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Old Friday 24th September 2010, 13:33   #26
Kirk Roth
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Originally Posted by lewis20126 View Post
Is this necessarily the case with all animals? - certainly not the case with the use of the "subspecies" concept in plants.

cheers, alan
It certainly is the case!! I believe you are thinking of plant varieties, which do not (necessarily) have a geographic component.

To illustrate with a popular example, Cannabis sativa has several subspecies, depending on the authority. C. s. sativa is the northern subspecies is the northern form, preferred for hemp rope, while C. s. indica is the southern subspecies... cherished for other purposes.

C. s. sativa can be further subdivided into two varieties: C. s. sativa var. sativa may grow tall and has relatively low resin levels. C. s. sativa var. spontanea is shorter and bushier. I'll not get into all the varieties of indica! But these varieties, while having a strong genetic component, are not necessarily geographically divergent, although each may fare better in specific microhabitats.

But the point is that the botanical community has, for over a century, had a system for genetic but nongeographical variation - perhaps ornithologists should become more comfortable with this as well.

I feel that there is a good case for some biological species within the Red Crossbill complex, but at our current level of understanding and for those "taxa" that may not yet have achieved species definition, I feel that we are dealing with different "varieties" of crossbills, not subspecies.
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Old Friday 24th September 2010, 13:54   #27
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Plant taxonomy

I'm completely ignorant of plant taxonomy, but I noticed this story in the Guardian a few days ago:
http://www.guardian.co.uk/science/20...rld-plant-list

Not sure if it's referring to synonyms for specific names, subspecies, varieties...

Richard (sorry, wandering off topic!)
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Old Friday 24th September 2010, 14:00   #28
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I do appreciate all that. However, with finches, there is well documented geographical variation in plumage which you can compare to vocal variation. For crossbills, there are studies showing some average (i.e. not diagnosable) differences in bill size or shape but not much more.
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And yes, finches are famous for learning sounds - also to learn and change songs during life. I would expect experiments when captive crossbills were housed for several years with different call types, or in presence of recordings, and they kept their calls.
??? I'm confused by these comments. You guys do realize that crossbills ARE finches?

I would have the opposite expectation in the proposed experiment - that crossbills learn their songs just like other finches. However, your result would be more interesting, and would lend evidence that perhaps call note specificity had developed for the benefit of crossbills to tell the difference between good and bad potential mates.

Which brings me around again to the point I was trying to make above, but apparently failed at: species are defined by who breeds with whom, not who sounds like whom. Frankly, I wouldn't care what sounds crossbills make, except that there seems to be a correlation between exclusive breeding populations and variability in calls. But the populations are important here, and whether they tell each other apart by plumage, call type, smell, or ESP, it shouldn't matter so long as the differentiation is real.

And while I'm at it, I think its an exaggeration to suggest that the call types can only be distinguished by an elite few researchers. I can only speak for the American birds, but upslurs vs. downslurs vs. even notes are fairly easy to distinguish. The highness vs. lowness seems a bit less easy to my untrained ears, but not impossible. And some, such as the Type 4, are quite distinctive. Here in the eastern U.S., I've heard Types 1, 2, and 4, and these are distinguishable. And I'm no Loxiologist by any means...
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Old Friday 24th September 2010, 15:42   #29
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There was a typo on one of the emails above which seems to have been propagated. For "finch" read "chickadee" or "tit".

I suppose my point is, if voice is learned, there are no genetic differences and no morphological differences between populations, then how are humans deciding which populations are or are not interbreeding with which other populations? And how do we not know that any observed non-interbreeding is maintained by preferences for "social groupings" rather than incapacity to interbreed and produce fertile offspring? (Maybe this discussion also then goes on to species debates and splitters vs. lumpers which there is plenty of material on already elsewhere.)

I would not want to respond on the other points, as I agree with the last posting. Some of the papers concerning the geographical variation in different calls of these birds based on studies of the European forms are also quite convincing.
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Old Friday 24th September 2010, 15:54   #30
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I think it's been said before on a similar thread, but it really doesn't matter how easily humans can identify a species, it only matters how well the bird itself can

Although I agree that much more work needs to be done before I would feel comfortable labeling the different types as different species.

