AOU Checklist News!

The North American Checklist Committee of the American Ornithologists’ Union has published the results of its deliberations on the first round of proposed changes from 2009, and it has updated the slate of proposals currently under consideration.  Here’s a quick summary of the changes that affect species splits north of Mexico.  (I won’t get into all the changes to scientific names, even though those topics are just as interesting in my opinion — you can click through to read about those yourself.)

Proposal accepted

This split will become official once the next checklist supplement is published in the July 2010 issue of the Auk.

  • Split Pacific Wren from Winter Wren. As I reported earlier, this split did indeed pass, and unanimously at that.  However, note that the names “Pacific Wren” and “Winter Wren” are not final.  The committee is considering an addendum to the proposal that would split eastern North American birds from Eurasian birds and change the names of the American species to “Western Winter-Wren” and “Eastern Winter-Wren.”  Stay tuned.

Proposals rejected

In most cases, a 2/3 vote of the committee is required for a proposal to pass.  These proposals failed to muster that level of support:

  • South Hills Crossbill. The proposal to split South Hills Crossbill (Type 9) from Red Crossbill failed on a vote of 6 “yes” votes to 5 “no” votes, with three of the “no” voters indicating that they would be open to changing their minds if presented with more data.  Two of those voters preferred to deal with the North American Red Crossbill complex as a whole, rather than splitting one type at a time, piecemeal.  Thus, most of the committee appears to accept that the different call types of Red Crossbill are likely good species, but I think it may be a while before those species appear in your field guide.
  • The split of Western Scrub-Jay. The proposal to split the interior “Woodhouse’s” Scrub-Jay (woodhousei) from “California” Scrub-Jay (nominate californica) failed on a vote of 7 “yes” votes to 5 “no” votes.  Many members of the committee felt that more data were needed from contact zones.  The tagalong proposal to split the southern Mexican subspecies sumichrasti into yet a third species gained even less committee support.  Vocal differences between woodhousei and californica have been reported, and you can expect those differences to be discussed in a future post on this blog.

New proposals

The checklist committee never sleeps.  The following splits of North American species are now under consideration:

  • Split Black Scoter (Melanitta americana) from Common Scoter (Melanitta nigra).  I wrote about this split recently.  This proposal was originally submitted in 2006 and failed to pass at that time, but the recent publication of Sangster (2009) has revived it.  Personally, I think it’s a clear-cut split, but we’ll see if the committee agrees.
  • Split Curve-billed Thrasher (Toxostoma curvirostre) into two species: the western palmeri group and eastern curvirostre group.  The proposal makes no recommendation regarding the resulting English names.  The proposal cites various genetic data, which I won’t comment on, but it also cites vocal differences, including differences in calls.  I’m a little skeptical of these differences, but I’ll investigate them in the future and report back on what I find.
  • Split Whip-poor-will (Caprimulgus vociferus) into a nominate eastern species and the southwestern arizonae species, on the basis of subtle but easily diagnosable differences in song, differences in egg coloration, and (most importantly) a hot-off-the-presses study demonstrating that the vociferus and arizonae groups may be as genetically distinct from one another as either is from the Dusky Nightjar (C. saturatus) of Costa Rica and Panama.  I haven’t been able to track down the article text yet, so I can’t say what I think of it.

As you can see, vocal differences are playing an ever-more-prominent role in taxonomic decisions.  Look for more on this topic from me in the future.

21 comments to AOU Checklist News!

  • The failed South Hills Crossbill split is disappointing, but good for the Winter Wren. Though the proposed names Eastern and Western Winter-Wren are absolutely brutal. Come on, AOU! Let’s have a little creativity!

  • I agree with Nate on the proposed names for the Winter Wren split. The “Winter-Wren” formulation is particularly clumsy. Why not just use English equivalents of the existing subspecies names, pacificus and hiemalis?

  • Nathan Pieplow

    I’m with you guys. I don’t see a problem with “Pacific” and “Winter,” especially since neither of those names is in common usage for the Old World species. The only potential pitfall would be in confusing “Winter Wren” (sensu lato) with “Winter Wren” (sensu stricto).

  • Great news for the wrens, although I’ll echo comments on the awfulness of Eastern and Western Winter-Wren. There is nothing wrong with Pacific Wren.

    Disappointing about the scrub-jays, although it is also disappointing that no one has yet studied the contact zone rigorously. Hopefully soon.

    On crossbills – I’m not disappointed. I’m still trying to wrap my head around the notion of defining a species whose only diagnosis is call type, a learned trait that can be changing by individuals. If an individual can just change its call type and thus jump from one putative species to another, I just don’t see labeling them all as species.

