What is a species? (1 Viewer)

[Mysticete]

A hiccup with the WGAC process will be that in correspondence with BirdLife, I was informed that the participants are not putting a moratorium on new decisions. This means that quite a lot of the updates in each taxonomy are 'work as normal' assessments based on new evidence, rather than acts of unification. Each new decision is potentially a new area of disagreement to be resolved later. I thought it would have been wiser to have parked future decisions, until at least all the parties had agreed that they would be making the same change in future. Otherwise, it may be extremely difficult to finalize the project and sync all lists. The optimum time to try and do this would seem to be to target completion in early July, the end of the longest interval between the global taxonomy updates (IOC end of Jan and July, Clements Aug and BirdLife Dec).

I will not work through the update notices, but await the formal issue of IOC 13.2. It will however be interesting to see how IOC 13.2, Clements 23 and BirdLife 8 change the above calcs. How about a convergence clock with 1,000 differences representing one hour to midnight? (we would then currently be at 11:06 - 54 minutes to midnight!).

I recall one of IOC folks commenting here that IOC at least is putting a "hold" on new decisions relating to taxonomic change. The changes coming through here are either from the WGAC process or from decisions made by the North or South American checklist committees. Hence why we saw Northern Goshawk split, a NACC recent decision, and something I don't think any of the "Big 3" global checklists had followed through on. So at least one committee is sort of avoiding any new decisions.

Of course, I always got the sense that Birdlife International/HBW already didn't update to the extent the other global checklists did, at least in recent years.

 

[Mysticete]

I am guessing here, but I presume that we cannot determine whether species will have fertile young apart from through experimentation or 'mechanics' - i.e. I have read that falconers experimenting with birds have crossed Merlin and Peregrine, but only with male Merlins, as the eggs for a hybrid are two large for a female Merlin to carry and lay - again not sure if this is urban myth, but pretty sick if it is true. Through mechanics it is pretty obvious that some birds cannot hybridize successfully, but I think theses pairings are obviously different species in any case. I presume that we do not understand genetic information well enough to determine if a hybrid will be infertile in principle, through a mixing of genes (could we predict the gene mix for a start? I think that hybrid ducks quite often have types, so hybridization does not seem to produce infinite variation).

Assessing the possibility to hybridize and produce hybrid young, would be interesting for certain species which presumably have evolved from a common species and then become isolated and fragmented, perhaps through geological processes. As you say many Tapaculos very similar, and hybridisation cannot be assessed due to isolation - vocals here would seem to be the prime differentiator.

As a aide issue, it is interesting that I would expect certain species not to hybridize in the first place as the species are vocally distinct and therefore attraction should not occur in the first place. This does not seem to necessarily be true, with some interesting apparent hybrids recently found in Britain (Redstart x Winchat & assumed Whinchat x Stegner's Stonechat) - are these explained by forced opportunistic couplings with a properly paired female? In any case, a lack of vocal attraction, would seem to make assessment as to whether birds will hybridize and whether young will be fertile even harder to assess - just because species don't generally 'get it together in nature', may not mean they are not closely related or that they cannot produce fertile offspring.

For hybridization, it's not specifically if the hybrids are sterile or otherwise incapable of producing offspring, but rather if the hybrids have reduced fitness. Of course, being less fertile goes into that, but it also could mean a hybrid being less attractive to either species for mating, more prone to disease or injury, or some physiological adaptation or behavior that makes them less successful than pure birds of either species. A good example is Audubon's vs Myrtle Warblers. They will freely mate with one another, but despite this the hybrid zone has remained relatively stable and narrow, and the hybrids seem to be selected against.

 

[Jon.Bryant]

Hence why we saw Northern Goshawk split, a NACC recent decision

Thanks for the explanation. Of course this alignment with NACC recent decisions could still put IOC at odds with Birdlife - I presume that Clements are fairly well aligned with NACC in any case.

