Rare Half-Male, Half-Female Cardinal Appears to Have Male Companion

A half-male, half-female cardinal has caught the attention of bird-watchers, National Geographic, and a potential male companion.

Avid backyard bird-watchers Jeffrey and Shirley Caldwell told National Geographic that in 25 years of tending a bird feeder, they've never seen anything like the half-male, half-female cardinal that now resides on their Erie, Pa., property.

The bird -- whose coloring splits down the middle of its body-- first arrived at the Caldwells' a few weeks ago. Its left side corresponds with the female cardinal color, taupe, and its right-side corresponds with the male cardinal color, vermilion.

Animals that are half-male and half-female are a phenomenon known as bilateral gynandromorphs. The chimeric effect occurs when a female egg develops with two nuclei --one that codes for male genes (Z) and one that codes for female genes (W). If both nuclei become fertilized by male sperm cells, the bird will develop with two distinct genders, according to National Geographic.

Daniel Hooper, a postdoctoral fellow at the Cornell Lab of Ornithology told the publication that while the phenomenon is likely to occur in all species of birds, it's only noticeable when the species' males and females have obvious differences from each other, otherwise 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 said.

While most bilateral gynandromorphs are infertile, Hooper said he believes this particular cardinal may be an exception: "This one may actually be fertile as the left side is female, and only the left ovary in birds in functional."

Shirley Caldwell said that the red and taupe cardinal is always in the company of a male cardinal, which, according to National Geographic, may hint at a potential future family.

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