For the first time the unique coloured pattern of the iris of buttonquails (Turnicidae) is described. This unique pattern is due to the presence of a dark-brown crescent in the iris below the pupil, whose form and extent varies in response to light conditions. This dark crescent is present in the eyes of all individuals of Turnix species at every life stage, a consistency that has not been previously observed for the iridal marks found in other avian groups.

Human populations and breeds of domestic animals are composed of individuals with a multiplicity of eye (= iris) colorations. Some wild birds and mammals may have intraspecific eye color variability, but this variation seems to be due to the developmental stage of the individual, its breeding status, and/or sexual dimorphism. In other words, eye colour tends to be a species-specific trait in wild animals, and the exceptions are species in which individuals of the same age group or gender all...