Why is the Inca Jay not a Green Jay?

While birding the east slope of the Andes in Ecuador one bird that was relatively common was the Inca Jay, a bird that was until recently considered merely an interesting population of Green Jays by all of the listing authorities.  But in 2009, the International Ornithological Congress* split the Inca Jay Cyanocorax yncas from the Green Jay, which was renamed Cyanocorax luxuosus.  Though many field ornithologists had apparently long considered the two birds separate species based on differences in appearance, behavior, vocalizations, and their disjunct range, the scientific evidence is not terribly developed.  In fact, the IOC decision to split the species is backed up by “The distinctive Cyanocorax luxuosus of Middle America is split from C. yncas (Ridgely & Greenfield 2001; Hilty 2003); AOU may review. Note switch of Green Jay from C. yncas to C. luxuosus.”

The two citations might seem like an impressive display of evidence for the split but the works being referenced are field guides!  And while no one (least of all a lowly bird blogger) is going to question the credentials of Robert Ridgely and Paul Greenfield, who, after all, wrote and illustrated The Birds of Ecuador, the book I used on my recent trip, or Steve Hilty, who also has an impressive resume full of field guide writing, including the referenced Birds of Venezuela, field guides do not seem to me to have the scientific gravitas necessary to determine if a species should be split.  But it seems like that is what the IOC did here in 2009!

You might have noticed that the IOC referenced the fact that the “AOU may review.”  The “AOU” refers to the American Ornithologists Union and their South American Checklist Committee has taken no action despite recognizing that the two field guides already referenced have split Cyanocorax ynca.  Why has the committee taken no action?  No one has written up a proposal suggesting that the bird be split yet!**  Oddly, there is a reference in the footnotes of the checklist to the fact that previously the bird had been considered two species but had, at some point, been lumped, but no reference for why or when this happened is given.

Inca Jay Cyanocorax yncas

Now, for the record, I am certainly not saying that the species should be lumped by the IOC.  After all, I have seen both species and my life list, which I keep on the IOC checklist, would suffer if they were lumped!  And the two birds certainly look different as you can see from the pictures with which I have illustrated this post.  The few birders I have asked who have experience with both birds support the split too.  But beyond the obvious “They look different and live in different places” what actual scientific evidence supports the split?

Green Jay Cyanocorax luxuosus by Mike Bergin

Here is where the fact that I know birders who actually have a scientific background and are willing to look up interesting stuff comes in to play (Thanks, Shawn!).  Last year a paper entitled “Molecular systematics and evolution of the Cyanocorax jays” with Elisa Bonaccorso credited as the lead author was published in Molecular Phylogenics and Evolution.  In it is the answer I was seeking!

C. yncas sequences separated into distinct groups corresponding the disjunct North and South American portions of the range of the species.  Differences in plumage, habitat preferences, social behavior, and vocalizations suggest that these populations might represent distinct species…Further analysis of populations from across the range of the species, particularly in Central America and northern South America, will be crucial in assessing their validity as independent evolutionary lineages.***

So, while it is couched with caution and tempered by a need for more data, as is only suitable for a scientific publication, it is pretty clear to me that this is a pretty darn big step towards solid scientific evidence that we have two different species.  After all if they look different, act different, prefer different habitat, sound different, and have different DNA then one would think that they are different species.  But, as Nick Sly pointed out to me in an email:

I think it’s simply a matter of taste – they look different, they have separate ranges, and they are genetically distinct (although they are sister species). Without being able to test hybridization because of their separate ranges, there is really no more evidence you can bring to bear on it. Some people like to split, some don’t.

What is the ultimate lesson to be learned here?  For me it is that though theoretically there  is a definition of what a species is, in practice that definition can be somewhat mutable and open to interpretation.  Biology is messy and when it comes to taxonomy the well-ordered and clean checklists can hide a whole heaping mess just beneath the surface.  All I was looking for when I started this post was a clear, concise, explanation as to why and when the gorgeous and gregarious jays I saw in Ecuador were considered a different species from the jays I saw in Honduras.  As you can see, no such explanation is available but I have been fascinated by what I did find.

Inca Jay Cyanocorax yncas eating a moth

*Which has itself changed its name to International Ornithologist’s Union.  Despite the name change they, and everyone else, still refer to their checklist as the “IOC list.”  If the list-makers can’t even keep their own name straight how can they get the birds right?

**Interesting, but ultimately irrelevant is the fact that the same document that is linked let me know that Cyanocorax ynca was, until 1953, in a monotypic genus and was considered Xanthoura ynca.

***I removed footnotes from the quote to increase its readability.  Each and every difference mentioned is backed up by a footnote in the original.

Inca Jay Cyanocorax yncas

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