GRAND VALLEY, PA — When she saw the beautiful but peculiar-looking bird at her backyard feeder in Grand Valley, Annette Smith thought it was a genetic hybrid.
That sometimes happens in nature — not often, but it does happen.
A liger, for example, is a cross between a male lion and a female tiger, and it has a mix of both parents’ traits. A tigon is born when a male tiger and female lion mate. Typically, these hybrids are the result of breeding in captivity and are rare occurrences in nature.
But that wasn’t what the odd-looking warbler was, as longtime birder Jamie Hill learned, his curiosity piqued by Smith’s story.
“I wasn’t sure if she was referring to a hybrid, or a much rarer gynandromorphic bird” — that is, one that’s half male and half female, the Waterford man wrote on his Facebook page. “We immediately tracked down the homeowner by phone and were told it was a male Northern Cardinal that ‘had some white on its breast.’ ”
Well, Hill thought, maybe the bird had some albinistic feathering associated with leucism, a condition that can result in a partial loss of pigmentation in an animal. Smith texted a photo she’d taken, and Hill quickly ruled that out.
The Northern cardinal (Cardinalis cardinalis) was unlike any he had ever seen in 48 years of birding, and he called it a “once-in-a-lifetime, one in a million bird encounter!”
Males have flashy bright red plumage, while females are brownish with reddish tinges on their wings, tails and crests. This one had characteristics of both genders: its bright crimson feathers on one side suggested the bird was a male, but the subdued taupe feathers on the other were the plumage of a female.
“This bird would have a functioning ovary on its left side and a functioning single testis on its right,” Hill wrote, adding, “Theoretically, this bird could either mate with a normal male cardinal and lay fertile eggs, or it could mate with a normal female cardinal and father her eggs!”
Hill clicked off about 50 pictures of the rare bird before it flew away.
Jeffrey and Shirley Caldwell, of Erie, Pennsylvania, took photos of a half male, half female cardinal at their feeder in 2019. It was such a rarity the photos were picked up by National Geographic, The New York Times and multiple national birding magazines.
Hill said it’s possible the bird seen in Grand Valley is the same cardinal the Caldwells spotted in Erie in 2019. The two communities are about an hour apart as the, er, cardinal flies.
These birds, called “half-siders” among ornithologists, may be more common than anyone thinks, Daniel Hooper, a postdoctoral fellow at the Cornell Lab of Ornithology, told National Geographic. But it’s more noticeable in birds such as cardinals, where the differences between males and females are so striking, a trait known as sexual dimorphism, he said.
“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 told the magazine in 2019.
The half-sider Hooper saw didn’t sing, nor did the one observed in northwestern Illinois from December 2008 to March 2010.
In a paper published in the Wilson Journal of Ornithology, researchers Brian D. Peer and Robert W. Motz reported they observed a bilateral gynandromorph Northern cardinal for 40 days, mostly near bird feeders.
“It was never paired with another cardinal, was never heard vocalizing, and was not subjected to any unusual agonistic behaviors from other cardinals,” they wrote, describing their observations as “among the most extensive of any bilateral gynandromorph bird in the wild.”
But how does this happen?
Birds’ sex chromosomes are called Z and W. Females have a single copy of each (ZW) and males have two Z chromosomes (ZZ). Males produce sperm carrying the Z chromosome, and females produce eggs carrying either Z or W chromosomes.
“The predominant theory of how gynandromorphy occurs in birds is that an error occurs in the formation of an egg,” Carol A. Butler, a psychoanalyst with a specialty in sexual dysfunctions and gender dysphoria, wrote in Natural History magazine in 2017
“The egg normally carries one sex chromosome to unite with the single sex chromosome carried by the sperm,” she wrote, “but if an egg accidentally ends up with two chromosomes — a Z and a W — and if this aberrant egg is fertilized by two Z-carrying sperm, the bird that results will have some ZZ cells and some ZW cells, and it may have both male and female physical characteristics.”
Hooper said in the National Geographic interview that the cardinal he saw was “remarkable” and “a genuine male/female chimera.”
According to the magazine, the phenomenon also occurs in many insects and crustaceans.