Nuthatches are small, short-tailed, sharp-billed songbirds widely recognized for their ability to hitch headfirst down tree trunks and upside-down along limbs. The family has representatives throughout the forests North America, Eurasia (including North Africa), and Indomalaya. Nuthatches are related to the Wallcreeper, treecreepers (Certhiidae), gnatcatchers, and wrens.
In North America, we have, traditionally at least, four species, the most familiar of which is the White-breasted Nuthatch (Sitta carolinensis).
White-breasted Nuthatch photographed in Ontario by Matt MacGillivray
But two studies suggest that White-breasted Nuthatches actually represent four distinctive and largely isolated populations that may deserve full species status.
In 2007, Garth M. Spellman and John Klicka published a paper, Phylogeography of the white-breasted nuthatch (Sitta carolinensis): diversification in North American pine and oak woodlands (full-text PDF), in which they revealed the existence of four distinctive populations based on studies of a single gene. They identified the populations as follows: Eastern clade; Pacific clade; Eastern Sierra Nevada clade; and Rocky Mountain, Great Basin, and Mexico clade.
Interestingly, the Eastern and Pacific clades are more closely related to each other than to the two populations in between them geographically. Spellman and Klicka propose that as patches of pine and oak forest were isolated by changes in the North American climate and uplift of mountain ranges in the west, populations were isolated and diverged.
Then, late last year, a graduate student named Woody Walstrom published a new paper, with Spellman and Klicka, that studied 20 different sections of DNA (instead of just one) and found strong support for the same four populations identified in the earlier study.
Noting these results in combination with long-recognized (if subtle) morphological and vocal differences, the 2011 paper proposes that all four populations could be given full species status.
So far, only the IOC World Bird Names project has made any move to consider this proposal, noting “potential splits” of Pacific Nuthatch, Great Basin Nuthatch, and Mexican Nuthatch from White-breasted Nuthatch.
These names sparked a predictably snarky discussion in the BirdForum taxonomy forum, leading ornithologist Frank Gill (of the World Bird Names project) to comment: “These initial names are just placeholders. Recommended English names for these candidates await discussion and decisions on species taxonomy.”
It’s not clear when the AOU might take this up, but it’s certainly interesting to consider, and it fits with a general pattern observed in many North American species groups that have been split and lumped repeatedly over the years.
What do you think — are you ready for seven North American nuthatch species? What should we call them?
Personally, I remain very skeptical of many of these proposed splits. Most of these decisions are based solely on mtDNA, with limited follow-up studies on actual host species DNA, if any. While mtDNA can be a valuable tool, the possibility does exist for a greater variation in a population’s mtDNA than in their own DNA, and should not be the sole “evidence” for a split. Even mentioning morphological and behavioral differences do not cut it for me. All one ever has to do is look at dog DNA studies to quickly decide that morphology is also just not a good enough clue.
Hi, David. I was also hoping for some nuclear DNA work in this case, but apparently it hasn’t been done yet. You are right — it would help make a stronger case than mitochondrial DNA alone. But even if we get it some day (and assuming it were to show a similar result), it’s still largely a matter of style and preference as to whether largely allopatric populations with distinct histories and some genetic distance are split or lumped. Which should give us plenty to talk about for a long, long time.
So, is there any physical difference between the four? Are they going to split them and force us to collect DNA samples in order to figure out what we saw?
Brian, yes, there are some physical and vocal differences, as I mentioned in my post. Sibley’s field guide illustrates some of the plumages, and Wikipedia describes the differences here: http://en.wikipedia.org/wiki/White-breasted_Nuthatch#Geographical_variation. As for vocalizations, Nathan Pipelow has a good series here: http://earbirding.com/blog/archives/tag/white-breasted-nuthatch. Also, because the populations are largely isolated geographically, there are relatively few places where the identification should be challenging. One would not have to worry over every nuthatch in Ohio any more than one has to worry about identifying chickadees in Mississippi.
The great news is that I have seen all but the southeastern form. I love armchair ticks. I’ve always thought the birds east of the Sierra crest were much different than the birds in the Central Valley and Sierra foothills.
I find the idea frightening, intriguing, and pretty cool. But I think that the pacific form should be called Surfer Nuthatch just because the idea of a nuthatch surfing is amusing.
Great to see your always-interesting blogs at this site. I remember seeing a White-breasted Nuthatch at Boot Spring, Big Bend National Park, TX, with Colima Warblers. Which race or species would that be (interior west or eastern)?
Thanks, Jim. I have seen nuthatches in Boot Canyon too, and they sounded very different from the birds in the East. They are part of what the researchers call the “Rocky Mountain, Great Basin, and Mexico clade.” We can only hope for a less cumbersome English name if they are elevated to full species status!
“Species” is a term we use for our own convenience. Bird species can hardly be defined as non-breeding populations with all the crazy hybrids that turn up (the white throat X junco was neat). Because of the (apparent) uniformity, I’d say we have nothing to gain by separating them, and it certainly wouldn’t help beginning birders. I won’t say no to new checks either, so if we have to name them, we should call them (in whichever order) white breasted nuthatch, white faced nuthatch, white eyebrowed nuthatch and white submoustacial nuthatch.
Someone should create a new term to describe all these potential splits
(Crossbills, Fox Sparrows, Nuthatches, etc., ad infinitum). How about “orniflation”. One day the value of your life list will be close to zero, just like the dollar as the Fed keeps printing up more money.
This is where conversations such as these bother me. It seems that people are much more concerned about their life-lists (and the way this split would affect their life-list) than the correct scientific identification.