Bird-watchers, nature lovers, amateur photographers spend ages spying on wildlife in the hope of seeing, perhaps even capturing on camera, a rare and wondrous sight. A couple from Pennsylvania just got that experience when they noticed a very peculiar bird hanging out in their garden.
One side of the bird, a northern cardinal (Cardinalis cardinalis), had the spectacular scarlet plumage of the male, and the other half, the soft brown-green of the female – split exactly in the middle. Wow.
“Never did we ever think we would see something like this in all the years we’ve been [bird] feeding,” Shirley Caldwell told National Geographic about the bird she and her husband Jeffrey spotted in their garden in Erie, Pennsylvania.
When the bird had turned up again and again for weeks, Shirley snapped a photo of it while it was chilling in a dawn redwood tree just 9 meters (30 feet) from their kitchen window. Gotcha. A perfect shot of a half-male, half-female cardinal bird.
But wait. Half-male, half-female? Yes, indeed. The rarely occurring phenomenon is called bilateral gynandromorphism, whereby the external appearance of a species member is split down the middle, with one part being male, the other one female. It has been seen in a variety of organisms, including birds, insects, and crustaceans.
In fact, the phenomenon probably occurs more often than we would reckon, as we only tend to notice it when it’s really obvious. Like in a species that is sexually dimorphic – meaning there are explicit differences in the appearance of adult males and females.
Basically, sex determination in birds is the opposite of humans. Human females have two copies of the same sex chromosome (XX) and the male having a copy of each (XY). In birds it’s the other way around. Bird chromosomes are Z and W, so the female has ZW and the male has ZZ. This means males’ sperm only carries Z, while females produce eggs with either Z or W.
Gynandromorphy occurs differently in different species. In birds, it’s thought to happen when an egg develops with two nuclei, one carrying a Z, the other a W. If it gets fertilized by two ZZ sperm, then the embryo will carry both ZW and ZZ cells.
But can gynandromorphic birds themselves breed?
According to Dr Alex Bond, senior curator in charge of birds at the Natural History Museum, they probably can. However, it may not be an easy feat.
“If the gynandromorphy is complete, then birds will have one ovary and one testis. But all birds have just one urogenital opening – the cloaca. So externally they would look the same.”
However, “If the breeding involves sex-specific behaviors, like songs or courtship dances, though, these may be only partial or modified, meaning the bird won’t be as attractive to the partner it’s trying to woo.”
Back in 2014, researchers studied another bilateral gynandromorphic northern cardinal for over a month and observed that it never paired up, or sang. It’s possible its behavior, rather than its looks, confused other cardinals.
“Much like some hybrids exhibit behaviors from both species, gynandromorphs combine aspects of behavior from both sexes,” Dr Bond explained. “In some cases, they may sing like a male, but have the courtship dance of a female. Or the song and/or behavior may only be partial.”
This means it may not be so easy for these unique cardinals to find love, but Shirley remains positive. She revealed it has been spotted a few times in the company of a male.
“We’re happy it’s not lonely,” she said. “Who knows, maybe we will be lucky enough to see a family in summer!”