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Rare "Split" Cardinal Makes Birdwatchers Stop And Stare

Shirley Caldwell

Now here’s something you don’t see every day.

Birdwatchers who live in the eastern half of the country can easily recognize cardinals. The males are bright red all over, with matching beaks and feathered crests, while the females have the same shape but a tawny coat.

But what does that make this striking bird with red feathers on one side and brown feathers on the other? Interesting, to say the least.

The rare specimen was photographed in Erie, Pennsylvania by birdwatcher Shirley Caldwell, and has been spreading across the internet ever since.

The longtime birder told National Geographic that she and her husband Jeffrey were stunned when the cardinal first appeared in their backyard 10 weeks ago.

"Never did we ever think we would see something like this in all the years we've been feeding," she said.

The cardinal’s pied coat actually shows off its dual nature. The bird is a bilateral gynandromorph, or a animal whose body is half male and half female.

Half-sided cardinal
Half-sided cardinals are easier to spot than other birds born the same way.Brian Peer - Western Illinois University

These rare creatures, sometimes called "half-siders," are considered rare but not uncommon. One scientist guessed the number of birds born this way could be anywhere from 1 in 10,000 to 1 in 1,000,000.

All species of birds can probably be born half-sided, but it’s only noticeable with varieties like cardinals, where the coats are so different between males and females.

The science behind the split (feel free to skip this part if science puts you to sleep) has to do with the nature of bird chromosomes.

Birds have Z and W chromosomes, as females carry ZW while males have ZZ. When a bird’s egg develops both a Z and a W nuclei, and they’re both fertilized with Z chromosomes from the male bird, the result is a "chimera" or split animal.

Half-sided lobster
Pinchy, the half-sided lobster.New England Aquarium

The bird is split neatly down the middle, and studying the cells on either side would reveal they’re completely different.

Along with birds, crustaceans like lobsters and insects can also be born half-sided.

Even though half-sided birds are not so rare, there’s reason to be excited about this cardinal in particular.

Most gynandromorphs can’t breed, because their male side is on the left with the bird’s only functional ovary. That’s not the case with this bird, so there’s a chance it could actually start a family.

That would be truly unusual, since half-sided birds seem to either be shy or ostracized by either birds. Other half-sided cardinals observed by researchers never sang or paired up with other birds.

[H/T: National Geographic, IFL Science, BBC]

Have you ever seen a half-sided bird in real life?

I write about all sorts of things for Shared, especially weird facts, celebrity news, and viral stories. CONTACT: zachary@shared.com