Crossbills (3 Viewers)

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/oc6/doneganyavendano.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_Neornithes/Grallaricula nana Bull BOC Donegan.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.

Statistics

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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).

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)

Evening Grosbeak

mb1848 said:

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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Thanks, mb.

Richard :t:

Kirk Roth said:

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.

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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.

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.

jurek said:

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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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.

"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.

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?

Russlac123 said:

You wouldnt marry someone from outer mongolia if you didnt have a clue what they were saying

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At times I wonder if that may have some merits ! :-O

Some of the common crossbills irrupting to the UK will be from East of Atlas so these have been documented; two modal bill sizes.....but a 'zillion' call types.

True, a volume control would do though!

Why dont they put a male type 1 crossbill in a cage with a type 2 female, and see if they breed and produce viable offspring? Im sure they would. Otherwise we' ll have to start splitting scousers, geordies, vegetarians, people with dentures etc based on slight DNA variations, call types and feeding adaptations, am I wrong?

breeding in captivity doesn't really count, it's whether they breed in nature. Many (most?) ducks will interbreed in captivity for instance, but we don't recognize one "duck" species.

That may be true, but the point is that their hybrid offspring would not be able to reproduce. Doesnt this define a species?

Both useful and tremendously interesting, thanks for sharing these documents!

It'll be interesting to see the treatment/discussion of Loxia in HBW15 - hopefully just days/weeks away now...
[Fringillidae is authored by Collar, Newton, Clement & Arkhipov.]

Richard

That is the definition of BSC taught in school, but not that used by scientists that adhere to that species concept. Many many animals can produce hybrid offspring that are not sterile in captivity. However in the wild such unions are rare or even nonexistant, because other factors (behavior, ecology, etc) keep them from intermingling or reproducing with other species.

If you define a "species" of bird by certain criteria, would that not apply to mammals, and therefore humans as well. A Caucasian Crossbill may have a slightly thicker bill, lower pitched call, slight DNA variation and isolated presence, and may not mix with migrant crossbills in winter. Why is this a species and an Amazonian tribesman is not? I fully support any research and I understand everything is a work in progress, but I dont understand this, please help!

What is a species?

Russlac123 said:

If you define a "species" of bird by certain criteria, would that not apply to mammals, and therefore humans as well. A Caucasian Crossbill may have a slightly thicker bill, lower pitched call, slight DNA variation and isolated presence, and may not mix with migrant crossbills in winter. Why is this a species and an Amazonian tribesman is not? I fully support any research and I understand everything is a work in progress, but I dont understand this, please help!

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Russlac,
Your starting point for trying to establish what a species (and as a corollary, subspecies) may be, has to be that there is no simple answer. I've done a fair amount of digging on this subject and have a draft article that will need much more expert advice and knowledge than I can summon, to get it into a final state!
However, one of Darwin's principal conclusions was that species, not being fixed, evolve in response to evolutionary pressures. However, there is another aspect to ‘not being fixed’ whose implications may be less obvious, and that is that the rates of evolution of contemporaneous populations of related organisms may differ, even over a short period of time. One example will serve: one of the after-effects of post-glaciation periods is that returning populations whose ‘new’ breeding areas have become geographically separated could well experience differing sets of evolutionary pressures; these might also differ from any pre-glaciation sets. Therefore, classically-driven speciation would proceed at different rates, affecting the ability of individuals from different populations to interbreed in varying ways.
Amongst birds, there are many examples of biology's tendency to be messy - in the Yellow Wagtail/Citrine Wagtail complex, the genetic isolation of some populations is variable across the breeding distribution. I think I'm right in saying that 'Black-headed Wagtail' hybridises infrequently with other 'subspecies' in the north and west of its distribution, but often, even to the extent of forming a cline, to the east and south. Here you see the difficulty in attempting any definition of subspecies that would fit, certainly covering many pages to cover every eventuality. The term 'species' has reasonably been called a 'convenient fiction'; it suits perhaps 95% of birds without any major difficulty.
If you Google the subject 'species concepts', you will probably find reasonably researched arguments that will explain why present humans genetically can be regarded as a single species. Yet in relatively recent time, Neanderthal Man, another human species died out, the evidence suggesting that for quite a period communities existed in much of Europe of both Cro-Magnon (us, essentially) and Neanderthal peoples, probably mostly amicably, despite the ferocious portrayals in 1920s and 1930s pulp fiction. Hope that helps, but it's an enormous subject that has been explored deeply in philosophical as well as scientific terms.
Beware of the world of 'woo' that may attempt to portray speciation as revealed by 'crystal pyramids' or the sudden apperance of the word 'quantum' in a Web advert!
MJB

Thanks for your view MJB, very helpful. I had already looked the subject up, it seems that there is no real definitive criteria for splitting bird species, it just depends on an individual or organisation using their own interpretations. This explains the differences between bodies, eg Clements and BOURC. From my viewpoint I can see that it is important to recognise all subspecies for conservation, but Im not sure if 30+ species of crossbills would really help anything? Where does it end, 20 odd Striated Herons, 30 Ptarmigans? I do think some splits on here are not yet warranted. These crossbills may become different species over geologic time, due to isolation and speciation but at the moment the differences are so negligable, in appearance and DNA analysis. I do think that some just like to split bird species for the sake of it, a hobby or obsessive listing tendencies!