Of course, I always got the sense that Birdlife International/HBW already didn't update to the extent the other global checklists

My feeling is that they made a big step change some time ago, but have since slowed down. Perhaps becuase they feel they have got it pretty right already, and perhaps because changes are more difficult to implement.

I think that because they are tasked by IUCN with categorizing bird status as well as looking at taxonomy, the process for BirdLife to change is always going to be more laborious. Again don't take this the wrong away, but Cornell's Birds of the World includes quite a few articles where it states taxonomy to be updated. Conversely, the BirdLife data zone (which is hyperlinked to all their decisions) contains current information, including population sizes on all recognised species. In turn I believe that this information is fed through to the IUCN red book - presumably the IUCN also want a manageable process of change (and definitely not the Hudsonian Whimbrel, no Whimbrel, no wrong again, Hudsonian Whimbrel, type of rapid changes that have sometimes occurred with IOC).

I have always wondered why BirdLife made such a headache for themselves by developing their own global taxonomy, but perhaps controlling the change process and their downstream workflow is part of the reason, and perhaps why they are reluctant to commit to adopting the WGAC recommendations (and hence loosing control of the management of change).

 

[Jon.Bryant]

A good example is Audubon's vs Myrtle Warblers. They will freely mate with one another, but despite this the hybrid zone has remained relatively stable and narrow, and the hybrids seem to be selected against.

Very interesting, I am learning! I can imagine that this is even harder to try and determine, especially for birds that rarely hybridize (as they generally not attractive to each other, or are isolated). I can't imagine our knowledge of genes will every be able to answer will a hybrid be less fit or less appealing.

Interestingly hybrids appear not always to be weaker, as evidenced by the apparent success of Big Bird (Large Cactus Finch x Medium Ground Finch) reported on Galapagos - although I suppose it make take time to determine if there are more susceptible to some diseases that may not be widespread, or if in-breeding and lack of biodiversity finally weakens the hybrid population.

Again not trying to throw your argument, but don't NACC and Clements lump Yellow-rumped and Myrtle Warbler? If hybrids are indeed weaker, then why the lump? In 13.2 IOC split Audubon's, Goldman's and Myrtle, whereas Birdlife 7 splits Myrtle and Audubon's, but lumps Goldman's with the latter.

 

[Mike Earp]

... it seems like all of the world bird checklists are still onboard.

Apart from H&M and TIF, to name but two, which were never on board.

 

[Jon.Bryant]

How on earth did you crunch those stats so quickly!!!!

I have been trying to create a diary and listing programme for some time - I know there are tools out their, but I like BirdLife's taxonomy (missing from other packages, don't like Birdtrack's (IOC) non-existent filters for foreign birding, and rather like most UK birders, I like EBird's easy of use, but have hang-ups about using Clements - all those lovely albatross species lost for a start! Also, I would like to create a combined listing and diary system - I really don't want the faff of inputting all my dairies going back to 1983 into a system, just to have reliable lists, but I also get annoyed when EBird spits out stats based on only a few years or birding (and my incomplete submission of data for recent years in any case).

The reason I could crank the numbers easily, is because I have mapped all the differences and have a programme to check for changes in any in the three main taxonomies. I can therefore update the mapping fairly quickly - normally a few days after an issue of an update. I am currently working on making this a bit slicker. However, it has been a bit like painting the forth bridge, particularly in the early days and during the second half of the year, when more lists get updated. I have got to they stage where I can switch between global taxonomies and regenerate the three global taxonomies from my database. My recent challenge has been inducing 'necessary groups', i.e you don't need to record 'American' or 'Eurasian Goosander' (aka use all EBird groupings) to map between lists, but you do need some (say Goldman's, Yellow-rumped and Myrtle Warbler) to make it seamless. The ideal would be to have a system that allows Ebird groupings, but also has *groups 'required/mandated' for mapping purposes.

Finally, I will get all this done and the WGAC will make all the work redundant!

