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Old Monday 19th September 2011, 15:56   #101
crossbill7
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bombycilla wrote: "Mmmm, classification of Crossbills to "types" / species/ subspecies. How do we do this - biometrics or calls or, shock horror, behavioural data. A combination of all these ? I hate to say it but due to overlap in biometrics and morphology within the (vocal) "types" the only way is DNA analysis and even then I am not sure we "are there yet" with crossbills".

I tend to be in the "combination of all these" camp.
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Old Tuesday 20th September 2011, 01:59   #102
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What is the current thinking on the Red Crossbill population on the Dalat Plateau, Vietnam?
How about the population in the Philippines (Luzon)?
There is much talk about the vocal differences within (seemingly?) continuous American/European populations, has anyone yet looked properly at these Asian populations that are geographically very isolated?
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Old Tuesday 20th September 2011, 21:40   #103
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bombycilla,

Aren't there nearly as many Types being described across the pond? 7-9 depending on which classification system used. Have others even hinted at more splits too? I know "typing" crossbills is newer in Europe, and that certainly plays its part too....it's evolving. There's also been two different classification systems, which makes it a bit messy too. THen add that some in Spain want to split Types based on mm in morphology.
As for the looks of Groth's specs, I believe they are too clean...I'm not a fan of them based on looks....BUT, he used a good sized scale, which has not always been the case both here in States and across the pond. I see specs that are, at times, way too small IMO.
Yes, a recent German paper went a bit too far in trying to split common crossbill calls - IMO (and experience) some of the "new" calls they were claiming were merely variants of those already described. They weren't primarily researching crossbills either btw.....

European Crossbill calls can thus far be more or less described as those that go /\ (Fc2) or \/\ (Fc1) and \/\/ (Fc4) on a sonogram. I have found the type called "wandering" fc (Dutch Birding) is possibly the synonomous with "parakeet" and interestingly both "types" give an EcB. The ones on my recent post that sound like "glip" Fc4's but "look" like Fc1's are especially interesting - it sounds like one type call syncing to another type, possibly an example of "cultural" evolution (adaptation) of a crossbill call ?? !!

Agree it must be a nightmare for an American researcher with all our RSPB "types" and "glips" etc but the USA system is confusing for us too !

Splitting Crossbills on bill depth biometrics that are a fraction of a mm different (and this is the MEAN !!!) is madness - they should have used calls in conjunction which might have refined it more.

I once suggested forming a Crossbill Regulatory body - The International Crossbill Research Analysis Program ( ICRAP) to control naming of crossbill call types and perhaps they could standardize sonograms as well ! I guess all those guys still using CoolEdit will never conform to Raven ! So many "serious" researchers still use Canary and it is all very well giving your exact Filter and Fourier settings but if you don't use that program (inc. Raven !) you can't 'repeat' the settings.
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Old Tuesday 20th September 2011, 21:49   #104
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bombycilla wrote: "Mmmm, classification of Crossbills to "types" / species/ subspecies. How do we do this - biometrics or calls or, shock horror, behavioural data. A combination of all these ? I hate to say it but due to overlap in biometrics and morphology within the (vocal) "types" the only way is DNA analysis and even then I am not sure we "are there yet" with crossbills".

I tend to be in the "combination of all these" camp.
Me too, always have, but if the bios overlap and the calls switch or "adapt" then it becomes subjective hence this debate will continue. I can name (but won't) one crossbill worker who completely dismisses call analysis. He is published. Not saying he is right (I don't think he is) but just making the point. Ecological and Behavioural data is under-rated for loxia IMO.

I am really in to calls because it is something we can easily sample and "report" and given the huge overlaps in bill morphology it is something we can use to classify crossbills. But, as I said earlier, it doesn't necessarily mean we are categorizing them correctly !
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Old Wednesday 21st September 2011, 02:34   #105
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It does seem the United States types are different than Types in Europe. Other than the one Benkman bird, there's little to no evidence of call syncing from one type to another type (this was 1 bird out of 3400+ birds). Groth had birds he kept for years and he exposed them to other types in the cage and to other wild flying birds, and I haven't seen any call syncing in his collection (he didn't see any either). I haven't witnessed any synching from one call to another in my studies either, but I have witnessed what appeared to be 2 mixed pairings.....although I suspect they weren't successful and the pairings were aborted. There was no evidence they actually nested and neither pairs call matched. Sewall also forced mixed pairings and she found no convergence either (she did see slight change, but no convergence)...in fact, one Type 4 bird didn't match its Type 3 pen mate, but did call match a Type 4 across the room in a different pen. Not only that, but it seems as if only some pairs actually even go through the call syncing process. Hard to say for sure why some paired birds call match and others don't. In Groth's collection I did come across a single bird that gave a Type 1 flight call and then a Type 10 flight call in a very stereotypical repeating manner......syncing to another type seems to be very, very rare here in the States....misguided even.

