The Gouldian finch are small, brightly colored birds with green backs, yellow bellies, and purple breasts with a light blue uppertail and a cream undertail. Sometimes called lady gouldians, their facial color can vary, but black is the most common. Gouldian finch chicks are equipped with blue
phosphorescent beads along their mouths, making it easy for the parents to feed them in the darkness of the nest cavity.
Photo credit: Greg Grall/National Aquarium
Sorry to burst the collective “WHAT” bubble, but, although these “light organs” have not been investigated since the early 20th century, they are believed to simply reflect light, not produce it. That means they are likely not phosphorescent. But they definitely still fulfill the same role as they would had they indeed produced light. In conjunction with the “palate marked in the fashion of a domino” these unique features make sure that mom finds her mark when feeding her young. These odd characteristics are found in several species of Australian cavity-nesting finches. (McAtee, W. L. 1947. Luminosity in Birds. American Midland Naturalist, 207-213).