Rosa Rubicondior: Creationism Refuted - Evolutionary Divergence and A Hybrid Jay

Friday, 19 September 2025

Creationism Refuted - Evolutionary Divergence and A Hybrid Jay

A grue jay? Rare hybrid bird identified in Texas

(a) Blue Jay by Travis Maher (ML578309451). Cornell Lab of Ornithology, Macaulay Library.

(b) Hybrid Jay by Brian R. Stokes.

An interesting example of hybridisation between two distantly related species of jay has been reported by two biologists at the University of Texas, Austin. The hybrid is a cross between a blue jay (Cyanocitta cristata) and a green jay (Cyanocorax yncas). Although both are jays — members of the crow (Corvid) family — these two belong to different genera that diverged some seven million years ago and, until recently, lived in non-overlapping ranges in North America. Climate change has allowed them to extend their ranges, bringing them into contact only within the past decade.

The reason this is scientifically significant is that it illustrates how divergent evolution proceeds, and why it does not always progress to complete reproductive isolation. Unlike many other vertebrates, the genomic arrangements of birds are remarkably stable. As long as alleles remain in the same chromosomal loci, interbreeding remains possible. This can be disadvantageous if it results in hybrids with reduced fitness. For example, one population may evolve a long, slender bill adapted for one type of seed, while another evolves a short, stout bill for harder seeds. A hybrid might inherit an intermediate bill suited to neither, creating obvious disadvantages. In such cases, natural selection favours the evolution of barriers to hybridisation.

In many organisms, this is achieved by genetic rearrangements that prevent a zygote from developing even when mating occurs—so-called post-zygotic barriers. Where genomes are stable, such rearrangements rarely arise, so species tend instead to evolve pre-zygotic barriers that prevent mating or fertilisation in the first place. Among birds, these often take the form of plumage differences, mating rituals, or song—hence their remarkable diversity.

For these barriers to evolve at all, diverging populations must remain in contact so that selection can act against hybrids. In the case of the blue jay and green jay, however, their ranges were separate until very recently. With little or no contact, there was no selective pressure to develop strong barriers beyond the initial pre-zygotic signals of plumage and behaviour. These differences may have arisen through drift or other selective pressures in their respective ranges, but because plumage is closely tied to reproduction, it is more likely that sexual selection drove their divergence.

Thus, these jays provide a neat illustration of evolutionary divergence that has not progressed to completion, and why the scientific concept of a “species” must remain flexible. Nature does not obey our taxonomic rules, and the boundaries between species are often blurred.

Such examples of hybridisation — common also in geese and ducks, as I discussed in my blog post, Evolution of a Strange Pair of Geese — pose a problem for creationists. They insist that all extant species were created fully formed 6,000–10,000 years ago by magic, or else diverged by some mysterious warp-speed evolution following a global genocidal flood which, equally mysteriously, came to a halt just before human history began to be recorded.

Although this may seem to be a problem for science in that it highlights the difficulty with precise taxonomic classification, it is actually what the Theory of Evolution, which describes a process over time and not the sudden event of creationist parodies, predicts. In reality, cases such as this provide some of the clearest evidence of evolutionary divergence from common ancestors over millions of years.

Evolutionary Divergence of Corvids and North American Jays.

The Corvid family (Corvidae) includes crows, ravens, magpies, and jays. It is one of the most widespread and successful bird families, with members on every continent except Antarctica.
Origins: Corvids are thought to have originated in Asia around 17 million years ago. From there they radiated into different lineages, adapting to varied environments.
Jays: Jays form several distinct genera within Corvidae. North America is especially rich in jay diversity, with species including:

Blue jay (Cyanocitta cristata) - widespread across eastern and central North America.
Steller’s jay (Cyanocitta stelleri) - western forests.
Green jay (Cyanocorax yncas) - southern Texas into Central and South America.
Florida scrub-jay (Aphelocoma coerulescens) - an endangered species restricted to Florida scrub habitats.
Woodhouse’s and California scrub-jays (Aphelocoma woodhouseii and A. californica) - western U.S. scrub and oak woodlands.
Mexican jay (Aphelocoma wollweberi) - southwestern U.S. and Mexico.

