Sexual
Dimorphism
Dimorphism is the difference in appearance between the male and female birds of a species.
The differences in the genders could be extreme or just very slight, in the case of the greenfinch there is only a little colour difference (female is more drab), but with Paradise Shelducks there is a major change as the male is black, and the female is brown with a white head.
In some species (e.g. Birds of Paradise), gender selection comes into play, which is when females choose the prettiest or most active male to bond with. The bird's appearance portrays the best traits for fighting, breeding and showing off as the weak or less colourful males aren't selected by the females.
Lots of species in New Zealand are sexually dimorphic, but there are also many that are not; such as the Silvereye (aka Waxeye or Tauhou) or the Fantail (Piwakawaka), the male and female look exactly alike in those species.
By George Hobson