Polymorphism

A species is said to display polymorphism (or to be polymorphic) if it occurs in two or more distinct forms.(called morphs). If there are only two morphs, then we say that the species is dimorphic. An example is the Mountain Wheatear.

Blacm morph pf the male Mountain Wheatear illustrates polymorphism — Males of the Mountain Wheatear provide an example of a polymorphic species (actually dimorphic). The black morph male on the left is slightly more common than the grey morph on the left. Photographs by Tina Kennedy and Pam Kleiman

Grey morph of the male Mountain Wheatear llustrates polymorphism — Males of the Mountain Wheatear provide an example of a polymorphic species (actually dimorphic). The black morph male on the left is slightly more common than the grey morph on the left. Photographs by Tina Kennedy and Pam Kleiman

The article on polymorphsm in Wikipedia is well written!