Divergence:

Genetic studies show that the Cyanocitta jays (blue and Steller’s) split from their relatives about 5–7 million years ago.
Cyanocorax (green jays and relatives) diverged earlier, around 7–8 million years ago, with most species found in Central and South America.
Aphelocoma jays (scrub-jays and Mexican jay) represent another distinct branch, diverging about 5 million years ago.

Why so diverse? Jays adapted to different habitats and food sources—forests, scrublands, savannahs—leading to divergence in plumage, behaviour, and ecology.
Overlap today: Historically, many of these species occupied separate ranges. Climate change and habitat alteration are now bringing them into contact, sometimes resulting in hybridisation events, as with the blue and green jay.

The discovery is described in detail, with a fascinating overview of many other instances of inter-generic hybrids, in an open-access paper in Ecology and Evolution. It is also summarised in a press release from the University of Texas at Austin, published in EurekAlert!.

So what should we call this – a grue jay?
The rare hybrid offspring of a blue jay and a green jay is likely a result of weather-related shifts in the range of the two species.
Biologists at The University of Texas at Austin, who have reported discovering a bird that’s the natural result of a green jay and a blue jay’s mating, say it may be among the first examples of a hybrid animal that exists because of recent changing patterns in the climate. The two different parent species are separated by 7 million years of evolution, and their ranges didn’t overlap as recently as a few decades ago.

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.

Brian R. Stokes, first author
Department of Integrative Biology
University of Texas at Austin
Austin, Texas, USA.

Stokes noted that 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 – think polar bears and grizzlies – 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, but the second day, we got lucky.

Brian R. Stokes.

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.

Stokes 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. If it had gone two houses down, probably it would have never been reported anywhere.

Brian R. Stokes.

According to an analysis by Stokes and his faculty advisor, integrative biology professor Tim Keitt, published in the journal Ecology and Evolution, 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. That taxidermically preserved bird looks much like the one Stokes and Keitt describe and is in the collections of the Fort Worth Museum of Science and History.
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. 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.

Brian R. Stokes.

The researchers did not opt to name the hybrid bird, but other naturally occurring hybrids have received nicknames like “grolar bear” for the polar bear-grizzly hybrid, “coywolf” for a creature that’s part coyote and part wolf and “narluga” for an animal with both narwhal and beluga whale parents.

Publication:
Stokes, B. R., and T. H. Keitt. 2025.
An Intergeneric Hybrid Between Historically Isolated Temperate and Tropical Jays Following Recent Range Expansion. Ecology and Evolution 15(9): e72148. https://doi.org/10.1002/ece3.72148.

An Intergeneric Hybrid Between Historically Isolated Temperate and Tropical Jays Following Recent Range Expansion
Brian R. Stokes, Timothy H. Keitt

ABSTRACT
Shifts in species' ranges are creating novel ecosystems and previously unobserved species interactions. Documenting and understanding these novel interactions between species is an emergent priority of global ecological importance. We report a wild hybridization resulting from recent range expansion: a hybrid between Green Jay (Cyanocorax yncas) and Blue Jay (Cyanocitta cristata), charismatic and historically allopatric species whose ranges newly overlap in Texas. Morphological and genetic evidence indicate the hybrid individual resulted from the pairing of a female Green Jay and a male Blue Jay. 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 and Green Jays is estimated to have lived at least 7 million years ago. We believe this hybridization event joins a growing list of increasingly unexpected outcomes of contemporaneous range expansions fueled by anthropogenic global change. As birds are keystone species in ecological webs and reservoirs for zoonotic diseases, the creation of unique genomic contexts resulting from climate-driven hybridization is a phenomenon of both scientific and practical importance.

