A blue jay and a green jay mated, researchers say. Their offspring is a scientific marvel

By Amanda Schupak

(CNN) — What do you get when you cross a blue jay with a green jay? That’s not the start of a joke, but the subject of a new study that aims to describe a hybrid bird never encountered before in the wild.

The bigger question scientists are puzzling over, though, is why does the mystery bird exist?

“We think it’s the first observed vertebrate that’s hybridized as a result of two species both expanding their ranges due, at least in part, to climate change,” said Brian Stokes, a doctoral student of biology at the University of Texas at Austin and first author of the study published September 10 in the journal Ecology and Evolution.

The vividly colored green jay is found in parts of South and Central America, Mexico and a limited portion of southern Texas. But since 2000, the tropical bird’s territory has expanded north by hundreds of kilometers — more than 100 miles and about 2 degrees of latitude — along the Rio Grande and up toward San Antonio, said study coauthor Timothy Keitt.

Avid birders across Central Texas have taken note, sharing sightings of the emerald birds on social media and apps like eBird. Keitt, a professor of integrative biology at UT Austin, has been keeping tabs on their rapid northward creep since 2018. “They’re pretty unmistakable in the field,” he told CNN. “You see a green jay and you absolutely know that it’s a green jay.”

Stokes joined Keitt’s project a few years later, trapping birds to take blood samples for genetic analysis and releasing them back into the wild. While monitoring social media for green jay sightings in May 2023, Stokes came across an intriguing post on a Facebook group called Texbirds. A woman in a suburb of San Antonio shared a photo of an unusual bird that didn’t look like any jay Stokes or Keitt had ever seen.

“He happened to notice that this person posted a picture of this odd jay, and immediately told me, and we got in the car and drove down to find it right away,” Keitt said.

He and Stokes described their finding as one of the “increasingly unexpected outcomes” that arise when global warming and land development converge to drive animal populations to new habitat ranges. This, they wrote, can lead to unpredictable animal interactions — in this case, between a tropical species and a temperate one — and create never-before-seen ecological communities.

Bird of a different feather in Texas

It took a couple tries to catch the suspected blue jay-green jay hybrid. Corvids — birds of a group that includes jays, crows and ravens — are notoriously clever.

The researchers tagged the mystery bird and drew blood for genetic sampling. They noted that their study subject displayed distinct traits of both blue and green jays — which aren’t that closely related and split off from a common ancestor around 7 million years ago.

The bird had blue feathers on its back and tail and white spots on its wings, similar to a blue jay. But it lacked a blue jay’s spiky crown and had a spot over its eye that is one telltale sign of a green jay. The outlier followed a flock of blue jays and made similar calls. But it also produced the clicks and rattling vocalizations of a green jay.

Upon returning to the lab, Keitt and Stokes completed a series of gene analyses, comparing the DNA they’d collected with that of a blue jay, a green jay and other jay species, and determined the mystery bird was the offspring of a male blue jay and a female green jay.

One other known example of a blue jay–green jay hybrid was born in captivity in the 1960s, when the two species’ natural breeding grounds would have been separated by some 200 kilometers (120 miles). The specimen is preserved in a museum collection in Texas and looks strikingly similar to the wild bird the researchers identified.

A blue jay–green jay pairing is a ‘biological curveball’

Gavin M. Leighton, an associate professor of biology at Buffalo State University in Western New York who has researched trends in hybridization among wild birds and was not involved in the study, was a little surprised by the pairing. Scientists, he said, tend to assume that hybridization arises from a case of mistaken identity — two birds that don’t realize they are mating with a member of a different species. Lots of hybrids among other types of birds exist, but many are more closely related than these jays.

To Leighton, the odd pairing is something of a “biological curveball.”

“Both of these jay species form long-term social bonds with a mate,” he explained. “We would expect them to be pretty choosy about who they form these pair bonds with.” What’s more, corvids are extremely smart, and blue jays and green jays look quite different from one another. They should have no problem telling themselves apart.

Perhaps, Leighton speculated, it was the end of breeding season and the birds were under pressure. “If they aren’t having good luck finding an individual in their own species that is also without a mate, then maybe there’s a higher risk of making a mistake,” he said.

Expanding territories as temperatures rise

It’s a mistake that could only have been made today, as it’s been just within the past 10 years that the blue jay’s and the green jay’s ranges have started to overlap. Blue jays, which are found all over the eastern United States, have been pushing westward, possibly following suburbanization and taking advantage of backyard bird feeders.

Meanwhile, recent increases in overnight temperatures in Texas may have made the region more hospitable to tropical species, which could explain green jays’ expansion north, according to Keitt. (They are frequent feeder visitors, too.) The two ranges converge around San Antonio — where the surprising hybrid was found.

“Species that may not have interacted for millions of years are suddenly coming into contact, and we believe that’s most likely as a result of anthropogenic factors, like climate change and habitat modification,” Keitt said.

He’s interested to see what happens if blue and green jays increasingly share the same habitat. Will they fight each other off? Or ignore each other and peacefully coexist? One thing is likely: They’ll probably get better at knowing who’s who.

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Amanda Schupak is a science and health journalist in New York City.