How do birders want species-definition to be determined? Via Morphology, assortative breeding, or DNA analysis? (1 Viewer)

[wolfbirder]

Increasingly we seem to be depending on the results of DNA-analysis looking for x % divergence to determine whether a species is truly different. Don't get me wrong, DNA analysis is crucial, and it often helps determining species-separation of indistinct 1st-winter birds like shrikes. So there is undoubtedly a key role for DNA analysis, in my view.

But it concerns me that we depend too much on DNA analysis 'at times'. Species may have separated to the point where they breed sympatrically but don't yet have the required % DNA-divergence, which might take many hundreds or thousands of years. I totally acknowledge that I have very limited understanding of DNA. In my simple thinking though , surely, birds know if they are different before science necessarily realises the same? The Redpolls and Crossbills complex are possibly classic examples of this. Furthermore, if we can see morphological differences with the human eye, and critically, if assortative breeding exists, surely they should be respected as different species?

So I a guess I am asking whether we want a scientific assessment based on DNA, or do we want a more-simplistic morphological-difference assessment, especially where they are breeding as different species anyway? I know its probably not as simplistic as I make out here, but personally, it concerns me that we are increasingly relying too much on DNA to make such decisions, its not what I personally want, but as I have often discovered, I may well be in the minority here.

Thoughts.....................

 

[Welsh Peregrine]

I am generally in favour of an integrated approach using all available lines of evidence. This makes most biological sense to me, but means that there will be plenty of borderline cases (there is clearly not a magic moment when speciation occurs). However, I could be persuaded that there might be a rationale for using a specific definition to decide such contentious cases consistently (while accepting it will be an artificial test).

 

[Mysticete]

Increasingly we seem to be depending on the results of DNA-analysis looking for x % divergence to determine whether a species is truly different. Don't get me wrong, DNA analysis is crucial, and it often helps determining species-separation of indistinct 1st-winter birds like shrikes. So there is undoubtedly a key role for DNA analysis, in my view.

But it concerns me that we depend too much on DNA analysis 'at times'. Species may have separated to the point where they breed sympatrically but don't yet have the required % DNA-divergence, which might take many hundreds or thousands of years. I totally acknowledge that I have very limited understanding of DNA. In my simple thinking though , surely, birds know if they are different before science necessarily realises the same? The Redpolls and Crossbills complex are possibly classic examples of this. Furthermore, if we can see morphological differences with the human eye, and critically, if assortative breeding exists, surely they should be respected as different species?

So I a guess I am asking whether we want a scientific assessment based on DNA, or do we want a more-simplistic morphological-difference assessment, especially where they are breeding as different species anyway? I know its probably not as simplistic as I make out here, but personally, it concerns me that we are increasingly relying too much on DNA to make such decisions, its not what I personally want, but as I have often discovered, I may well be in the minority here.

Thoughts.....................

It's not an either/or situation most of the time in birds. Generally genetic differences correspond to known morphological differences. It's just a matter often of how "different" something needs to be to be recognized as a species.

And what other criteria are in play. The biological species concept is still the dominant concept in ornithology used, which basically asks how/if two populations are reproductively isolated from one another. Morphological and genetic differences are just a proxy for reproductive isolation. For the most part, species that may be reproductively isolated and cryptic in morphology and voice are pretty rare in birds, effectively just some finch-like species and some seabirds.

 

[Andy Adcock]

I am generally in favour of an integrated approach using all available lines of evidence. This makes most biological sense to me, but means that there will be plenty of borderline cases (there is clearly not a magic moment when speciation occurs). However, I could be persuaded that there might be a rationale for using a specific definition to decide such contentious cases consistently (while accepting it will be an artificial test).

This, however if a 'species' is only identifiable using DNA, then away from known range, if it's impossible to ID in the field, splitting is largely irrelevent to the field birder?

 

[Andy Adcock]

It's not an either/or situation most of the time in birds. Generally genetic differences correspond to known morphological differences. It's just a matter often of how "different" something needs to be to be recognized as a species.