1 Introduction
Global heating is causing the expansion of the tropical climate zone (Staten et al. 2018) and tropical species are increasingly expanding their ranges away from the equator (Chen et al. 2011; McCarty 2001). Concurrently, changes in land use and land cover are driving range expansions of disturbance-tolerant species affiliated with agricultural and suburban environments (Villarreal-Barajas and Martorell 2009; With 2002). These dynamics may increase the frequency of interaction between tropical and temperate species. Such interactions can foster the development of novel ecological communities—often referred to as “no-analog” communities—where species coexist in combinations that have not been previously observed (Williams and Jackson 2007). “Anthropogenic Hybridization” is one potential outcome of these no-analog communities, supported by a growing body of evidence in both published literature and non-peer reviewed reports (Larson et al. 2019; Parmesan 2006). Previous examples of anthropogenic hybridization have primarily focused on hybridization driven by human-assisted species introductions and habitat modification via disturbance or altered fire regimes (Grabenstein and Taylor 2018.1; Ottenburghs 2021), with relatively few examples addressing hybridization driven indirectly by climate change (Chunco 2014). Our current knowledge of ecology and evolutionary mechanics provides a limited capacity to predict future outcomes under complex no-analog conditions (Mouquet et al. 2015; Walther 2010) including the potential for novel hybridization between historically isolated species. Here, we report a previously undescribed case of hybridization in the wild between historically isolated tropical and temperate corvids facilitated by anthropogenic change.

To our knowledge, this is the first record of non-captive hybridization between a Green Jay (Cyanocorax yncas) and a Blue Jay (Cyanocitta cristata). The Green Jay is a tropical species distributed from the northern Andes through Central America and Mexico into southern Texas. Green Jays are found in a limited region of Texas, where uniquely iridescent green and blue plumage makes them unmistakable and highly sought after by bird watchers. Thus, their range is well documented by citizen science datasets, such as eBird (Sullivan et al. 2009.1). Concordant with other species distributed at the tropical margin, Green Jays have remarkably expanded their range over the past two decades, shifting as much as 2 degrees of latitude over the span of a few generations (Sauer et al. 2022). Although experimental evidence of the role of climate change is lacking for most species range shifts, the region is warming rapidly, and we hypothesize that the lack of prolonged periods of freezing winter temperatures has released this species from its historical range limit in deep southern Texas (Osland et al. 2021.1; Rappole et al. 2011.1, 2007.1). The Blue Jay has similarly expanded its range to south and west Texas during a similar time period (Engels and Sexton 1994; Hutchinson and Scalise 2019.1). While climate change may have played a role in the range expansion of the Blue Jay, we note that this species has tracked the expansion of human settlement in other regions and is common in suburban gardens. Both species are commonly observed at artificial feeding stations, and thus we cannot rule out potentially interacting influences of climate and food subsidies on range dynamics.

A remarkable attribute of this observation is that unlike the majority of avian hybridization events documented in the wild, the Green and the Blue Jay are relatively distantly related and are not classified within the same genus. Phylogenetic analyses suggest that the ancestral lineages of these species diverged during the late Miocene, ~7.5 MYA (McCullough et al. 2022.1). Hybridization is relatively common among bird species (Grant and Grant 1992; McCarthy 2006.1), with approximately 16% of all bird species reported to hybridize in the wild (Ottenburghs et al. 2015.1), although this estimate is likely conservative due to underreporting. Most reported cases of hybridization rely on phenotypic observations, which can lead to substantial uncertainty when attempting to identify hybrids in the wild; thus, the use of genetic methodologies should be recognized as the gold standard for confirming hybrid identity and paternity (Ottenburghs 2021). Without genetic validation, even taxon experts can misidentify the paternity of hybrid specimens, as demonstrated by Alfieri et al. (2023).

The most phylogenetically divergent avian hybrid confirmed by genetic analysis is between the Gallus gallus (Domestic chicken) and Numida meleagris (Helmeted guineafowl), species which diverged ~51 to 65 MYA (Alfieri et al. 2024, 2023). An equally divergent hybrid of N. meleagris × Pavo cristatus (Indian peafowl) has also been described, but not confirmed through genetic analysis (Hanebrink et al. 1973). Non-domestic species have also been observed to produce hybrids in captivity between highly divergent pairs, including a recorded cross between Cardinalis cardinalis (Northern Cardinal) × Paroaria coronate (Red-crested cardinal) which diverged ~38 MYA (McCarthy 2006.1).