Also I am not aware of any subspecies which have non fixed distributions during the breeding season. Of course, in winter there is plenty of mixing.
Personally I think that the only question in the Crossbill species debate is "where exactly do we draw the line when defining two separate species?".

There is one very good example of a species that has 'sub groups' with clearly different vocalisations, and which can now be found co-habiting the same areas throughout the year - often with very limited interbreeding between the different 'groups'.
I realise that it is generally considered 'politically incorrect' to even suggest that the same subspecies/race concept that we apply to other animals can be applied to humans (I think partly because the term 'subspecies' can be taken as an implication that one or more races are 'below' others), but I do think that comparisons can be made.

So the crossbill scenario (as I understand it) is that there are groups that can be separated by different vocalisations but (in most cases) have been found to be practically indistinguishable genetically, and physical differences are so slight that they are of no practical use. The idea that these should be treated as different species is apparently supported by the fact that they can be found breeding in the same areas with limited interbreeding between groups with different vocalisations.

The human comparison: There are groups that can be separated by vocalisations (I can recognise several languages even though I may not understand them, and there are easily distinguished regional differences even within a country). Genetic differences are apparently slight, but physical differences can sometimes be obvious - although not necessarily linked to differences in vocalisation. Finally (and this may be disputed by some), although humans from all parts of the world can be found in the same cities, there is relatively little interbreeding between groups with different vocalisations (languages). I doubt that anyone can disagree that wherever there are immigrants into a country, communities of people with the language and culture become established. There is obviously some degree of mixing between people from different countries, but I think that it is fair to say that this is clearly restricted if one person does not speak the language understood by the other.

Returning to the crossbills - perhaps there is mixing, and interbreeding, between different 'vocal groups'. If this were the case, surely it would be most likely when a bird from one group learnt the calls/song used by another group and then started using these when associating with birds that use these different calls? Exactly the same as humans learning, and using, another language to allow them to communicate and mix with another group.

It may well be that crossbills are best treated as a number of different species, personally though I'm yet to be convinced, and until a lot more research is available I think that it is better to be conservative with regard to the number of species (I'm not even convinced that Scottish Crossbill is really a valid species!).
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Old Friday 24th September 2010, 17:41   #31
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I suppose my point is, if voice is learned, there are no genetic differences and no morphological differences between populations, then how are humans deciding which populations are or are not interbreeding with which other populations?
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So the crossbill scenario (as I understand it) is that there are groups that can be separated by different vocalisations but (in most cases) have been found to be practically indistinguishable genetically, and physical differences are so slight that they are of no practical use.
Please read some of the articles listed above, or here:

http://www.birdforum.net/showthread....ght=crossbills

There are morphological differences. Granted, these "ornithologists' differences" and not "birders' differences," but they are statistically significant and consistently found. Otherwise... why would this body of research even exist?

I'm sure I'd agree that if the ONLY thing different about these birds were their voices, it would be a fairly minor distinction, but that simply isn't true.
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Old Friday 24th September 2010, 21:54   #32
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I have read all these papers.

Let's look at the Condor "new species" description from last year.

Diagnosis: "Very similar to other Red Crossbills in North America but larger (body mass and bill depth, but upper mandible relatively short) on average than other Red Crossbills currently found commonly north of Mexico (Table 1) and with distinctive vocalizations (see below; Smith and Benkman 2007). As in other Red Crossbills, males are reddish in body coloration whereas females are greenish-gray and smaller than males (Table 1; see below)."

Conclusion:
Voice - different, but see above discussion.
Plumage - the same.
Biometrics - "average differences" - i.e. not diagnosable. If you look at the table of biometric data in the paper, you can see some highly unimpressive divergence in biometrics. Data on range of measurements for males for the variables mentioned in the species diagnosis section is below:

Mass:
Type 2 28.8–38.6
Type 5 28.6–38.6
New species 29.2–39.4

Bill depth:
Type 2: 8.97–10.38
Type 5: 8.77–10.14
New species: 9.05–10.56

Bill length from nostril:
Type 2: 13.79–18.87
Type 5: 13.95–16.87
New species: 13.40–17.30

These are not diagnostic differences. With enough data, one might be able to generate a positive t-test, showing statistically significant average differences, but based on these sorts of data you would expect at least 80-90% of individuals not to be capable of being identified based on biometrics.