And what other criteria are in play. The biological species concept is still the dominant concept in ornithology used, which basically asks how/if two populations are reproductively isolated from one another. Morphological and genetic differences are just a proxy for reproductive isolation. For the most part, species that may be reproductively isolated and cryptic in morphology and voice are pretty rare in birds, effectively just some finch-like species and some seabirds.

Really?
I see more and more evidence of so called 'field guide taxonomy' where e.g vocalisations, geographical isolation and habitat preference are the main factors employed? I think, but stand ready to be corrected, that many of the splits in HBW are not done using the BSC?

 

[Welsh Peregrine]

This, however if a 'species' is only identifiable using DNA, then away from known range, if it's impossible to ID in the field, splitting is largely irrelevent to the field birder?

As a Biologist, I am happy to accept that there are real species (entities with distinct genomes, niches and reproductive traits) which are not always distinguishable in the field. However, as a listing naturalist, I will try to allocate names (labels) to sightings. Unless these sightings are being used in some scientific way, eg to affect conservation measures, then my likely errors affect nothing more than my own lists.

 

[Mysticete]

Really?
I see more and more evidence of so called 'field guide taxonomy' where e.g vocalisations, geographical isolation and habitat preference are the main factors employed? I think, but stand ready to be corrected, that many of the splits in HBW are not done using the BSC?

Those criteria you mention all go back to to reproductive isolation however in some way or another.

Innate vocalizations, especially in song, are crucially important in species recognition (hence playback experiments often used as arguments in species debates).

I haven't seen either geographic isolation or habitat preferences used as the MAIN criteria for most bird species splits. Rather those characteristics are used as either an additional line of evidence or a complicating factor to assessing speciation. Since allopatric and sedentary populations are not likely to often come into contact, there is usually inference that some unique characteristics possessed by each population would either limit interbreeding or make the resulting offspring less viable. Or if the genetic divergence is significant enough, it might suggest that both population have been isolated so long that reproductive isolation in some manner has to be relevant.

Field Guide Taxonomy is less "a species concept", and more reflects that species exist on a continuum, and there is always some subjectivity when making a call. In this specific case, the authors are more splitters and are willing to make a call on taxonomy based on their own experience, leaning towards splitting populations that maybe haven't had the degree of published work necessary to convince more conservative folks that a split is warranted.

 

[Mysticete]

This, however if a 'species' is only identifiable using DNA, then away from known range, if it's impossible to ID in the field, splitting is largely irrelevent to the field birder?

Are their many birds that fall into this category? About the only ones I can think of are some seabirds like storm petrels or prions. Even then I have seen folks argue identification based on things such as molt patterns and so on. Crossbills should they be split could potentially be tough, but there are call note differences, even if they are subtle.

 

[Andy Adcock]

Are their many birds that fall into this category? About the only ones I can think of are some seabirds like storm petrels or prions. Even then I have seen folks argue identification based on things such as molt patterns and so on. Crossbills should they be split could potentially be tough, but there are call note differences, even if they are subtle.

Stonechats can be tough which leads to a scramble for excrement when a putitive rare one turns up here. Not sure how easy Eastern and Western Olivaceous Warblers are and there must be plenty of others.

 

[Xenospiza]

Stonechats can be tough which leads to a scramble for excrement when a putitive rare one turns up here. Not sure how easy Eastern and Western Olivaceous Warblers are and there must be plenty of others.

But birds that "look like" stejnegeri now pretty much invariably turn out to be just that.
Western and Eastern Olivaceous Warbler can be differentiated in the field by e.g. the colour of the lores (light vs. dark), tail pumping (yes vs. no), bill width and colour (both probably harder in the field); if I could do this is another question...

Although I am not a fan of splits that lead to an array of similar-looking and -sounding birds, in some cases DNA can help to find differences in plumage and behaviour that we did not note before.

