The ruff has a 'lek' mating system, which means males of the species gather together and invest all of their energy into attracting females to mate with them, and none into parental care.

Within this specific mating system three distinct breeding behaviour types are easily identifiable. Territorial breeding males have spectacular plumes around their neck (which is why these birds are called ruffs) and head, and vary enormously in colouration so that each male is distinguishable. Nonterritorial so-called 'satellite' males, which are distinguishable by their white feathers, concentrate on stealing mates from the territorial displaying males. A third type of male, which is thought of as a 'cross-dresser', mimics females. They are able to hide from other males in the lek, so avoiding territorial aggression, and succeed by effectively stealing mates from the resident males.

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The study shows that the three distinct breeding behaviour types are encoded by a 'supergene' - a section of a chromosome containing a hundred or more genes.

Lead author Terry Burke said that the special feature of the supergene is that it allows lots of genes that are next to each other on a chromosome - which in this case determine multiple traits including hormones, feathering, colour and size - to evolve together and create two distinct behavioural traits.

The study appears in Nature Genetics.