I first heard about the WGAC when I sent my mapping of differences to IOC, Clements and BirdLife with a plea to try and resolve the mess (if even to start with the low handing fruit of Latin nomenclature when taxonomy was unambiguous!) - this is still not complete! I even grouped my differences into subgroups, and advised on what I thought would be the most efficient changes to implement first - say the agreement on one genus name, can bring 50 alignments at species level and 200 at subspecies level!

Anyway, I was pointed to the WGAC, so now am a little in limbo - continue to map and plan (as I am doing) or wait for unification (which I am not entirely confident will ever happen [BirdLife have not currently fully committed] and may be transitory, particularly if global taxonomies are not abandoned in light of the WGAC list, but continue to be updated. Whose to say, even a new list may materialize and challenge for supremacy (another Sibley & Munroe, Peters, H&M etc, with their moment in the sun).

I suppose ditching the mapping, selecting a taxonomy, and basing a system on that would be the smart thing to do!

 

[Jon.Bryant]

Apart from H&M and TIF

H&M were apparently invited, but didn't participate as they wanted to protect their intellectual property. A bit odd, as (perhaps a bit rudely) I suggest that the their intellectual property is not maintaining its value and is probably falling sharply! - No updates since version 4 in 2016, and one of the adjudicators I know said 'never again' after that last release.

I can't see many ornithologists opting for H&M, particularly when other lists are free to download and up to date - the model or paying for a taxonomy, in the present day seems flawed. I suspect that many people who bought the hardback version 2, have now moved on to a free alternative, and that H&M is in terminal decline. The Howard & Moore Website has not been updated since May 2020, and I cannot even open www.howardandmoore.org, as I get a security alert that the security certificate is invalid and the page unsafe. NHBS list the hardback as 'out of print', so unless you want to go to the second hand market, it is difficult to even get your hands on.

That said the WGAC website says, 'Heading the project are Les Christidis, WGAC Chair and former co-editor of the passerine volume of the Howard & Moore Complete Checklist of the Birds of the World edition 4...' I think the important word here is former.

I hadn't looked at the TIF, but it doesn't seem to have been updated for 4 years, although a very impressive endeavor, as it seems to been the genius of one man. Notes suggest that it is H&M, argmented with a with a large dash of IOC, and a touch of BirdLife and Clements. Not sure if the list is therefore based on first hand review of the scientific information, or if more of an amalgamation of the work or others. If the latter, it would be reasonable to not include the author in the WGAC.

 

[cajanuma]

Again not trying to throw your argument, but don't NACC and Clements lump Yellow-rumped and Myrtle Warbler? If hybrids are indeed weaker, then why the lump? In 13.2 IOC split Audubon's, Goldman's and Myrtle, whereas Birdlife 7 splits Myrtle and Audubon's, but lumps Goldman's with the latter.

Here is the proposal to split Yellow-rumped Warbler: https://americanornithology.org/wp-content/uploads/2020/02/2017-A.pdf (page 46)

And here are the comments on that proposal: Comments 2017-A - American Ornithological Society

As you can see, it was an even split. I find I always learn a lot from reading these proposals and the associated comments, and I think the Yellow-rumped Warbler case is a perfect example of just how arbitrary some of these decisions have to be. I really think both positions (split vs lump) are equally valid, and there's no right or wrong answer.

 

[Mike Earp]

I hadn't looked at the TIF, but it doesn't seem to have been updated for 4 years, although a very impressive endeavor, as it seems to been the genius of one man. Notes suggest that it is H&M, argmented with a with a large dash of IOC, and a touch of BirdLife and Clements. Not sure if the list is therefore based on first hand review of the scientific information, or if more of an amalgamation of the work or others. If the latter, it would be reasonable to not include the author in the WGAC.

The latest TIF update seems to have been on 25 October 2021, so less than 2 years ago. I think John H Boyd III based TIF on first hand rteview of the literature. It is a great shame TIF is not being maintained.

 

[jurek]

Just few points.