Instances of wild hybridization have been extensively recorded within the family Corvidae (McCarthy 2006.1; Ottenburghs et al. 2015.1). Corvidae includes 138 species with an estimated crown group divergence of ~10.8 MYA, according to phylogenetic analysis from McCullough et al. (2022.1). New World jays comprise a monophyletic grouping within Corvidae of ~38 species which diverged ~8.3 MYA (McCullough et al. 2022.1) and include the genera Aphelocoma, Gymnorhinus, Cyanocitta, Calocitta, Cyanocorax, and Cyanolyca. We identified reports of 26 intrageneric hybrids (crosses within the same genus) and 0 intergeneric hybrids (crosses between different genera) among Corvidae species outside the New World jay clade. Within the New World jays, we found 11 reports of intrageneric hybrids and two of intergeneric hybrids. Notably, there were no reports of crosses between New World jay species and other members of Corvidae. The two intergeneric hybridizations are Aphelocoma californica (California Scrub Jay) × Cyanocitta stelleri (Stellers Jay) and Cyanocitta cristata (Blue Jay) × Aphelocoma coerulescens (Florida Scrub-jay) (Morgan and Morgan 1997). Both pairs diverged ~6.8 MYA (McCullough et al. 2022.1).

Previously, no C. yncas hybrids had been reported in the wild, but a hybrid C. yncas × C. cristata was produced in captivity in 1965 at the Zoological Park in Fort Worth, Texas (Pulich and Dellinger 1981). In the publication describing this hybrid the authors wrote “The possibility of the Green Jay and the Blue Jay occurring naturally together during the breeding season is remote, so that hybrids are not to be expected in the wild.” At the time of Pulich and Delliger's publication Green and Blue Jay breeding ranges would have been separated by about 200 km (Sauer et al. 2022). Here, we use genomic data to confirm the identity of the hybrid's parent species and to compare patterns of heterozygosity with other New World jay species. Additionally, we make use of citizen science and climate datasets to describe potential future range change and overlap between these species based on results from ecological niche models.

Stokes, B. R., and T. H. Keitt. 2025.
An Intergeneric Hybrid Between Historically Isolated Temperate and Tropical Jays Following Recent Range Expansion. Ecology and Evolution 15(9): e72148. https://doi.org/10.1002/ece3.72148.

Copyright: © 2025 The authors.
Published by John Wiley & Sons, Inc. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

Hybridisation between such distantly related species as the blue jay and the green jay serves as a timely reminder that evolution is a process, not an event. The boundaries we draw between species are human attempts to categorise nature’s complexity, but nature itself rarely presents us with neat divisions. Instead, we often find gradients, overlaps, and exceptions that illustrate both the fluidity of evolutionary change and the resilience of life’s genetic toolkit.

Far from being an embarrassment to evolutionary biology, these hybrids are exactly what we would expect if species have diverged gradually from common ancestors, with reproductive barriers evolving at different rates. Where the genomic architecture remains stable, as in birds, hybridisation can persist even across millions of years of separation. What matters is not whether hybridisation occurs, but how natural selection acts on these crosses—sometimes reinforcing divergence, sometimes producing novel combinations, and sometimes revealing just how recent or incomplete that divergence has been.

For creationists, however, such examples are deeply problematic. They show that “kinds” are not immutable categories created in their present form, but dynamic populations connected by shared ancestry and continuous evolutionary history. The fossil record, molecular data, and living hybrids together paint a consistent picture of life’s descent with modification over vast timescales. Hybrid jays are not anomalies to be dismissed; they are evidence of the very processes that creationist dogma denies.

In short, these birds are not only a curiosity of ornithology but also a vivid demonstration of how evolution works in practice—messy, gradual, and ongoing. The hybrid jays remind us that life is always in flux, that species boundaries are porous, and that evolution’s creative power has been shaping, and continues to shape, the living world around us.

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