New unified list of birds - Avilist (4 Viewers)

[Andy Adcock]

I do not think that genetic difference precludes interbreeding, so genetic difference does not make taxa behave as single species - it takes quite a long evolutionary process to stop 'that fitting in there' and 'this working with that'. So it is really just an indication that they have diverged a long period of time ago, and since mainly kept separate (dependent on gene flow). And of course if the populations have become isolated because of geological processes, even the lack of gene flow is open to interpretation - they act as two separate species because of their genes or because of a physical divide?

If we adopted rigorous DNA results, we would probably be rather upset . A fairly recent paper in Dutch Birding showed that up to 9% of Pallid Swifts in some colonies show gene flow with Common Swift!

Historically, the classic interpretation of a species would preclude any resultant offspring from being viable?

 

[Thijsdekruif]

We may have grown to rely on genetic difference, but is it the answer. As I say above I think most taxonomies now use the Tobias system, so DNA is only one criteria considered.

The problem with many of the morphologic differentiation is that is focuses on differences that humans can observe. And quite often this is not how nature works. Where is smell, infrared colouration and much more? Taxonomy has taken some steps, but still is quite close to how it worked in the 19th century.

 

[Jon.Bryant]

Historically, the classic interpretation of a species would preclude any resultant offspring from being viable?

As per a previous thread, I think this comes from our experimentation with domestic animals - the story that mules (horse x donkey) are always infertile etc.

It would be a hell of a job to prove hybrid infertility in the field - Are Pallid x Common Swift and Blyth's Reed x Reed Warbler offspring infertile, or even the more weird Redstart x Whinchat? I am pretty sure that second generation Pied Flycatchers x Collared Flycatchers have been proven to be fertile and even more sure about duck and gull hybrids.

It is also a difficult criteria to apply to species that do not come into contact. I think, there are no genetic rules that we can apply to say 'if that crosses with that, it will be infertile'. We would then have to do physical experiments by bringing separate species artificially together - a lot of work, and probably a touch unsavory/unethical to try and force cross breeding.

 

[Thijsdekruif]

Historically, the classic interpretation of a species would preclude any resultant offspring from being viable?

This is a bad thing. Most duck species can interbreed and produce fertile offspring (I remember some research that Stellers Eider is probably a result of interbreeding between long-tailed ducks and an ancestor of the Eiders). We would probably end up with only one Aythia species.

 

[Andy Adcock]

As per a previous thread, I think this comes from our experimentation with domestic animals - the story that mules (horse x donkey) are always infertile etc.

It would be a hell of a job to prove hybrid infertility in the field - Are Pallid x Common Swift and Blyth's Reed x Reed Warbler offspring infertile, or even the more weird Redstart x Whinchat? I am pretty sure that second generation Pied Flycatchers x Collared Flycatchers have been proven to be fertile and even more sure about duck and gull hybrids.

It is also a difficult criteria to apply to species that do not come into contact. I think, there are no genetic rules that we can apply to say 'if that crosses with that, it will be infertile'. We would then have to do physical experiments by bringing separate species artificially together - a lot of work, and probably a touch unsavory/unethical to try and force cross breeding.

Many species which have been split e.g Cutia, do not respond to each other vocally, outside of their natural range and vocalisations do play a fairly large part these days in touted splits afaik.

 

[Jon.Bryant]

The problem with many of the morphologic differentiation is that is focuses on differences that humans can observe.

Wondering considerably... but yes our perception of difference is different to the animal kingdom. I think most birds have a relatively poor sense of smell, and I am not sure any have infrared vision, but they can detect polarised light differently to us. But I do think that the main difference is that their cognitive abilities are on a different timescale to ours. We build a complex model of the world around us, but rather slowly - when I just heard a Wren outside, I recognize it as a Eurasian Wren, but no more. I suspect that another Eurasian Wren would know whether the sound was from a known neighbor or a new rival, it has the ability to hear detail that is lost in my slow thinking brain. How else can Sandwich Tern chicks recognize the calls of their parents, which even when I look at a sonogram all calls appear remarkably alike?

So yes, what appears the same to our cognitive abilities may be more distinct to the actual taxa. But we could vanish down a rabbit hole here... a bit like PSC we could have far more species, but in this case totally cryptic to our cognitive abilities. A world where everything was decided by the prick of a needle, would then result in a completely unworkable system for field observation.

 

[Jon.Bryant]

Many species which have been split e.g Cutia, do not respond to each other vocally, outside of their natural range and vocalisations do play a fairly large part these days in touted splits afaik.