    On Whips – I have the paper if you want it, just email me. It doesn’t devote much more than a sentence or two to the vociferus split, but I think it is valid.

  • Dan Lane

    Regarding the crossbill biz, I’ve been less inclined to see the different voice-types as “species” ever since I learned that individuals have been documented to change their calls as adults. If the calls are not innate (eg, genetically programmed… as calls usually are for most birds, or at least so we think), then they are not likely to be effective isolating mechanisms preventing interbreeding of different populations. Bill sizes are important for being able to eat the locally important seeding conifer, but bill sizes are also not isolating mechanisms since there are frequent-enough irruption events that force crossbills of a given bill-type to forage on a seed type for which their bills are not evolved to eat… and during these irruptions, types with different bills and calls are often found together, increasing the chances that they might interact and interbreed. Such irruption events are probably the important ones to maintain isolation or permit interbreeding of different voice and bill-types of crossbill. Thus, genetic markers would be one of the most important means by which to understand if these forms of crossbill are truly on their own evolutionary trajectories or not. Also important would be continued marking studies to see if individuals form mixed pairs, etc (although this would require a huge amount of work in capturing thousands of individuals to find only a few cases of confirmed mixed-pairs). Finally, if the call notes cannot be used as definitive characters to identify crossbills (due to the afore-mentioned fact that individuals can copy and/or change the call type they learned), then how are we identifying crossbill types without a lot of error? This quandary is as relevant to South Hills crossbills as to all other North American (and, presumably, Eurasian) types.

    Of course, apart from the South Hills form (for which a new holotype specimen was designated) the added problem with other crossbills is that it is not clear which names (already created and, by the International Code of Nomenclature cannot be dismissed without failing every effort to retain them) belong to which call/bill types. This will slow down that process considerably… again, genetic markers will be important (assuming that ancient DNA techniques can be used to recover useful sequences from the type specimens) and that these markers will have meaning with relation to bill and voice types now known to exist.

  • Charles Swift

    I guess Pacific Wren is ok but I’m pretty sure there are not other birds with Pacific in their common names that nest in Idaho! Except for perhaps Pacific-slope Flycatcher which may breed in northern Idaho and probably does in eastern B.C. (see the recent Rush et. al paper on this –

  • Carson

    @Charles, not to worry; in a few more years there will be an Idaho Wren, which will eventually be split into a Western Idaho Wren and an Eastern Idaho Wren; the Eastern Idaho Wren being eventually changed to Summer Wren.

  • Nathan Pieplow

    The fact that crossbills can change call type as adults freaks a lot of people out. But the underlying genetics of those individuals, and their bill morphologies, don’t change. They are very rare (at least in the Idaho study — there was only one documented), partly because (in theory) their hybrid offspring will be selected against. Evolutionarily speaking, these birds that have paired with the wrong type have made a poor choice. In my view, it’s basically the same situation as with any hybrids (Indigo x Lazuli Bunting, for instance) — it’s just that birders react differently on a psychological level.

  • But recognizing the differing underlying genetics and bill morphologies are dependent upon classification based on call type! With the bill morphologies, the groups differ on average but with huge overlap in range – check out Table 1 in the paper describing L. sinesciuris. Similarly, for the genetic data in the form of AFLP markers in Parchmen et al 2006 and in the L. sinesciuris paper, the groups differ on average in allele frequencies but there are no fixed differences. There are not obvious segregating groups defined by the genetic or morphology data independent of the information provided by call type. I am not implying that there are not distinct groups corresponding to call type, but that the boundaries between these are defined by something that is not innate or fixed. It is then almost impossible to actually measure gene flow between these groups, because you can never really tell to what group an individual belongs. In my mind, the only sure way of doing this is to do the direct studies of marked individuals, but including individuals known since birth so any change in call type can be documented concretely. That is a tall order!

  • Nathan Pieplow

    It’s true that proving the isolating mechanisms to that higher standard is going to be a tall order. Crossbills are messy, messy, messy. But that’s why they’re rewarding to study, too.