My understanding is that they have a proposal system, that requires each taxonomic discrepancy to be explained with arguments made for and against a split

Collecting similarities and differences in a worthwhile task. But the other half of the system does not exist. As you don't work with bird taxonomy, you may be unaware of it. There is no set which species and which differences are sufficient for a species level. The similarities and differences are rarely challenged, it is that opinion whether they are sufficient for a species changes.

it assumes that the threshold value will represent the same point in all species within the speciation process. We know however that there are birds with fairly low genetic divergences that behave as good species.

For allopatrics, it is possible to come up with objective measures by comparing differences between allopatrics versus those between sympatrics.

Current knowledge of genetics and ecology basically say that there is no such fixed point. Because genes and traits evolve mostly independently, and selection acts with different strength at different populations.

Therefore genes responsible for species compatibility will not follow others, and that one population is a species do not mean that others, even closely related, evolved into species, or are reproductively incompatible etc. As already correctly explained with examples such as large white-headed gulls.

In fact, scenario where a sub-population of birds evolves into a different species but the more diverse parent populations don't should be very common in e.g. birds colonizing small islands from the mainland, or any isolated mountain chain, region etc.

For hybridization, it's not specifically if the hybrids are sterile or otherwise incapable of producing offspring, but rather if the hybrids have reduced fitness.

Note that hybrids issue is often more complicated - European Pied and Collared Flycatchers hybridize despite hybrids being partially infertile, because fertile hybrids have apparently higher fitness.

However, in my experience, most problematic examples in bird taxonomy are not complex hybrid situations. It is mostly splitting parapatric populations which cannot hybridize. or populations where hybrid zone is unstudied - because it looks good on paper. Our outright ignoring evidence for hybridization.

An example is the below paper from 2007 showing low difference and gene flow between Eastern and Spanish Imperial Eagles. 16 years later, to my knowledge, the paper was not challenged, but no move to lump the species was made.
Genetic evidence for a recent divergence and subsequent gene flow between Spanish and Eastern imperial eagles - BMC Ecology and Evolution

 

[Mysticete]

Apart from H&M and TIF, to name but two, which were never on board.

H&M has legal barriers tied to the endowment that funds the checklist that prevents them from directly participating in the WGAC, IIRC. However some of the people behind that checklist are on the WGAC committee. So in some informal sense H&M is involved

TIF is a great resource and I respect John Boyd and his work on it. I refer to it all the time. But lets keep things in perspective. John Boyd is an economist by trade effectively an amateur taxonomist. TIF is his personal website and hobby. I see no reason why TiF would be brought on board, nor do I think the would be especially interested.

 

[Mysticete]

Here is the proposal to split Yellow-rumped Warbler: https://americanornithology.org/wp-content/uploads/2020/02/2017-A.pdf (page 46)

And here are the comments on that proposal: Comments 2017-A - American Ornithological Society

As you can see, it was an even split. I find I always learn a lot from reading these proposals and the associated comments, and I think the Yellow-rumped Warbler case is a perfect example of just how arbitrary some of these decisions have to be. I really think both positions (split vs lump) are equally valid, and there's no right or wrong answer.

Indeed the Yellow-rumped Warbler case is a perfect example of how people who claim to use the same species concept can still argue over its interpretation. Some of the people voting no were using a far more strict version of BSC than the people who voted yes, specifically discounting postzygotic barriers.

 

[Mysticete]

An example is the below paper from 2007 showing low difference and gene flow between Eastern and Spanish Imperial Eagles. 16 years later, to my knowledge, the paper was not challenged, but no move to lump the species was made.
Genetic evidence for a recent divergence and subsequent gene flow between Spanish and Eastern imperial eagles - BMC Ecology and Evolution

Mitochondrial Control region DNA is considered to no longer be sufficient for the purpose of taxonomic change. It doesn't surprise me that it hasn't been acted upon.

 

[Jon.Bryant]

is unstudied

A suggestion I made to Cornell, was whether through a University website, the University could engage citizen science to collate missing information for species assessments. Many of us travel a lot more and have appropriate equipment (high res cameras, sound recording equipment etc.), so could potentially fill in some of the gaps in knowledge. This would be a bit different to their excellent resources on EBird and the Macaulay library, as it would be to document specific data (e.g. abundance and characteristics of hybrid populations, consistency of morphological or acoustic differences etc.). I suppose that as citizen scientists have collected DNA for vagrants, we could even be instructed on how to do this for target areas of interest, although the issue of how tests would be funded would be difficult to resolve.