But someone has to work out whether vocals are an important reason for separation of taxa or not. Would a Himalayan Cutia be sexually attracted to a Vietnamese Cutia? Perhaps not. But what about those annoying hybrids - it appears that Collared Flycatchers can be attracted to the songs of Pied Flycatchers (or vice versa), Pallid to Common Swift, Blyth's Reed to Reed, Herring Gull to Lesser Black-backed Gull, Wigeon to Chiloe Wigeon etc. etc. What then becomes of relevance, is how important is vocalization in maintaining general isolation, as opposed to other differences (say in morphology)... and we are back to Tobias.

 

[Andy Adcock]

But someone has to work out whether vocals are an important reason for separation of taxa or not. Would a Himalayan Cutia be sexually attracted to a Vietnamese Cutia? Perhaps not. But what about those annoying hybrids - it appears that Collared Flycatchers can be attracted to the songs of Pied Flycatchers (or vice versa), Pallid to Common Swift, Blyth's Reed to Reed, Herring Gull to Lesser Black-backed Gull, Wigeon to Chiloe Wigeon etc. etc. What then becomes of relevance, is how important is vocalization in maintaining general isolation, as opposed to other differences (say in morphology)... and we are back to Tobias.

NO......that's my point. I know people that have experimented with the calls and they do not respond so won't recognise the potential to mate. Aside from passerines, your others are not species which depend on vocalisations to attract a mate afaik, drakes will gang rape females to the point that they can drown.

 

[Thijsdekruif]

So yes, what appears the same to our cognitive abilities may be more distinct to the actual taxa. But we could vanish down a rabbit hole here... a bit like PSC we could have far more species, but in this case totally cryptic to our cognitive abilities. A world where everything was decided by the prick of a needle, would then result in a completely unworkable system for field observation.

Here you touch an essential point to me. Are we defining species for our lists? Or for science, to understand and be able to properly protect nature.
I'm for the last, even if it means cryptic species. And that might mean not being able to be certain what species you've seen (european vs. mediterranean storm-petrels). But quite often, we might find clues on how to determine these formerly cryptic species anyway.

 

[Thijsdekruif]

And birds do have a great sense of smell (at least some, like tubenoses and kiwis). There is so much we don't know.

 

[Jon.Bryant]

NO......that's my point. I know people that have experimented with the calls and they do not respond so won't recognise the potential to mate.

I wasn't saying the opposite.

I was however pointing out that hybridization occurs in other taxa that have very different vocals - say Blyth's and Eurasian Reed Warbler, so why? How important is vocalisation in pairing of Reed Warblers? Perhaps in Cutia's it is a definitive and Himalayan Cutia is never attracted to Vietanamese Cutia vocalizations. But, I would add you would need to do a hell of a lot of experimentation with a lot of different birds, to get even a 95% confidence limit of this fact?

The Cuttias can't hybridise because of non overlapping range, but obviously in Reed Warblers and Collared Flycatchers, sometimes the lack of attraction breaks down. So what proportion of Collared Flycatchers are attracted to Pied Flycatchers and why? - or to turn it on it's head, what keeps the species generally apart and stops them from normally hybridizing, a lack of attraction to each others vocals, looks or both? This is kind of what Tobias is all about, Collared and Pied Flycatchers are generally kept apart by X, Y and Z, so I can apply the same rules to say Atlas Flycatcher, which does not have an overlapping breeding range with Collared or Pied.

If vocals were the golden bullet, leading to thing always acting as separately species, we can't explain most hybrid events, and we would probably have to increase the number of species based on our existing knowledge of vocal differences between subspecies.

 

[Mysticete]

I think most lists nowadays use the Tobias system (BirdLife state they do). So take two birds of the same genus that come into contact but behave as separate 'species'. Next work out what is the likely reason they (largely) live separately and do not hybridize, then apply these findings to other taxa in the genus that do not come into contact with one another. We then have a weighted set of criteria on a genus by genus basis - thus getting over the problem as to why gulls act like separate species despite narrow genetic diversity etc. This just becomes a gulls 'thing'.

I actually think no one other than Birdlife does, and in fact thanks to Avilist they probably don't either. You could practically make a drinking game out of the number of times someone in a SACC criticizes the Tobias system in a SACC proposal. As a quick and dirty method of assessment it's fine, but you are still basically trying to fit continuous traits into a discrete system that doesn't take in account that different groups of birds may acrue meaningful morphological differences at different rates.

 

[Jon.Bryant]

that doesn't take in account that different groups of birds may acrue meaningful morphological differences at different rates.

I thought this was exactly what Tobias was about, or have I got the wrong end of the stick - different assessment criteria for different groups of birds.

Can you clarify?

 

[Jon.Bryant]

but you are still basically trying to fit continuous traits into a discrete system

Isn't that the same for all systems? As stated above isn't evolution analogue and taxonomy binary?

