Avifaunal sexual dimorphism

… or, the difference between girl birds and boy birds.

Golden Whistler (dimorphic)

The visual difference between male and female birds is very obvious in some species. The sombre grey tones of the female Golden Whistler are so completely different from the visually striking gold, black and white of the male.

Chestnut Teal (dimorphic - and the female has two legs😊)

The female Chestnut Teal has mottled brown feathers with a grey edge, a pale white throat patch, and lacks the iridescent green head of the male.

When the sexes are visually different in the bird world, it is mostly the male that is more colourful or at least visually brighter than the female (but not always – see later). Sexual dimorphism is the condition where different sexes of the same species exhibit differences in form, size, colour or structure. Sometimes the differences can be very minimal or subtle, and easily missed.

Crested Pigeon (monomorphic but some males might have a longer crest)

About half the world’s birds exhibit sexual dimorphism. The other half are monomorphic – the sexes are similar. Field guides will often describe monomorphic species as “sexes are similar” or sometimes, “sexes are similar, females duller”. In some field guides, no attempt is made to distinguish between male and female monomorphic species, just ‘adult’ and ‘juvenile’ differences might be explained.

Large-billed Corella (monomorphic)

A very few species of birds exhibit reverse sexual dimorphism (RSD) that is, the female is visually more colourful/brighter than the male.

Eclectus Parrot - Moonlit Sanctuary (reverse sexually dimorphic)

The Eclectus Parrot from Cape York Peninsula is a reverse sexually dimorphic species. The male is uniform emerald green with scarlet underwings. The female is a striking scarlet and blue bird.