Unfortunately I have had no response - not sure if this was because taxonomy is seen as the pursuit of 'proper scientists' that cannot be trusted to 'citizen scientists', or they have no interest, time or resource for implementation.

I think is a shame as

1. I think it would provide some accountability if taxonomic committees clearly explained information the deemed insufficient and lacking for proper assessment.
2. Citizen science has been used relatively effectively to determine distribution, and has been used well to share photographic and sound information for study and identification purposes, so why not mobilize that 'workforce' with specific tasks related to try and resolving taxonomic issues.

I am sure there must be plenty of Spaniards with huge experience of Spanish Imperial Eagle, and either already know hybrid criteria or could assess birds observed, if they were advised what to look for. I suspect however, that from a distribution perspective, hybridization is likely a very rare event.

As a side issue (and at risk of inflaming an old argument), I contacted the person who wrote the paper on why Thayer's Gull is a valid species, which appeared in Dutch Birding (I am aware that the Dutch taxonomy is based in PSC, not BSC). I asked if he was going to submit his paper to NACC, to which he replied that he had previously submitted several papers, some of which had been accepted and other rejected, but he would not be submitting a paper on this occasion - I got the distinct opinion that he considered that NACC do not want to open a fresh wound, and that the outcome may therefore be prejudiced. However, his paper raised some interesting points regarding Thayer's Gull, which suggest that hydridisation may be rarer that we think (and this conclusion was stated to be substantiated by personal observations of some eminent gull experts). Many of these points, such as differences in vocalisation, could be readily proven of disproved by mobilizing citizen scientists. I personally think it is a great shame that there is clearly a substantial lack of knowledge about this gull - as stated by some of the members of the NACC committee during the assessment - but there seems to be a lack of appetite to try work to fill the knowledge gap. If we are to rely on someone visiting the high arctic to study this gull, I suspect we will wait for ever - proving or disproving a taxa which may well be a hybrid swarm, hardly sound like a glamorous of attractive endeavor, and hardly likely to attract research funding.

 

[Mysticete]

I am skeptical that "citizen science" can help with the Thayer's Gull situation, given that the hybridization that is occurring would be in the high arctic. Not exactly an easy area for the average birder to assess!

 

[cajanuma]

As a side issue (and at risk of inflaming an old argument), I contacted the person who wrote the paper on why Thayer's Gull is a valid species, which appeared in Dutch Birding (I am aware that the Dutch taxonomy is based in PSC, not BSC).

I am not sure what species concept Dutch taxonomy is based on, but it cannot be the PSC as the Dutch Birding list of Western Palearctic birds includes subspecies, and the PSC, by definition, does not recognize subspecies. Under the PSC, the species is the smallest taxonomic unit, so any taxonomy that includes subspecies cannot be PSC.

 

[Kirk Roth]

I am skeptical that "citizen science" can help with the Thayer's Gull situation, given that the hybridization that is occurring would be in the high arctic. Not exactly an easy area for the average birder to assess!

Beyond that, taxonomy is an example of a discipline that has moved beyond where citizen science can help. Unless genetic categorization becomes accessible and popular to the "citizens," even the best of photographic catalogues will be of limited use, given where the bar is currently set for real decision making.

That said, I've seen citizen recordings used to inform taxonomic decisions - I occasionally bump into references to Xeno-Canto in the discussions on both AOS committees' comments.

 

[Kirk Roth]

I am not sure what species concept Dutch taxonomy is based on, but it cannot be the PSC as the Dutch Birding list of Western Palearctic birds includes subspecies, and the PSC, by definition, does not recognize subspecies. Under the PSC, the species is the smallest taxonomic unit, so any taxonomy that includes subspecies cannot be PSC.

