Hybridization between these species is remarkable across vertebrate species, as such events typically occur between recently diverged populations, whereas the most recent common ancestor to blue (Cyanocitta cristata) and green (Cyanocorax yncas) jays is estimated to have lived at least 7 million years ago.
A male hybrid of a green jay mother and a blue jay father. Image credit: Brian R. Stokes.
“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 graduate student at the University of Texas at Austin.
“Past vertebrate hybrids have resulted from human activity, like the introduction of invasive species, or the recent expansion of one species’ range into another’s, but this case appears to have occurred when shifts in weather patterns spurred the expansion of both parent species.”
In the 1950s, the ranges of green jays, a tropical bird found across Central America, extended just barely up from Mexico into south Texas and the range of blue jays, a temperate bird living all across the Eastern U.S., only extended about as far west as Houston. They almost never came into contact with each other.
But since then, as green jays have pushed north and blue jays have pushed west, their ranges have converged around San Antonio.
As a Ph.D. candidate studying green jays in Texas, Stokes was in the habit of monitoring several social media sites where birders share photos of their sightings. It was one of several ways he located birds to trap, take blood samples for genetic analysis and release unharmed back to the wild.
One day, he saw a grainy photo of an odd-looking blue bird with a black mask and white chest posted by a woman in a suburb northeast of San Antonio. It was vaguely like a blue jay, but clearly different. The backyard birder invited Stokes to her house to see it firsthand.
“The first day, we tried to catch it, but it was really uncooperative,” Stokes said.
“But the second day, we got lucky.”
The bird got tangled in a mist net, basically a long rectangular mesh of black nylon threads stretched between two poles that is easy for a flying bird to overlook as it’s soaring through the air, focused on some destination beyond.
Stokes caught and released dozens of other birds, before his quarry finally blundered into his net on the second day.
He took a quick blood sample of this strange bird, banded its leg to help relocate it in the future, and then let it go.
Interestingly, the bird disappeared for a few years and then returned to the woman’s yard in June 2025. It’s not clear what was so special about her yard.
“I don’t know what it was, but it was kind of like random happenstance,” Stokes said.
“If it had gone two houses down, probably it would have never been reported anywhere.”
According to the study, the bird is a male hybrid offspring of a green jay mother and a blue jay father.
That makes it like another hybrid that researchers in the 1970s brought into being by crossing a green jay and a blue jay in captivity.
“Hybridization is probably way more common in the natural world than researchers know about because there’s just so much inability to report these things happening,” Stokes said.
“And it’s probably possible in a lot of species that we just don’t see because they’re physically separated from one another and so they don’t get the chance to try to mate.”
The team’s paper was published in the journal Ecology and Evolution.
_____
Brian R. Stokes & Timothy H. Keitt. 2025. An Intergeneric Hybrid between Historically Isolated Temperate and Tropical Jays Following Recent Range Expansion. Ecology and Evolution 15 (9): e72148; doi: 10.1002/ece3.72148
