In one of the most exciting annual AOU Check-list Supplements since I started taking interest in them almost a decade ago, Western Scrub-Jay (Aphelocoma californica) has been split into two species: California Scrub-Jay (A. californica) and Woodhouse’s Scrub-Jay (A. woodhouseii). Being Scrub-Jays, my favorite group of birds, this is a really thrilling occasion.
(Note: Michael Retter does his usual fantastic job at the ABA Blog summarizing the Scrub-Jay split along with the remainder of the taxonomic changes, some of which I hope to touch on soon. To see the actual supplement, click HERE. A worthwhile, if slightly foot-dragging, review on the three Western Scrub-Jay subspecies is advertised by Retter and can be found in the April 2016 issue of Birding).
The split of Western Scrub-Jay has been anticipated since 1995, when Florida Scrub-Jay (A. coerulescens) and Island Scrub-Jay (A. insularis) were split from Western. There was historical context for this anticipation, as from 1910-1931, the Western Scrub-Jay complex actually made up four species: California and Woodhouse’s Scrub-Jays, as well as the Blue-eared Scrub-Jay of Mexico (corresponding somewhat with Sumichrast’s Scrub-Jay, more below on that group) and the Texas Scrub-Jay.
In 2010, the initial proposal to split the species was rejected by the AOU Committee, with further research into genetic differences and hybridization needed. I recall this event as feeling fairly deflating, as even then, having only seen one Scrub-Jay, the genus Aphelocoma was nevertheless always in my thoughts as I longed for experience with its other members.
Following the rejection, further research by ornithologists (as cited in the aforementioned Birding article by Dessi Sieburth) “suggest[s] that Woodhouse’s and California Scrub-Jays are more different [genetically] than previously thought.” Prior to the 2010 decision, research had also shown that these two species “appear to be more genetically different from each other than are the Island and California Scrub-Jays,” which makes sense when considering the split and the likely way in which Island Scrub-Jay speciated.
Six years later, the first entry in this year’s initial batch of proposals detailed the recommendation to split the two groups, citing the genetic study mentioned in the preceding paragraph in addition to a second study done in 2014, which dealt with contact zones and reproductive isolation.
The one glaring omission from all of this seems to be a further split of Sumichrast’s Scrub-Jay (a genetically and morphologically distinct subspecies of Woodhouse’s Scrub-Jay from Central Mexico), which the authors of this year’s proposal address:
With respect to the sumichrasti group (sumichrasti + remota subspecies), Gowen et al. (2014) confirmed reciprocal monophyly of mtDNA with respect to other woodhouseii individuals. The divergence between sumichrasti and populations of central Mexico is greater than the divergence between insularis and californica (Fig.1 below). In microsatellites, individuals of sumichrasti and southern populations of woodhouseii were largely assigned to different genetic clusters (Fig. 3E; Gowen et al. 2014). However, Gowen et al. (2014) did not assess populations close to the putative area of contact near Mexico City (Pitelka 1951). Despite compelling evidence that the populations in southern Mexico constitute a distinct species, there is insufficient information regarding reproductive isolation to recommend splitting the sumichrasti group at this time.
It is unfortunate that justice cannot be taken now, but we should be looking for Sumichrast’s Scrub-Jay to be split from Woodhouse’s Scrub-Jay in the next decade, if not sooner.
A fascinating point made here is the fact that A. californica and A. insularis are more closely related than sumichrasti and woodhouseii. Like that made above regarding the closeness of California and Island Scrub-Jays versus California and Woodhouse’s, this discovery is unsurprising when considering geography. Much of the range of Sumichrast’s Scrub-Jay lies south of the Mexican Transvolvanic Belt, a major geographic barrier that acts as a mechanism for speciation. A related, though not completely congruent example, can even be found within Aphelocoma, with Mexican and Transvolvanic Jays (A. wollweberi and A. ultramarina, respectively): Mexican Jay is found north of the belt, Transvolcanic Jay is found along it (a fascinating overview of Scrub-Jay speciation, centering on Island, Florida, and ‘Western’ Scrub-Jays can be found in this Neotropical Birds Account).
So what is the significance of this split?
Scientifically, it does ornithological justice by clearing up an issue that has come to light with further genetic research: the fact that ‘Western’ Scrub-Jay is in fact paraphyletic. As the authors of the proposal note: “because californica and insularis are sister lineages, maintaining the status quo is inconsistent with the treatment of A. insularis as a full species (AOU 1995).”
Personally, the split provided me with my first armchair tick ever, a long-awaited accomplishment (I couldn’t think of a better species for it to happen with!). I first saw Woodhouse’s Scrub-Jay over a year before my first California (March 30, 2011 to July 26, 2012), but the likely specific differences between these two definitely crossed my mind when I laid eyes on my first Cali, adding significance to the sighting. My initial encounter with that species took place while driving from San Francisco Airport to Point Reyes National Seashore on the first day of my and my dad’s epic 2012 California adventure. I glimpsed the bird on the side of the road as we drove by (we saw more during the trip), an unfortunate occasion for a first look, as the exact location of roadside sightings is often next to impossible to track down. Luckily for me though, the bird was along a memorably beautiful stretch of road, and a little ‘scouting’ on Google Maps Street View last night appeared to pick up on that original location.
Birding-wise, we will have to learn to get used to two new names, but the benefit of that is that it keeps the name ‘Western Scrub-Jay’ reserved for discussions of the species complex as a whole (i.e. the “Sage Sparrow Complex”). Initially, a lot of us (myself included) will likely slip up and reflexively call an individual by the former name, but in the vast majority of cases, the birder will be easily understood based on geography alone.
I find it wonderfully fortuitous that I was able to put this website together just in time to cover this split, likely one of the two last species-level changes in this seemingly straightforward yet phylogenetically complex group. There is still much to be learned about these birds, especially those south of our border, such as Sumichrast’s Scrub-Jay, whose continued connection to Woodhouse’s is likely only due to this hole in our knowledge.
In addendum: for a good map of former Western Scrub-Jay subspecies, see the sixth edition of the National Geographic Field Guide to Birds of North America.
American Ornithologists’ Union [AOU]. 2016. Fifty-seventh Supplement to the American Ornithologists’ Union Check-list of North American Birds. The Auk. 2016. 133: 544-560.
The History of Bird Names in the American Ornithologists’ Union Checklists 1886-2000: Swifts through Creepers [Internet]. [2008 May 24, cited 2016 Jul 9] . Available from: http://darwiniana.org/zoo/AOUmenu.htm
American Ornithologists’ Union [AOU]. 2010. Fifty-first Supplement to the American Ornithologists’ Union Check-list of North American Birds. The Auk. 2010. 127(3): 726-744.
Sieburth, D. North America’s Scrub-Jays: How Many Species? Birding. 2016. 48(2):52-56.
McCormack, J., Maley, J., Cicero C. Elevate Aphelocoma californica woodhouseii to species rank. AOU Classification Committee – North and Middle America Proposal Set 2016-A. 2015. 1:2-6.