  • K. Cowcill

    My first thought on the Whips was to split them–I’ve seen both so I’d get another bird for my list. I know, not very scientific, but I’m taking a day off. :)

  • Matt Young

    While I certainly will not claim what call types might and what call types might not be full species (at least not at this point), the South Hills Crossbill study certainly seems to fit the bill as a species. I find it incredibly unfortunate that many want to continue to point to a single bird changing it’s call out of dataset of 3400 individuals over 10 years. Clearly we all know that mis-imprinting takes place and we’ve all surely heard birds singing funky songs. Personally I’ve heard a Yellow-rumped singing a Black-throated Blue song and a Cerulean Warbler singing a Northern Parula song. We should all take a serious look at the complex regardless of our birder bias. If types pair with their own type like they did >99% in Benkman’s study of types 2,5, and 9 or Groth’s (1993) study of 100% between types 1 and 2 but sample size of only 30 and Summers et al. (2007) ~95% between Common, Scottish and Parrot Crossbills, then we should give the complex the closer look it deserves. The amount of hybridization found so far in these studies is much less than many already easily accepted and recognized species. If they can recognize each other than it shouldn’t matter what we think. Surely more exhaustive studies are needed, but it seems Benkman’s study was more than exhaustive.

  • Matt Young

    Also, Benkman’s study included 3400 “marked” individuals. The fact there’s little fixed genetic differences is not surprising given we’re talking about a group of cryptic or incipient species that have only started to diverge anywhere from ~5-10,000 years ago. There are other recognized species that also show no fixed genetic differences– Redpolls come to mind (Suetin et al. 1995) and there are others as well.

  • Dan Lane

    To Matt,

    The issue here has nothing to do with *song* copying or learning. It’s the *calls*! If only one bird out of 3400 (which is a pretty high percentage, by the way, particularly given the relatively short time span of the study) is *documented* to have changed its call type in its adult life, how can we be sure that others did so but before they were captured and marked the first time? Or that the same individual may give more than one call type regularly? The real problem is circular reasoning: if we are identifying Red Crossbills to “types” based on call notes, but those call notes can be learned and one individual can give more than one call note type… well, how useful are these call notes to identify real, definable populations? How do you know that all individuals that are giving the same call note in a flock are not of different origins, and simply are copying one another to maintain flock cohesion? The researcher would have to tape each individual for an extended period of time, capture it, mark it, take a blood sample (and here we get into the murky territory of unvouchered tissue samples, which is a whole ‘nother can o’ worms), and then record it with another flock (not all necessarily in that order) to see what kind of bill type, genotype, and call types it expresses. Benkman did not do this, nor could it be done in a feasible way for 3400 individuals. Probably, this could only be done reasonably in captivity, but then the system and conditions would not be “natural”.

    The fact that call types can change weakens their usefulness as a solid character for identification to population, and that in and of itself, causes the foundation of the “several incipient species” idea to crumble. I’m not saying that Red Crossbills are not fascinating to study, they certainly are, and clearly they provide a unique system in Holarctic (and perhaps worldwide) bird population dynamics. But whether any North American populations will be found to be good Biological or even Phylogenetic species?… well, I have growing doubt. There are too many confounding factors to our ability to detect and distinguish types, there too few apparent isolation mechanisms, and there are still issues with the standing nomenclature (granted, that has nothing to do with the true relations between populations, just with our ability to place names on them). Still, it’s a subject worth continuing study… who knows? Perhaps all these fears may yet be put to rest!

  • Matt Young

    I understand it’s a murky complex in need of more study, but 1 individual of 3400 marked individuals over 10 years is not a high percentage. As for call switching, read — Limited adult vocal learning maintains call dialects but permits pair-distinctive calls in red crossbills Kendra Sewall 2009 and
    Social experience modifies behavioural responsiveness to a preferred vocal signal in red crossbills, Loxia curvirostra
    Kendra B. Sewall, a, and Thomas P. Hahn1, a– these studies were of captive individuals. Calls are also copied in crossbills and calls appear to be universally accepted as indicative of genetics more than song.

  • Dan Lane

    Matt said: >Calls are also copied in crossbills and calls appear to be universally accepted as indicative of genetics more than song.<

    That's my point Matt. Usually this is the case… Because calls are usually thought to be *inherent* (=genetically programmed) not *learned*. However, as your citations (which I can't access for the time being since I am out of the country) point out, these calls are *learned*, therefore their usefulness to assess genetic relations is moot. Thus, using calls, which are learned, to define groups leads to circular reasoning when trying to define said groups as taxonomic units. I will add that 1 individual from 3400 in 10 years is only the number of *detected*, not actual occurrences of call switching among the crossbills sampled. There may have been no others that did so, or there may have been many others that switched calls but were not *detected* among this sample of 3400… and even if not, in a genetic sense (assuming this call-switcher also interbred with the larger population), even such a low number of "assimilations" of members of one population into another would be enough, over evolutionary time, to maintain a relatively undifferentiated gene pool (read: keep these populations as one Biological Species). It takes a remarkably low number of such assimilations to keep gene pools relatively homogenious (this is basic population genetics).

