Gender Through Rose-coloured Glasses

This bird discovered in the woodlands of Pennsylvania is an example of a bird with two genders, a creature so rare that it is like “seeing a unicorn”.

This is a rose-breasted grosbeak, a North American songbird that is commonly found in the woodland forests of Pennsylvania. While there are potentially hundreds of thousands of rose-breasted grosbeaks living in the wild, this particular bird is a one-in-a million.

And that is because it is both male and female. Researchers at the Powdermill Avian Research Centre in Pennsylvania tagged the creature a few weeks ago and were incredulous when they examined the bird and its plumage.

“The rose coloured feathers on the right side of the bird indicate that it is a male, but the yellow plumage on the left side indicates that it is also a female,” says Annie Lindsay, lead researcher at the Powdermill Avian Research Centre. “That means that this bird is a hybrid, an extremely rare example of a bilateral gynandromorph, which is a creature that has the physical attributes of both genders. One of the team that found it said coming across something like this is like seeing a unicorn.”

With the rare bird banded, Annie and her fellow researchers hope to keep an eye on how its life unfolds.

She says said the research team is eager to learn from this finding.

“They all are incredibly grateful to be part of such a noteworthy and interesting banding record,” Annie says. “Bilateral gynandromorphism, while very uncommon, is normal and provides an excellent example of a fascinating genetic process that few people ever encounter.”

Usually, these birds are sexually dimorphic, meaning the males and females have identifiable traits that distinguish them.

It has the male pink “wing pits,” breast spot and black wing feathers on the right side and the female yellow wing pits and browner wing on the left side.

In 64 years of banding birds at the nature reserve, avian researchers have recorded fewer than 10 bilateral gynandromorphs.

“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,” says Annie.

In mammals, males carry an X and Y chromosome, and females carry two X chromosomes. Those roles are switched in birds. Males carry two Z chromosomes and females carry a W and a Z chromosome. 

Scientists have debated whether bilateral gynandromorphs can breed, since only the left ovary is functional in birds.

With the rare bird now banded, its finders hope to keep an eye on how its life unfolds. Annie Lindsay says the research team is eager to learn from this finding.

“They all are incredibly grateful to be part of such a noteworthy and interesting banding record,” Lindsay said. “Bilateral gynandromorphism, while very uncommon, is normal and provides an excellent example of a fascinating genetic process that few people ever encounter.”