Pennsylvania birdwatcher Shirley Caldwell spotted something unusual in her backyard this winter, a cardinal that appeared to be half-male (vermilion), and half-female (taupe), which was confirmed by an ornithologist to be a genuine bilateral gynandromorph (half-male, half-female). Caldwell's photos have since gone viral.
National Geographic reports: ‘Gynandromorphs, known as “half-siders” among ornithologists, are uncommon but not unheard of. They likely occur across all species of birds, Hooper says, but we're only likely to notice them in species where the adult males and females look distinct from each other, a trait known as sexual dimorphism. “Cardinals are one of the most well-known sexually dimorphic birds in North America—their bright red plumage in males is iconic—so people easily notice when they look different,” Hooper says.'
Caldwell's cardinal, which may be able to reproduce because it's ‘female' side is on the left “and only the left ovary in birds in functional” is always with a male. “We're happy it's not lonely,” she told NatGeo.