  • Dan Lane

    Second part:

    Nathan said: >But the underlying genetics of those individuals, and their bill morphologies, don’t change. They are very rare (at least in the Idaho study — there was only one documented), partly because (in theory) their hybrid offspring will be selected against.<

    I think this is a bit of a fallacy, Nathan. The bill morphologies are likely to change within populations over time, and probably rather quickly (something rivaling what has been documented within Galapagos finches, I bet). I'm saying this without any data before me, mind you… but given how often crossbills are forced out of the conifers for which their bills are evolved (as we all know, this happens perhaps once a decade, if not more frequently), and into conifers of other-sized cones, hybrids and birds with non-typical bill morphologies would be selected for. Thus, I suspect that hybrids among crossbill populations may actually be very important members of flocks… and my suspicion is that a given population probably goes through waves of bill sizes over the centuries. This absorption of odd birds and hybrids into flocks would explain the low genetic variability that has been observed within crossbills… The maintainence of call types among members of a flock probably helps to maintain the cohesion of said flock… but it may be nothing more useful than that (think of humans and our languages… these languages, though useful to maintain political and cultural units, do not necessarily reflect genetic pools–in fact they nearly never do!). This is my argument, anyway… and I suspect it is the "null hypothesis" that would need to be debunked to show that each call type of crossbill is actually a genetic population on its own evolutionary trajectory and therefore a Biological (or for that matter, a Phylogenetic) Species.

  • Nathan Pieplow


    I basically agree with everything you’ve just said. The spirit of my comment was this: if differences in calls are almost always indicative of a bird’s morphological and genetic group, then I have no trouble using those calls to identify birds as a member of that group, even if the calls are learned and can be mis-learned or changed in a small percentage of individuals. How deep and abiding are the separations between the morphological and genetic groups? I leave it to the ornithologists studying these things to gather the data and convince people.

  • Matt Young

    Dan et al.,

    Even for species that learn their calls, it’s still thought that calls depict genetics to some degree. Yes, it would be less for a crossbill than for some flycatchers. Learning of calls takes place within the first days of life, whereas learning of song wouldn’t take place for most species until many months later.

    Benkman did measure each bird as well, but of course there’s morphological overlap between types 2, 5, and 9. There will always be holes to poke in this debate. I guess it all comes down to whether one wants to be believe or not believe crossbill flight calls are stable over time….and/or that they can be used as something to perhaps determine a scientific unit/species. Sewall’s paper is a good read. She basically housed types 3 and 4 together and in all cases birds did not change their call to match another call type. In fact, in one instance, a type 4 housed in the same chamber with a type 3 actually call matched a type 4 in a different chamber –the two type 4′s had no prior physical interaction. Her study spanned 2 years.

    Here’s Sewall’s abstract — Limited adult vocal learning maintains call dialects but permits pair-distinctive calls in red crossbills:

    Vocal imitation can inform receivers about the social background of signallers because shared signals reflect learning experiences. Open-ended imitation can generate shared signals that indicate current social affiliation, whereas limited vocal plasticity in adulthood can permit signals to reflect an individual’s origin. I examined the relations between vocal learning, signal sharing and social dynamics in red crossbills, Loxia curvirostra. Two levels of shared variation exist within crossbills’ contact calls: discrete call variants distinguish ecologically diverged crossbill forms, and within these variants, some bonded pairs produce calls with nearly identical structures. Assessment of vocal and social behaviour of experimentally housed birds revealed that some adult crossbills converged on calls shared with companions of their own form, but no birds learned new, categorically distinct call variants. Also, while the process of call convergence within the bounds of discrete variants was associated with affiliation, birds that produced different contact call variants interacted less frequently and less amicably. These results suggest that call learning is limited in adult crossbills, generating calls with two levels of shared variation and multiple social functions: discrete contact call variants reflect birds’ ecological forms, while pair-distinctive calls within those discrete variants reflect current social affiliation. Thus, a single social call concurrently reflects bonding among conspecifics of common origin and promotes the social isolation of ecologically diverged forms of red crossbills.

  • Matt Young

    I’d like to clarify this one comment from above: In fact, in one instance, a type 4 housed in the same chamber with a type 3 actually call matched a type 4 in a different *part of the same chamber* –the two type 4’s had no physical interaction, but did have audio contact during the study. Her study spanned 2 years.

  • [...] the annual update to the American Ornithologists’ Union Checklist.  That means the splits I blogged about recently are now [...]