The first known naturally iridescent eggs have just been identified and are laid by a bird known as the great tinamou, aka “mountain hen,” according to a paper published in the latest issue of the Journal of the Royal Society Interface.
Great tinamou eggs are so luminous that viewers actually perceive them as changing color when they are seen from different angles.
“Tinamous have some of the most colorful and glossy eggs of all birds, and here we show that an extremely smooth eggshell cuticle produces their mirror-like sheen,” Branislav Igic, lead author of the paper, and colleagues wrote. “Furthermore, we reveal the presence of iridescence on the blue eggs of the great tinamou, an optical effect that has not been previously reported for avian eggs.”
Great tinamous, native to Central and South America, are about the size and shape of a small turkey. Their body coloration is a bit drab (with colors ranging from olive green to white), but they help the bird to stay well camouflaged in their rainforest habitat.
Charles Darwin himself treasured a tinamou egg from a different species. The egg was found after Darwin’s death in his collections. At some point during his lifetime, Darwin accidentally cracked the egg, but the still-shiny specimen went on display earlier this year.
For the new study, Igic, a researcher from the University of Akron’s Department of Biology and Integrated Bioscience Program, and the other researchers used chemical analysis and a barrage of high-powered magnifying devices to study tinamou eggs.
They determined that an extremely smooth cuticle produces the glossy appearance of tinamou eggshells. The cuticle is composed of calcium carbonate, calcium phosphate and, potentially, organic compounds such as proteins and pigments.