 

[DMW]

But birds that "look like" stejnegeri now pretty much invariably turn out to be just that.
Western and Eastern Olivaceous Warbler can be differentiated in the field by e.g. the colour of the lores (light vs. dark), tail pumping (yes vs. no), bill width and colour (both probably harder in the field); if I could do this is another question...

Although I am not a fan of splits that lead to an array of similar-looking and -sounding birds, in some cases DNA can help to find differences in plumage and behaviour that we did not note before.

Isn't this why we have the concept of the sub-species in the BSC? In modern times, there are relatively few genuinely novel bird species described but a whole plethora of sub-species elevated to species rank. There seems to be a Muller's Ratchet of ever-decreasing thresholds for species level units. As birders, at least, would we be better-off turning the clock back a bit and expecting species to have significant phenotypic differences, for listing purposes at least? Frankly, I have limited interest in chasing every drongo or Red-bellied Pitta, and was much happier when they could be safely ignored as sub-species!

 

[Xenospiza]

Isn't this why we have the concept of the sub-species in the BSC? In modern times, there are relatively few genuinely novel bird species described but a whole plethora of sub-species elevated to species rank. There seems to be a Muller's Ratchet of ever-decreasing thresholds for species level units. As birders, at least, would we be better-off turning the clock back a bit and expecting species to have significant phenotypic differences, for listing purposes at least? Frankly, I have limited interest in chasing every drongo or Red-bellied Pitta, and was much happier when they could be safely ignored as sub-species!

Haha, I also had that pitta in mind! Minute differences in plumage, sounds the same everywhere...

 

[Mysticete]

Isn't this why we have the concept of the sub-species in the BSC? In modern times, there are relatively few genuinely novel bird species described but a whole plethora of sub-species elevated to species rank. There seems to be a Muller's Ratchet of ever-decreasing thresholds for species level units. As birders, at least, would we be better-off turning the clock back a bit and expecting species to have significant phenotypic differences, for listing purposes at least? Frankly, I have limited interest in chasing every drongo or Red-bellied Pitta, and was much happier when they could be safely ignored as sub-species!

I mean you don't HAVE to go an look for those birds. The IOC isn't going to break down your door if for your own personal list you don't recognize a split.

Much like everything else in science, these splits are a result of having new methods and closer scrutiny to taxa over the last few decades than in prior years. Lack of recognition of a given split isn't necessarily the result of finer parsing, it's more often simply a result of lack of information, and in many cases simply reverses past decisions which were often arbitrary.

 

[James Lowther]

I mean you don't HAVE to go an look for those birds. The IOC isn't going to break down your door if for your own personal list you don't recognize a split.

Much like everything else in science, these splits are a result of having new methods and closer scrutiny to taxa over the last few decades than in prior years. Lack of recognition of a given split isn't necessarily the result of finer parsing, it's more often simply a result of lack of information, and in many cases simply reverses past decisions which were often arbitrary.

Agree,
The solution is not for birders to demand a different approach to delineation of species, but to take a different approach to ticks. In other taxonomic groups, mammals, insects, plants etc people seem much more content to list spp and agg etc.
Cheers
James

 

[DMW]

Agree,
The solution is not for birders to demand a different approach to delineation of species, but to take a different approach to ticks. In other taxonomic groups, mammals, insects, plants etc people seem much more content to list spp and agg etc.
Cheers
James

Well, in practical terms that pretty much amounts to the same thing, doesn't it? Let's say I set up the global 10,000 club and decide that we will only recognise one species of northern hemisphere Soft-plumaged Petrel for listing purposes, with Fea's, Desertas and Zino's treated as sub-species: that's really no different in practical terms from calling it Soft-plumaged Petrel Agg, is it? There's no objective test that makes these Pterodromas species or sub-species, just different opinions or interpretations of facts. From a birder's perspective, it means you can tick a distant petrel half a mile out, rather than have a frustrating "Fea's-type petrel".

