ males (see below) but often show a slightly less distinc pattern in face. Females have no or rather little black on crown, often a dirt grey forhead and some white admixed in the black chin.
3cy+: Males show a pure white foread and a glossy black crown reaching far down the nape and is distinctly demarked towards the pale grey mantle. Black chin lack any white feathers and face pattern is very contrasting in pure white and pure black. Females shows les black on head (not reaching down the nape) sometimes with some grey admixed. Forhead is generally white but with some grey feathers present. Face pattern often les distinct than in males.