There is a Northern Cardinal visiting a backyard feeder in Erie, Pennsylvania that looks like a male on its left side (red plumage) but resembles a female cardinal on its right side (gray plumage). The bird is called a gynandromorph– an organism that contains both male and female characteristics. The term gynandromorph, from Greek γυνή (gynē) female, ἀνήρ (anēr) male, and μορφή (morphē) form, is mainly used in entomology, but it applies here. The cardinal never sang and appeared not to have a mate. Interestingly, about ten years previous to the sighting of this one, another gynandromorphic cardinal was spotted, but this one has the sexes reversed – red on the left and gray on the right.
It could be that two eggs of the female parent fused after fertilization and created a half and half bird, each side being the brother or sister of the other. Or it could be some genetic change. Humans have X and Y chromosomes. Males have XY and females XX. The Y chromosome has the genes that determine the formation of male characteristics and if there is no Y as in females, female characteristics appear. In birds, it is the opposite; they have Z and W chromosomes, ZZ for males and ZW for females. Something could have gone wrong with this system.
Gynandromorphism has never been seen in humans, but there are hermaphrodites. These are babies with the characteristics of both sexes, caused by a mutation. Sometimes the body leans one way and sometimes the other, and occasionally the person has two complete sets of genitals, a complete hermaphrodite.
In mammals and birds these sex abnormalities are rather rare but in lower creatures fairly common as a matter of course. The whiptail lizard only has the female sex; eggs develop via parthenogenesis – development without fertilization. That’s why they are sometimes called “lesbian lizards.” And reef fish are known to change sexes as they get bigger. When small they are females but as they get large enough to defend their territory, they become males. Female guppies, the common aquarium fish, do something similar.
Also check out National Geographic’s video of an ultra-rare “yellow cardinal” at an Alabama backyard feeder, along with an interesting and informative description of what happened genetically to create this male’s color anomaly. Ain’t life grand?