The rare ‘grue jay’ may be a harbinger of environmental change

In a remarkable occurrence in 2023, residents in San Antonio witnessed an unusual turquoise-hued songbird flitting about, capturing the attention of birdwatchers and casual observers alike. The hybrid bird—displaying the striking black-and-white patterns on its tail reminiscent of a blue jay while making the distinctive two-tone rattling calls of a green jay—has garnered interest for its genetic background.

The avian phenomenon has been identified as an extremely rare hybrid that some ornithologists are referring to as a “grue jay.” Detailed genetic analyses completed on September 10 have revealed that the feathered hybrid sprang from a green jay mother paired with a blue jay father, as described in a study published in Ecology and Evolution.

While bird hybrids are not particularly rare, the emergence of a cross between these two distinct jay species is extraordinary. Their ranges only began to overlap recently, facilitated by human influences and environmental changes. Timothy Keitt, an ecologist and evolutionary biologist at the University of Texas at Austin, explains how anthropogenic factors have contributed to this unique pairing.

The green jay (Cyanocorax yncas) is primarily a tropical bird. Historically, its habitat in the United States was confined to the Rio Grande Valley near the Texas-Mexico border. Extending its reach further into the United States, the species has migrated hundreds of kilometers north and has adjusted its latitude by several degrees due to climate changes over the past couple of decades.

“This rapid range shift occurred fairly swiftly, within perhaps a 20-year period,” says Keitt.

Similarly, the blue jay (Cyanocitta cristata) has been extending its range westward across Canada and the United States, now reaching into southern regions of Texas. Ecologists attribute this phenomenon to blue jays following human settlements and exploiting the abundant food resources available in suburban areas.

Hybridization in the wild typically happens among species with shared genetic lineages. However, the divergence between blue jays and green jays extends back at least 7 million years to the late Miocene Epoch. It’s noteworthy to mention that the last common ancestor of humans and chimpanzees also existed around this time.

The fact that these two long-evolving species produced a viable hybrid offspring after such an extensive period is intriguing. Jamie Alfieri, an evolutionary biologist at the University of Iowa who did not partake in Keitt’s research, emphasizes the significance of this evolutionary milestone: “It’s just a really long time. I mean, I don’t know how else to say that. It’s a really big number.”

The motivations behind the green jay’s decision to mate with a blue jay remain unclear. One possibility is that both species were attracted to one another’s novelty. Keitt points out instances in the avian world where a unique song has significantly affected mate selection. Research conducted at the University of Lancaster highlighted that male blue tits were more successful in attracting females when singing distinctive melodies.

Another theory suggests that both the green and blue jays may have found themselves at the edges of their respective ranges, looking for companionship and having to mate across species lines as a last resort.

However, choosing a hybrid mate carries inherent risks, as hybrids can sometimes be sterile. In birds, while hybrid males often retain reproductive abilities, females have lesser odds. The spotted grue jay observed is male, which opens the possibility for potential offspring.

Despite the social nature of both blue and green jays, this unique hybrid appears solitary. It raises the question of whether its avian peers recognized its differences and rejected it from their social structures.

Though Keitt remains skeptical about the formation of a new species from these two jays, this hybrid serves as an emblem of the striking ecological transformations that human activities are catalyzing.

“So buckle in, folks,” he remarks, “We’re going to see many different outcomes, with unusual weather patterns and mixes of plants and animals that we’ve never observed in the past.”