"What is a subspecies?"

Under Ernst Mayr, and especially under a lot of writings in the 19th and 20th centuries, subspecies were those populations which exhibited phenotypic differences, yet integrated. Though the definition of "subspecies" has been debated for all that time too.

For a PSC species, the taxon must be both diagnosable and discreet. The logical following would be that if a taxon were discreet it is a species and if not discreet it is a subspecies. If that is not PSC, then what is the name of such a system? And if it exclusive of PSC, then how does PSC handle intra-specific variation?

 

[Mike Earp]

You could try reading Jerry Coyne and Allen Orr's book "Speciation". Executive summary: there's about 20 different ways that scientists classify species. Fortunately (for us here) there's only 2 or 3 which are used by ornithologists, and BSC is leading the pack.

Unless I missed it, I don't think anyone has suggested referring to An overview of speciation and species limits in birds by Kevin Winker (2021, Ornithology 138: 1–27). It's much more recent and is freely available. Speciation in Birds (Price 2007) is older but also looks potentially useful judging by this review.

 

[Jon.Bryant]

Beyond that, taxonomy is an example of a discipline that has moved beyond where citizen science can help.

Really? I am only thinking of supporting information, but if we look at Thayer’s Gull as an example

• Do we witness pair bonds being formed on the wintering grounds, as has been suggested?
• If so, what percentage of pair bonds observed during late winter/spring involve birds of mixed characters?
• What percentage of typical Thayer’s type birds do we encounter on the east coast, or of Kumlien’s types on the west coast during winter months?
• Are vocalisations of Thayer’s and Kumlien’s distinct as suggested?
• If long calls are distinct do playback experiments to the other form, illicit any form of response?
• Are there any behavioural differences, or when seen together, does one form dominate the other - say during aggressive displays over food resource?
• Does the age mix of migratory flocks, indicate migration routes are learnt or inherited? In particular do ‘fresh’ mixed character first-winter birds typically associate on migration with mixed character adults, or also with ‘pure’ adult types?
• What is the true variation in plumage pattern where one type or the other is the norm?
• What is the winter distribution and population estimates for mixed character birds - I think in a previous thread someone said mixed character birds are the norm in the Great Lakes area, whereas it seems from literature that mixed character birds are rare at least on the west coast.

More straightforward I have seen ‘decisions’ for other ‘failed’ species that say, lack of complete study of vocalisations, lack of knowledge of field characteristics in potential area of overlap, not demonstrated that morphological differences are consistent etc. Similarly, some reports on ‘passed’ species have stated that subtle morphological differences exist (which I then can’t find referenced to in any ID guides, presumably indicating these differences were previously undocumented/unknown). Surely these types of issues are all things we could help to answer, when we are in the right place and have been told what is wanted?

If Killian Millarny can solve the ID of Saunder’s Tern, starting from an online image search, then I am sure a good collation of relevant photos and sound recordings should be of value to researchers working on specific taxonomic issues.

I remember a long time ago corresponding with Xeno Canto about ‘projects’ to target and collate bird vocalisation info - I wasn’t very articulate with my idea, and they got a bit excited about something rather different instead. I wanted a system to mobilise amateur recordists to undertake specific recordings - my interest was particularly in the ‘rumour’ that Pale-legged and Sakhalin Leaf Warbler contact calls were at different frequencies. I really think that if they had set up a system where researcher could ask birdwatchers to target certain species in certain areas, issues like those two leaf warbler vocals would have been proven much earlier and much more easily.

Surely a system that could mobilise birdwatchers to try to seek answers to specific questions could only aid both taxonomy and identification research.

To suggest that taxonomy is so elevated, that ordinary birdwatchers cannot even assist seems perhaps a little pompous and narrow minded - I am only suggesting we could act as extra eyes are ears to undertake field observations after all.

I suspect that it would only work for papers that had failed due to lack of sufficient evidence, as I doubt researchers would initially want to divulge their research direction to others, and before they had submitted a paper.