There was something strange about the turquoise-colored songbird flying around San Antonio in 2023. With its black-and-white tail bands and its jeering honk, it somewhat resembled and sounded like a blue jay. But it had the face and low, two-tone rattling call of a green jay.

The bird turned out to be an extremely rare hybrid that some are calling a “grue jay.” Genetic testing showed the hybrid bird had a green jay mother and a blue jay father, scientists report September 10 in Ecology and Evolution.

Though bird hybrids are not uncommon, a pairing between these two jays is remarkable as their ranges only recently began to overlap due to human activity, says Timothy Keitt, an ecologist and evolutionary biologist at the University of Texas at Austin.

The green jay (Cyanocorax yncas) is a tropical bird. At the turn of this century, the only place they lived within the United States was the Rio Grande Valley near the Texas–Mexico border. The bird’s range extends throughout Mexico and Central America, spanning as far south as Honduras. However, due to the warming climate, green jays have spread north by hundreds of kilometers and several degrees in latitude.

“And it happened quite quickly, maybe a 20-year-period,” Keitt says.

At the same time, the range of the blue jay (Cyanocitta cristata) is reaching farther west across Canada and the United States, including into south central Texas. Ecologists suggest blue jays are following humans into new areas, seeking rich food sources in suburban environments.

Hybridization in the wild usually occurs between species that share a recent common ancestor. However, the evolutionary split between blue jays and green jays was at least 7 million years ago during the late Miocene Epoch. (The last common ancestor of humans and chimpanzees also lived around this time.)

The fact that two organisms, which have been evolving independently, came together to produce a viable offspring after 7 million years is amazing, says Jamie Alfieri, an evolutionary biologist who researches speciation at the University of Iowa in Iowa City.

“It’s just a really long time. I mean, I don’t know how else to say that. It’s a really big number,” says Alfieri, who was not involved in Keitt’s study.

Why a green jay crossed the species divide to mate with a blue jay is a mystery. It could have been that both birds were attracted to novelty. Keitt says there have been instances where a new song type has been preferred among birds looking for mates. For example, researchers at the University of Lancaster found that a male blue tit is more likely to hold a female’s attention if he sings a unique song.

Another hypothesis is that both birds were at the far edges of their ranges. Unable to find a mate among their own species, pairing up was a sort of last-ditch effort.

Both strategies are a risk: Hybrids are sometimes sterile, though with birds, hybrid males are more likely to be able to reproduce than females. The spotted grue jay is male, so it’s possible that it will have offspring.

But while both blue and green jays are highly social, the grue jay appeared to be on its own. Perhaps the other blue jays that were in the area recognized that it was different and wouldn’t accept it into their group.

While Keitt doubts that blue and green jays will merge into a new species, this hybrid highlights the unusual and rapid ecological changes occurring due to human activity.

“So buckle in, folks,” he says. “We’re going to see very different outcomes,” lots of unusual weather and mixes of plants and animals we’ve never seen in the past.