Which takes me back to the original posting. If voice is all there is to go on in terms of real diagnosable differences, and this can shift, who is to say this is not a learned character?

The paper states: "We found one instance of a female of call type 2 shifting its call to match that of its mate, a South Hills Crossbill, in successive years, but because this shift occurred only in the year following this pair’s successful breeding such call shifts should affect our estimates of the frequency of hybridization only minimally (Keenan and Benkman 2008; see also Summers et al. 2007)." That is one possible interpretation but one could see people arguing for others in terms of delimiting species based on (i) actual observed hybridisation between "species"; and (ii) learning by one "species" of the other "species" voice.

Going back again to the original posting, I do think this and other papers make up a fantastic piece of research but it seems a bit premature to be describing sympatric "species" without diagnosable differences except for in characters that may be learned. AOU's NACC seemed to have a similar view.
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Old Saturday 25th September 2010, 00:31   #33
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It's A Crossbill Jim, but not as we know it.

I can do all the UK occuring loxia calls by ear. Do I get a prize ? Sonagrams show the finer details and variations between "types" which may partly be responsible in taking the splitting madness too far. I prefer to use my ear first, then sonagram to catalogue the call.

Scottish Crossbill does exist, it's just that it might not be the one you think it is.....or there might be more than one !

Some pretty earth shattering stuff re- Scottish Crossbill calls in the pipeline. Keep tuned to Loxia Fantastica for updates.
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Old Tuesday 28th September 2010, 06:37   #34
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I am a tad surprised at the discussion on learned vocalizations. Fringillids are well known to learn song, not only that they learn calls which is highly unusual in passerines. On the other hand they do some weird stuff like call matching between pairs, and seem to sort each other out into single call type flocks based on these learned calls. It is complex, and this is why crossbills have not been a shoo-in for consideration as different species. The calls are learned but at the same time they are used for identification/segregation of groups, this tendency to mix with those of your own call type may be culturally facilitating specialization. The problem is that you need only a few to mix with the wrong gang in populations to keep gene flow alive.
To get a handle on the crossbill issue it would be good to study some other related finches that show geographic variation in call type. Three in North America are Pine Grosbeak, Evening Grosbeak, and Purple Finch....I wouldn't be surprised if Pine Siskin also fits the bill (ahem). The three mentioned above have identifiable call type differences but they stay within their own separate geographic areas, at least most of the time. It would be interesting to do molecular as well as vocal playback work on these simpler systems to understand fully the role of call type in differentiation. Then these results can be applied to better understand or resolve which populations or call types in the Red Crossbill could in fact have reached species thresholds, versus some NEW type of within species variation that is yet unnamed (subspecies does not work in this case as noted above). Alvaro.
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Old Tuesday 28th September 2010, 10:17   #35
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Per Evening Grosbeak, vocalization and morphology matching (if not molecular) Earbirding has a timely post:
http://earbirding.com/blog/
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Old Tuesday 28th September 2010, 10:59   #36
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Evening Grosbeak

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Originally Posted by mb1848 View Post
Per Evening Grosbeak, vocalization and morphology matching (if not molecular) Earbirding has a timely post:
http://earbirding.com/blog/
Re the potential reinstatement of Grinnell's five subspecies, Gillihan & Byers 2001 (BNA Online) mentions six:
  • vespertinus
  • brooksi (incl californicus, warreni)
  • montanus (incl mexicanus)
Which five did Grinnell recognise?

Richard
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Old Tuesday 28th September 2010, 14:10   #37
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Biometrics - "average differences" - i.e. not diagnosable.
All the quoted biometrics are statistically significant, which (to a scientist) is what defines a "real" difference. If your argument is with the overlap in morphology of a minority of individuals in a museum tray, than I guess the issue is with statistics rather than biology - and frankly I'm too tired to argue about that! I'll end by maintaining 1) that overlapping morphology is a problem with several plant species (Solidago, and other composites, especially), some flies, and probably many others. And that is without getting into Hugh Patterson's "Recognition Species" concept. In a taxa with such complex behavior as birds, I'd be amazed if they are exempt from this sort of crypsis. and 2) I still maintain that breeding behavior, not morphology, is a better basis for species, (or "Type") definition.

