As It Happens

'Incredibly rare' male-female bird spotted at Pennsylvania nature reserve

Researchers at the Powdermill Nature Reserve in Pennsylvania were thrilled to be visited recently by a half male, half female rose-breasted grosbeak.

In more than 60 years of tagging birds, Powdermill Nature Reserve has only seen 5 gynandromorphs

This rose-breasted grosbeak is a gynandromorph, meaning it has both male and female sex characteristics. (Annie Lindsay/Powdermill Nature Reserve/Carnegie Museum of Natural History)

Researchers at the Powdermill Nature Reserve in Pennsylvania were thrilled to be visited recently by a half male, half female rose-breasted grosbeak.

Annie Lindsay, the bird banding program manager at the reserve in Rector, Pa., remembers getting the call on her walkie-talkie about the rare sighting and rushing to see it first-hand. 

Everyone was buzzing with excitement about the rare and beautiful creature, but had to keep their wits about them so they could follow their procedures of tagging it, taking measurements, and quickly releasing it back into the wild.

One researcher compared the fleeting moment to "'seeing a unicorn." Another described feeling an incredible adrenaline rush. 

"We only had it in the hand for a few minutes and then we released it," Lindsay told As It Happens host Carol Off. "It was incredibly rare to see this. So we were all very, very excited."

Pink for male, yellow for female 

The grosbeak is what's known in the scientific community as a gynandromorph — an organism that displays both male and female sex characteristics.

It's a rare, but not unheard of, phenomenon across the animal kingdom, appearing in birds, butterflies, crustaceans, and snakes, just to name a few. 

While it can present itself in a variety of ways, in this case, the bird likely has male and female chromosomes. 

"It happens when an egg — and I mean the cell, not the thing with the hard shell — they're supposed to get rid of about half the genetic material … and half that material is supposed to be packaged in something called a polar body that the egg expels," Lindsay said.

"In this case … it didn't happen that way. And so both the egg's nucleus and the polar body were fertilized."

The rose-breasted grosbeak is female on the left, and male on the right, with differences in both colouring and wing size. (Annie Lindsay/Powdermill Nature Reserve/Carnegie Museum of Natural History)

In Powdermill's 60-year history, they have recorded more than 800,000 birds. But they've only come across five gynandromorphs — at least, that they know of. 

"We would only be able to detect that if it's a species that the males and females look different," Lindsay said. "There are a lot of birds that we catch here that the males and females look the same, and so we wouldn't necessarily be able to detect that."

In the case of the rose-breasted grosbeak, males have a rose-red lining on the underside of their wings, while females sport a yellow colour. This particular bird had one of each.

"The pink side is genetically male, and that yellow side is genetically female," Lindsay said. 

Annie Lindsay is the bird banding program manager at Powdermill Nature Reserve in Rector, Pa. (Mary Shidel/Powdermill Nature Reserve/Carnegie Museum of Natural History)

Whether a gynandromorph can mate depends on a number of different factors. In this case, the researchers don't know enough about the bird to say for sure. 

But Lindsay suspects it's likely it could mate with male rose-breasted grosbeak, as its female side is where its ovary would be.

"So if this bird does have a functional left ovary, it's possible that it could find a male mate and reproduce that way," she said.

"There are some considerations, though. The bird would have to act like a female. Its behaviour would have to be female-like in order to attract a male mate. And so we don't know if that's how the bird behaves."

In 2019, As It Happens interviewed birdwatcher Shirley Caldwell, who captured photos of a gynandromorph cardinal in Erie, Pa., with colouring split right down the middle — bright red male on its right side and a muted yellowish brown female on the left.

That particular bird did appear to have a male paramour. 

"When the gynandromorph does leave, the male follows with it,"  Caldwell said at the time. "I always see them together."


Written by Sheena Goodyear. Interview produced by Lisa Bryn Rundle. 

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