 

[Mysticete]

I thought this was exactly what Tobias was about, or have I got the wrong end of the stick - different assessment criteria for different groups of birds.

Can you clarify?

I may very well be mistaken since its been awhile since I delved into this, but I don't think they calibrated there system to different groups of birds. At least this paper doesn't list any step whereby they use a different total point difference for different groups of birds. There is at least one paper out there complaining about this, as cryptic species are likely to go undetected.

I should also mention that I am overall neutral on this. pretty much all systems have failings when it comes to evaluating when to split or lump. A lot of the Tobias splits have been backed up since the original publication. It's probably a case that a high score of 7 or provides strong support for a split, but a lower score doesn't necessarily imply that something shouldn't be split. It can be used to support a proposed split but not necessarily refute one.

 

[Mysticete]

Isn't that the same for all systems? As stated above isn't evolution analogue and taxonomy binary?

Yes, which is the inherent challenge of taxonomy. A lot of species just plain exist in a gray zone between species or subspecies, no matter the concept or criteria (I think Green-winged Teal is a good example of this). the decision on what to do then truly become arbitrary.

 

[Jon.Bryant]

I actually think no one other than Birdlife does, and in fact thanks to Avilist they probably don't either. You could practically make a drinking game out of the number of times someone in a SACC criticizes the Tobias system in a SACC proposal. As a quick and dirty method of assessment it's fine, but you are still basically trying to fit continuous traits into a discrete system that doesn't take in account that different groups of birds may acrue meaningful morphological differences at different rates.

The link before to the paper on assessment of Tobias states

'Species are fundamental to biology, conservation, and environmental legislation; yet, there is often disagreement on how and where species limits should be drawn. Even sophisticated molecular methods have limitations, particularly in the context of geographically isolated lineages or inadequate sampling of loci. With extinction rates rising, methods are needed to assess species limits rapidly but robustly. Tobias et al. devised a points-based system to compare phenotypic divergence between taxa against the level of divergence in sympatric species, establishing a threshold to guide taxonomic assessments at a global scale. The method has received a mixed reception. To evaluate its performance, we identified 397 novel taxonomic splits from 328 parent taxa made by application of the criteria (in 2014‒2016) and searched for subsequent publications investigating the same taxa with molecular and/or phenotypic data. Only 71 (18%) novel splits from 60 parent taxa have since been investigated by independent studies, suggesting that publication of splits underpinned by the criteria in 2014–2016 accelerated taxonomic decisions by at least 33 years. In the evaluated cases, independent analyses explicitly or implicitly supported species status in 62 (87.3%) of 71 splits, with the level of support increasing to 97.2% when excluding subsequent studies limited only to molecular data, and reaching 100% when the points-based criteria were applied using recommended sample sizes.'

...so it seems potentially accurate if used well.

I am now actually wondering if BirdLife use Tobias, as they profess (or Tobias+). The reaon I say this is because it appears that this paper seems to set aside Tobias from DNA sampling, whereas BirdLife frequently report that a species has not been split, because the level of genetic divergence is shallow. Can you have Tobias that includes DNA as one of the parameters in the point base system. This is why I thought we can 'accept' the shallow divergence in gulls but not say in cormorants.

 

[l_raty]

But I am not sure what we can conclude if we contrast and compare the results of current existing taxonomies - each decision 'hides' any dis-consenting votes, which we then compare with another decision that does the same - what does this prove or add?

If support for something is marginally above what is necessary to have it accepted, chances are that it will be below that threshold in one of the checklists. I agree it's far from optimal, though, and if the dissenting votes are equally scattered over the voting panels, something could be accepted despite significant dissent... But it's better than nothing.

To be frank, I'm actually far from convinced that voting can ever be an acceptable way to deal with a scientific question.

 

[Andy Adcock]

I actually think no one other than Birdlife does, and in fact thanks to Avilist they probably don't either. You could practically make a drinking game out of the number of times someone in a SACC criticizes the Tobias system in a SACC proposal. As a quick and dirty method of assessment it's fine, but you are still basically trying to fit continuous traits into a discrete system that doesn't take in account that different groups of birds may acrue meaningful morphological differences at different rates.

Nearly commented the same but wasn't sure if I was misremembering.

 

[Andy Adcock]

If support for something is marginally above what is necessary to have it accepted, chances are that it will be below that threshold in one of the checklists. I agree it's far from optimal, though, and if the dissenting votes are equally scattered over the voting panels, something could be accepted despite significant dissent... But it's better than nothing.

To be frank, I'm actually far from convinced that voting can ever be an acceptable way to deal with a scientific question.

My point exactly with the example of a 5/4 split of the nine man committee.