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To get a handle on the crossbill issue it would be good to study some other related finches that show geographic variation in call type. Three in North America are Pine Grosbeak, Evening Grosbeak, and Purple Finch
Very good idea. To be more challenging, I'd add redpolls to the list. However, I'd caution that one key aspect of crossbill biology and the assumed driver of population differentiation is a specialized and ephemeral food source. All of our other finches seem to be moderately general feeders (okay, compared to crossbills anyway). But they would be very good models for vocalization studies.

I don't suppose there are any good data regarding Hispaniolan vs. Two-barred Crossbill vocalizations? While those have more geographic isolation, I'd wonder if vocalizations vary in a similar way to Red Crossbills.
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Old Tuesday 28th September 2010, 15:29   #38
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Originally Posted by Kirk Roth View Post
All the quoted biometrics are statistically significant, which (to a scientist) is what defines a "real" difference. If your argument is with the overlap in morphology of a minority of individuals in a museum tray, than I guess the issue is with statistics rather than biology - and frankly I'm too tired to argue about that! I'll end by maintaining 1) that overlapping morphology is a problem with several plant species (Solidago, and other composites, especially), some flies, and probably many others. And that is without getting into Hugh Patterson's "Recognition Species" concept. In a taxa with such complex behavior as birds, I'd be amazed if they are exempt from this sort of crypsis. and 2) I still maintain that breeding behavior, not morphology, is a better basis for species, (or "Type") definition.
In all fairness, the data presented in the above post included some examples, such as :
Quote:
Bill depth:
Type 2: 8.97–10.38
Type 5: 8.77–10.14
New species: 9.05–10.56
With these differences, it would be more than half of the birds that would not be diagnosable by bill depth (I think). In the monograph on subspecies that we had a long thread about earlier, one or more of the authors argued that if two populations differ by some few percent in one average measure, then you just had to increase the sample size enough and you would end up with a significant statistical difference that would not be biologically meaningful. As I understand it, that is the cause for the statistics called diagnisability which basically measures how large a percentage of the population cannot be id'ed to that population by whatever measure is used.

However, I do agree that the most important thing is to look at whether the birds themselves think that another bird belongs to the same species or not; the problem is to be able to ask the birds that question and be able to understand the answer

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Old Tuesday 28th September 2010, 15:32   #39
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All the quoted biometrics are statistically significant, which (to a scientist) is what defines a "real" difference. If your argument is with the overlap in morphology of a minority of individuals in a museum tray, than I guess the issue is with statistics rather than biology - and frankly I'm too tired to argue about that! I'll end by maintaining 1) that overlapping morphology is a problem with several plant species (Solidago, and other composites, especially), some flies, and probably many others. And that is without getting into Hugh Patterson's "Recognition Species" concept. In a taxa with such complex behavior as birds, I'd be amazed if they are exempt from this sort of crypsis. and 2) I still maintain that breeding behavior, not morphology, is a better basis for species, (or "Type") definition.
Sure but with overlap of about 80-90% in all 3 measurements it becomes useless in everything but the extremes. Under what theory are measurements with an overlap like that 'statistically significant' to the level that they are an argument for different species? It's fine when there are other strong arguments (like in the tapaculos Thomas Donegan has worked with) but if I understand this right there aren't yet for the crossbills. The voices are perhaps learned in them and the describers mention that they have observed voice shifts. If this is the case the breeding behavior can change. A crossbill with medium measurements could be one 'species' in one years. Shift voice and be another 'species' in another year. The genetic difference they reported in the description of the new crossbill is not impressive. Perhaps the South Hills Crossbill is a species but to my eyes evidence that can't be questioned is presently missing.

