It would be hard to determine this bird’s better half.

Last month, a couple of birdwatchers in Erie, Pa., had an interesting sighting at their feeder. It was a cardinal with a conundrum. Split right down the center, the cardinal had two distinct sides. On the left, the bird exhibited the bright red coloring of a male bird. However, the right side was the muted colors of the female bird. Was this a male or female?

The answer, perhaps surprisingly, is both. A rare condition called bilateral gynandromorphism results in a single animal that has both male and female sex organs and biological characteristics on opposing sides. These creatures have also been called half-siders.

The bird was not a hermaphrodite, which is an animal with both sexual reproductive structures, but other external characteristics defined by one sex or the other. Additionally, hermaphrodites are the natural condition for many species.

Though rare, gynandromorphy occurs with some frequency in birds, crustaceans, and insects. And it can occur bilaterally (left/right), polar (top/bottom), obliquely (on the diagonal), or as a mosaic.

In many cases, it isn’t as obvious as the cardinal, which has distinct appearances based on sex. Besides the cardinal, other obvious examples include grosbeaks, orioles, and even domestic chickens. The latter with gynandromorphy might be referred to as half-cocked. In animals that don’t exhibit sexual dimorphism, one might never know of this genetic variation without testing.

So how do these gynandromorphs behave? Like a male or female? The cardinal in question was not heard singing its male breeding song. Could it breed? Perhaps, since this bird’s left side was female, it is possible that it might be successful because many female birds have their only functioning ovary on the left side.

In studies, some of these birds have been found to be sterile, while others could breed. Time will tell, though sometimes in the cases of these gynandromorphs, they are shunned or bullied by others of their kind.

Gynandromophy is believed to occur in the first division of a zygote; mitosis gone bad, one could say. It is hypothesized that an occasional failure of cell division, either nondisjunction or chromosome loss, leaves the zygote with too few or too many chromosomes. If this happens early in cell division and with the chromosome that determines sex, gynandromorphy can occur.

Other studies show that bacterial or viral infections, temperature variations, hybridization and mutations can also be causative. Consider that after the Chernobyl and Fukushima nuclear disasters, an increase in gynandromorphy was observed.

Not surprisingly, gynandromorphy does not occur in mammals, which have a more complex reproductive process. A variety of other groups and categories exist in humans (intersex, genetic chimera, etc.), and these distinctions follow natural variations in species.

Only time will tell if the recently observed cardinal will get half a chance to be a parent. In this circumstance, there is no cardinal rule. No matter how it turns out, this gender-bending condition provides insight into the interplay of programming, chance, the perseverance of life, and the natural spectrum of gender.

Suzan Bellincampi is executive director of the Felix Neck Wildlife Sanctuary in Edgartown.