After completion of post-juvenile moult, readily sexed based on the overall colouration of body and bill. Rarely, less jet-black males and darker females may cause temporary and mild difficulties, but should always be sorted out when given a more careful look.
Male, 3cy, March. Typical male with jet-black plumage and bright yellow bill. 2cy male may show extensive dark smudges to bill in spring, but most have turned yellow by the start of the breeding period. Note that a few (adult) male develop a deeper orange colour in bill. 
Male, 1cy, October. A few young males may be less jet-black with browner elements showing both in the upper- and underparts. However, overall coloration is still colder greysh black than females and very few (if any?) birds should cause any true problems. 
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