This is about birds and the established requirements for taxonomy of other groups are often different and this make them irrelevant to the discussion. The possibility of asexual reproduction in plants alone make any direct comparison with birds impossible.
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Old Wednesday 29th September 2010, 11:23   #40
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Originally Posted by Kirk Roth View Post
All the quoted biometrics are statistically significant, which (to a scientist) is what defines a "real" difference. If your argument is with the overlap in morphology of a minority of individuals in a museum tray, than I guess the issue is with statistics rather than biology - and frankly I'm too tired to argue about that!
I agree that science is all about measuring and quantifying differences, but I am not a fan of describing Crossbill species solely on "mean" bill depths, due to the massive variation or "range" of depths that can be present - birds in the overlap could potentially be of several types. Certainly here in Scotland the "overlap" is not restricted to a minority of specimens, quite the opposte ! In fact the overlap can be pretty extensive both sides of the mean which is what causes the problems with Common, Scottish and Parrot Crossbill. If you use calls to diagnose 'speciation' then you have some Parrot Crossbills with minimum bill depths of 11.9mm, well within the range of Scottish Crossbill. If you hadn't used a call, then it would probably be Scottish on historical and published biometrics.

My position is that data sets and slide rules are not the best components of Crossbill 'speciation' (if they are even species). Let's call it 'classification' - that would be cultural aspects (calls), breeding behaviour and ecological factors (where they are found, what they feed on etc) with biometric data factored in, though I don't think the 'minimum bill depth is a brilliant measurement of bill 'fitness' from my experience in Scotland.

Another thing - a Crossbill 'type' may be specialized to feed on a particular cone/seed, but that doesn't mean it can't survive on others....and whi ch is why a given population has variation in the first place.

THIS http://pinemuncher.blogspot.com/2009/09/thats-life.htmldiscussed the 'Scottish problem' and natural variation in that population a year ago with similar content to what is being discussed on here.
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Old Wednesday 29th September 2010, 18:49   #41
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Statistics

There was an interesting reference above to a recent paper on Tapaculos by Jorge Avendano and I by RoyN above:
PDF on the journal's website:
http://www.ornitologiacolombiana.org...nyavendano.pdf

I've also looked into variation in Grallaricula antpittas and some other groups, forthcoming:
Unauthorised online PDF of Grallaricula paper:
http://www.scricciolo.com/Nuovo_Neor...%20Donegan.pdf

This series of papers examine geographical variation in vocal, biometric and plumage characters in various Andean birds, assessing diagnosability of populations against the following tests:
1. Statistically significant differences (i.e. t-test, or other similar tests which compare averages for non-normally distributed)
2. 50% diagnosability (an old subspecies test: at least 50% of a population can be reliably identified from the other.
3. 75% diagnosability (the traditional subspecies test: at least 75% of a population can be reliably identified from the other).
4. No observed overlap in variables.
5. 97.5% (=close to 100% as anyone would sanely want to get) diagnosability. Phylogenetic species or modern subspecies concept.

The full details of calculations are set out in the paper.

First, it's notable how many times two populations will pass the "statistical significance" test but not even 50% of individuals are diagnosable (see data in the appendices of these two papers). Generally, biologists have been reluctant to describe populations even as subspecies when they show statistically significant but not diagnosable differences. Sure, they are different and this is demonstrated through the wonder of statistics (using the ecologist's love-child, the t-test), but that does not mean that you have to put a name on these populations. Under most species and subspecies concepts, it would be bad practice to do so based just on t-tests.

Secondly, I'm all in favour of birds which are diagnosable only by voice being described as subspecies or species, in groups where voice is innate (e.g. suboscines). See Grallaricula nana hallsi and G. n. nanitaea, in the paper mentioned above, which are mutually fully diagnosable by acoustic frequency of their songs but only show only non-diagnosable-but-significant-and-much-more-so-than-crossbills-differences in biometrics and plumage. (Also, another subspecies G n nana sits in the range in between them.) Where vocal characters studied are likely to be innate due to physiology (e.g. song speed, acoustic frequency range) this should be good enough for oscines too.

