Biologists have caught an extremely unusual bird in Pennsylvania’s woodlands that is genetically part male and part female, divided down the middle and displaying the vibrantly colored traits of both sexes.
According to a release from the Carnegie Museum of Natural History, researchers caught and banded the rare bird on September 24 at the Powdermill Nature Reserve in Rector, Pennsylvania.
The rose-breasted grosbeak (Pheucticus ludovicianus) is a big seed-eating member of the cardinal family that can be found across much of eastern North America.
The male of this species is recognized for its vibrant plumage, but this specimen has particularly unique colored feathers on each side of its body: the right side is rosy red like a male, while the left side is brown-orange like a female.
This is due to the animal’s unusual case of bilateral gynandromorphism, which occurs when an animal’s external appearance is split in half by sex, half-male and half-female.
“The entire banding team was very excited to see such a rarity up close, and are riding the high of this once-in-a-lifetime experience. One of them described it as ‘seeing a unicorn’ and another described the adrenaline rush of seeing something so remarkable,” Annie Lindsay, Powdermill’s bird banding program manager, added.
“Bilateral gynandromorphism, while very uncommon, is normal and provides an excellent example of a fascinating genetic process that few people ever encounter.”
You’re probably wondering how this unusual phenomenon occurs.
First and foremost, sex determination in birds differs slightly from that in humans. Females have two copies of the same sex chromosome (XX) and men have one copy of each (XY) in humans, but in birds, it’s the other way around.
Males have two sex chromosomes (ZZ), while females only have one of each (ZW).
Gynandromorphy is supposed to happen for a variety of causes in different species, but it’s thought to happen in birds when an egg hatches with two nuclei, one with a Z and the other with a W.
The egg develops with both ZZ (male) and ZW (female) chromosomes if fertilized by sperm bearing two male Z chromosomes.
The researchers who found this new gynandromorph bird are now eager to see if it can reproduce successfully.
Because only the left ovary is generally functioning in birds, and this bird’s left side is the female side, the person might conceivably procreate with a male.
However, it’s possible that its distinctive feathers will elicit a territorial response from other males, reducing its chances of courtship.
Although the chances of developing gynandromorphy are extremely tiny, bilateral gynandromorphism has been observed in a variety of animals. In early 2019, a couple (also from Pennsylvania) noticed a northern cardinal (Cardinalis cardinalis) with half-brown and half-red gynandromorphy.
Earlier this year, scientists discovered a gynandromorph bee with a long antenna and smoother mandible on the male side, but a short antenna, spikey mandible, and bulky hind leg on the female side.