 

[DMW]

I mean you don't HAVE to go an look for those birds. The IOC isn't going to break down your door if for your own personal list you don't recognize a split.

Much like everything else in science, these splits are a result of having new methods and closer scrutiny to taxa over the last few decades than in prior years. Lack of recognition of a given split isn't necessarily the result of finer parsing, it's more often simply a result of lack of information, and in many cases simply reverses past decisions which were often arbitrary.

Oh, thanks for that, I actually thought they did.

 

[James Lowther]

Well, in practical terms that pretty much amounts to the same thing, doesn't it? Let's say I set up the global 10,000 club and decide that we will only recognise one species of northern hemisphere Soft-plumaged Petrel for listing purposes, with Fea's, Desertas and Zino's treated as sub-species: that's really no different in practical terms from calling it Soft-plumaged Petrel Agg, is it? There's no objective test that makes these Pterodromas species or sub-species, just different opinions or interpretations of facts. From a birder's perspective, it means you can tick a distant petrel half a mile out, rather than have a frustrating "Fea's-type petrel".

Well, on the specifics, putting aside the Fea’s/Desertas split Zino’s and Desertas are clearly good biological species and can be identified fairly straightforwardly from boats close to the breeding areas so who cares if birders struggle to distinguish them when sea watching from remote headlands?
On the generic side I don’t think anyone is stopping birders coming up with a list of tickable taxa if they want to. We all know the high regard the UK400 list is held in after all.
The practical difference between the agg spp approach and the birders’ species list approach is that the first acknowledges that the species is a real biological concept and also that under some circumstances it may be possible to distinguish between different species in the group so you may even be able to upgrade your tick or add extra members of the group to your list. The second merely pretends that species don’t exist beyond what it’s easy for birders to ID.
Cheers
James

 

[Mysticete]

On the generic side I don’t think anyone is stopping birders coming up with a list of tickable taxa if they want to. We all know the high regard the UK400 list is held in after all.
The practical difference between the agg spp approach and the birders’ species list approach is that the first acknowledges that the species is a real biological concept and also that under some circumstances it may be possible to distinguish between different species in the group so you may even be able to upgrade your tick or add extra members of the group to your list. The second merely pretends that species don’t exist beyond what it’s easy for birders to ID.
Cheers
James

I would agree with James. Species are something that that as a concept exists in science and really shouldn't be geared towards birders, but whether the facts support species recognition under whatever concept the researchers or taxonomic committee adhere to.

I think a list of field diagnosable taxa isn't a horrible idea, but I'm not certain it would solve the root of the issues here, that a lot of birders hate uncertainty. Plus, "diagnosable taxa" is kind of arbitrary and really comes down to individual birders skill. I certainly know people who have zero problem identifying Red Crossbill call types, where most folks including myself would struggle. So you would probably still have a situation where there would be birds that you couldn't narrow down to a specific form.

 

[ZanderII]

Well, in practical terms that pretty much amounts to the same thing, doesn't it? Let's say I set up the global 10,000 club and decide that we will only recognise one species of northern hemisphere Soft-plumaged Petrel for listing purposes, with Fea's, Desertas and Zino's treated as sub-species: that's really no different in practical terms from calling it Soft-plumaged Petrel Agg, is it? There's no objective test that makes these Pterodromas species or sub-species, just different opinions or interpretations of facts. From a birder's perspective, it means you can tick a distant petrel half a mile out, rather than have a frustrating "Fea's-type petrel".

Given that logic it maybe best to lump all 'jaegers' too as these are routinely misidentified on seawatches (and even when sat on reservoirs inland), then you can just tick 'Jaeger' or 'Small Skua'. One problem with this taxonomic concept is the historical geneflow between Pomarine and the 'Catharacta' group. However given that all these species are hard to identify and given ongoing geneflow it would probably be best to lump all species of larger skuas and smaller jaegers together as a single species.

 

[Welsh Peregrine]

And “Gull”, and “Duck” and...😉