That takes me back to the first posting in this chain - and the need for young-rearing experiments to see if any of these differences in crossbill song may be constrained physically, eg. the ability of a bird to trill at certain speeds or reach certain acoustic frequencies. Crossbills, as I see it, reach level 4/5 in song, but that is assumed a learned character until more data is provided. In innate variables (e.g. biometrics) they reach only level 1 at best, and the differences in observed measurements are highly unimpressive.

If you compare the situation in crossbills to our 2008 tapaculos paper (and ignore characters not known/widely accepted to be innate), it would be effectively the equivalent of us having described all of the following as different species in Scytalopus spillmanni:
- west slope Ecuador population
- east slope Ecuador population
- West Andes Colombia population
- Central Andes Colombia population
- East Andes Colombia population.

We also described, but did not name, 4 other populations which are certainly subspecies under all concepts and species under many concepts (Perija population of "griseicollis", Tama population of "griseicollis", a Merida population of Scytalopus cf "spillmanni", Yariguies population of "rodriguezi") in that paper.

The S spillmanni populations all show "level 1" or more differences in voice or biometrics. Various of these are allopatric populations, with statistically significant vocal or biometric differences. But they are not species under a vast majority of concepts, and most of them are not even subspecies under several definitions. As a result, we did not describe any of these populations as even subspecies. (The East Andes Colombia population has much darker plumage, shorter biometrics, lower mass and notable mtDNA differences from other populations but there was a collecting gap in the specimen record which caused us to hesitate there.) This paper was published in a poorly read local journal (Ornitologia Colombiana).

We should have described 6 species in S spillmanni and got the paper published in Condor instead ... well, actually that would not have been a good idea at all.

I often get frustrated that people get so het up about others suggesting any kind of change to taxonomic treatments (e.g. AOU SACC's extreme approach to maintaining Peters and other status quo treatments). I would therefore apologise to the authors of the crossbills paper for getting on their back in this exchange. They have published a really great paper documenting a very interesting instance of geographical variation. However, it is unclear whether the time is right to be describing species-level taxa. (I could buy the new crossbill being a subspecies based on the information they provided although it would not have reached our "level 5" test for innate variables, so I would not have done so myself.) Describing geographical variation is an important exercise. It is best often to leave things at that and exercise restraint at the next step - naming - given that everyone has a different idea of what a species is. That is especially the case in instances like this where followers of many species concepts would not agree with the approach being taken.
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Old Wednesday 29th September 2010, 18:49   #42
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Old Wednesday 29th September 2010, 19:27   #43
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There are some interesting views raised in this thread, and in the links that have been posted. It is certainly an area that warrants further study in all species mentioned, but particularly in Crossbills where there may be sympatric speciation taking place. As to whether or not there are currently more species of Crossbill that should be recognised (or perhaps less species), it is obviously possible to argue the point from both sides. IMO a lot more needs to be known before we can really come to any conclusions about whether Crossbills of different call types & bill sizes really recognise each other as different species. If call types are the only way we can really tell them apart (because of overlap in measurements etc - regardless of whether the measurements are statistically different), and call types can be changed (eg. breeding pairs matching calls), then how can we know that there is not much mixing?
If bill size affects the food that each bird can most easily feed on, it is not surprising that birds with similar bill sizes are found feeding, and breeding, in the same areas/times of year. Birds with different bill sizes may choose to breed at other times simply because they breed when food availability is at it's best (dependent on the type of trees present).

Of course, those who support the idea that there are several 'cryptic' species that we can't readily tell apart may well be correct - they just haven't proved their case yet!
Personally I don't feel that birders have to be able to tell two birds apart for them to be valid species (as has been said, it's whether the birds themselves consider themselves sufficiently different that matters - but if the birds can 'switch', or choose different partners in different circumstances, then they are not different species).
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Old Wednesday 29th September 2010, 21:00   #44
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Which five did Grinnell recognise? (Richard)
Condor vol XIX Jan. 1917 p. 17 (available on SORA)At the time there were two subspecies vespertina vespertina and vespertina montana. Grinnell split vespertina montana into four subspecies; brooksi, californica, warreni and montana. He said that mexicana was a synonym of montana both from mountains of Northern Mexico. (I think)
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Old Wednesday 29th September 2010, 21:05   #45
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Which five did Grinnell recognise? (Richard)
Condor vol XIX Jan. 1917 p. 17 (available on SORA)At the time there were two subspecies vespertina vespertina and vespertina montana. Grinnell split vespertina montana into four subspecies; brooksi, californica, warreni and montana. He said that mexicana was a synonym of montana both from mountains of Northern Mexico. (I think)
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Old Thursday 30th September 2010, 01:42   #46
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All the quoted biometrics are statistically significant, which (to a scientist) is what defines a "real" difference. If your argument is with the overlap in morphology of a minority of individuals in a museum tray, than I guess the issue is with statistics rather than biology - and frankly I'm too tired to argue about that! I'll end by maintaining 1) that overlapping morphology is a problem with several plant species (Solidago, and other composites, especially), some flies, and probably many others. And that is without getting into Hugh Patterson's "Recognition Species" concept. In a taxa with such complex behavior as birds, I'd be amazed if they are exempt from this sort of crypsis. and 2) I still maintain that breeding behavior, not morphology, is a better basis for species, (or "Type") definition.



Very good idea. To be more challenging, I'd add redpolls to the list. However, I'd caution that one key aspect of crossbill biology and the assumed driver of population differentiation is a specialized and ephemeral food source. All of our other finches seem to be moderately general feeders (okay, compared to crossbills anyway). But they would be very good models for vocalization studies.

I don't suppose there are any good data regarding Hispaniolan vs. Two-barred Crossbill vocalizations? While those have more geographic isolation, I'd wonder if vocalizations vary in a similar way to Red Crossbills.
Hi

From looks at specimens and friends who have seen and heard Hispaniolan Crossbills, they suggest that they are in fact "red" crossbills, not White-wings. They happen to have white wingbars, but everything else about them, including biogeographic considerations suggests they are not closely related to WW, but to Reds.
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Old Thursday 30th September 2010, 12:42   #47
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I think I mentioned it on a different thread. Lack of DNA differences is a proof of gene flow between forms. Unless, miraculously, we are now witnessing a moment in evolution when crossbills first evolved call types.

Call type switching must be common. In fact, because bill sizes overlap so much, most crossbills changing call type would face no selective disadvantage, because their bills would be well within variation of the new call type.
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Old Thursday 30th September 2010, 14:50   #48
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Call type switching must be common. In fact, because bill sizes overlap so much, most crossbills changing call type would face no selective disadvantage, because their bills would be well within variation of the new call type.
I am not saying it doesn't happen but in retrap crossbills that I have processed their calls are identical to what they were up to 4 years previously. I also have recordings of colour ringed birds in the field and again these calls in situ match the ones that they gave when first caught. So it can't be commonplace.

I also think we have to be careful about using terms like "call switching". I prefer 'call syncing' as this more accurately represents the position ( I think). I am more interested in whether a shift in the calls themselves (within a population) can occur as seems to have happened with Scottish Crossbill.

As I recall ( I may be wrong) but in at least one (?) of the very few instancea of UK mixed pair breeding crossbills, the birds were identified as being different on the (different) calls they gave. As previously I can't argue with the genetic data at this point.
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Old Thursday 30th September 2010, 16:58   #49
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"Unless, miraculously, we are now witnessing a moment in evolution when crossbills first evolved call types."

Why would this be miraculous? Unless evolution stopped at some point within, let's say, the last 1-2 million years, wouldn't we expect that at least some examples of very recently diverged species would occur? That crossbills might happen to represent such a group (if indeed they do) would then be merely coincidence - not miracle.
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Old Thursday 30th September 2010, 19:29   #50
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Crossbills

Is there any study on differences in populations of Eurasian Red Crossbills? There must be any number of different call types and bill sizes, from the Atlas to SE Asia, from different mountain ranges feeding on different trees. Isnt this just one very adaptable species with different regional dialect? If call type and slight variation is the defining measure of a species, there must be hundreds of species of humans surely? You wouldnt marry someone from outer mongolia if you didnt have a clue what they were saying, so would rocky mountain crossbills breed with those from the South Hills?
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