The flight calls seem to be very easily typed with Type 10 being the most variable (very easy to ID by ear though), and Type 2 being somewhat variable. As for our system, it's a bit more straightforward IMO. I simply do not think the excitement calls are nearly as type-able as the flight calls....which makes sense to me. Very cool birds for sure though!! Thanks for the insight and discussion. :-)

Last edited by crossbill7 : Wednesday 21st September 2011 at 02:44.
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Old Wednesday 21st September 2011, 12:11   #106
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No I am certainly not "misguided" in appraisal of my birds (usually pairs) that are call syncing - I personally think it is quite common for crossbill pairs to call sync and this includes within a type/species. Have got a really good Scottish pair as an example somewhere. Wasn't implying that these "new" Fc1's were flying about call syncing en masse, just that they had maybe 'adapted' or evolved their call culturally in Fenno Scandia, perhaps over many years. I really do wish the stable isotope crossbill researchers had matched their geographic data to to call type data as this would have been more useful than biometrics eg. we can predict two modal sizes from existing data ! But having an idea of where these call types originate would have been most interesting.....but as I said there are some 'call deniers'.

I guess the point is, if they can/do sync their calls in the wild, especially at breeding time (when there could be an advantage in doing so), then a "real" mixed pair is not picked up by a researcher who analyses sonograms ( and finds the pairs calls are the same eg. they will be classified as the same type). That is the point I am making. The pressures and dynamics of living wild are very different to those impossed on laboratory birds, and whilst I accept their data and results for what they are, I do have my own experiences of wild birds.

The variant 1B calls I refer to on my blog are unusual in that they sound very like another type (fc4/glip) but seem to "fit" with the \/\ of Fc1 (and correspond to a B excitement call, this 1B type). No one else seems to have noticed this in UK - maybe the Dutch guys have, who have a lot of experience of Type X calls. To me a Type X Fc ( 1B or parakeet) sounds "cheep", these calls sound "ki-lip" or "gi-lip" sometimes "ki-leep" eg. more like a Fc4 ! These 'appeared' in UK last year.

The reason that they sound like Fc4 glips is that the final descending component is much higher in frequency than a standard Type X/parakeet, in my experience more symmetrical, and thus sounds similar to the high 'tail' of a Fc4/glip flight call.

At the mo in NE Scotland we have Scottish, Parrot, Common 1A (four variants of Fc), Common 4E (these invaded two years ago, some still resident) and 1B ( variant ala those I described above). Still makes only 3 species as far as I am concerned.

Would rather not discuss further in this level of detail on this site, for personal reasons, but debate can be continued openly on my blog.

Cheers,

Bomby

Last edited by bombycilla : Wednesday 21st September 2011 at 14:11. Reason: jargon correction
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Old Wednesday 21st September 2011, 12:28   #107
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As for our system, it's a bit more straightforward IMO. I simply do not think the excitement calls are nearly as type-able as the flight calls....which makes sense to me. Very cool birds for sure though!! Thanks for the insight and discussion. :-)
I think on the whole, over here, Excitement calls are still very diagnostic and useful eg. was diagnostic in determining Scottish Crossbill in some studies. Not helped that several flight call types share one Ec (B) type though. IMHO Groth slightly confused things in his descriptions and classification of Excitement Calls and Alarm calls. To me an "Alarm call" is a "shreik" or "squak" given in abject fear and panic of a predator. This doesn't seem the case with Groth (?) so he described various "states" of excitement call ?? Excitement calls are given in a mild state of threat/arousal. A (European) Blackbird, in response to a cat threat (that it knows about) gives a similar "clucking" excitement call to a Parrot Crossbill, both in cadence and pitch but gives an alarm call that is a raging cackling squabble usually as it flies in to a hedge as a Sparrowhawk threatens.

EC's are possibly harder to record - for every 30 to 40 fcs you may only get one excitement call. I stopped using a lure and only record natural response EC's even if it means following a flock for hours.

B

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Old Wednesday 21st September 2011, 14:28   #108
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Oh, no, I did not mean that you are misguided, but that is it misguided for one call type to call sync to a different call type.......and, it therefore appears very rare here in the States. The limitations of blogs. :-)
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Old Wednesday 21st September 2011, 14:29   #109
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It has been long accepted here in States that Groth should NOT have split the excitement calls and alarm calls. They are basically the opposite ends of the same continuum ....as you note.
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Old Wednesday 21st September 2011, 14:37   #110
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[quote=bombycilla;2245773]

I guess the point is, if they can/do sync their calls in the wild, especially at breeding time (when there could be an advantage in doing so), then a "real" mixed pair is not picked up by a researcher who analyses sonograms ( and finds the pairs calls are the same eg. they will be classified as the same type). That is the point I am making. The pressures and dynamics of living wild are very different to those impossed on laboratory birds, and whilst I accept their data and results for what they are, I do have my own experiences of wild birds.


Agreed on all. As you stated, it could be advantageous to call sync with another type if pressures are extreme, but as I tried stating before, overall it would seem misguided....especially if bill size and flight call cohesion within flocks matter.
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Old Wednesday 21st September 2011, 14:41   #111
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"I once suggested forming a Crossbill Regulatory body - The International Crossbill Research Analysis Program ( ICRAP) to control naming of crossbill call types and perhaps they could standardize sonograms as well "


I really like this idea of forming a Crossbill Regulatory body - The International Crossbill Research Analysis Program. Unfortunately, it probably will never happen. )-:
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Old Wednesday 21st September 2011, 14:43   #112
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I find excitement calls useful, just not nearly as useful as flight calls.

Interesting dialogue. Part of the reason why I think excitement calls are of lesser value, is, as one type gives an excitement call more in the "alarm" end of the spectrum, it can start to look (and sound) like an excitement call given at the "other" end of the spectrum by a different type. At least here in the States that seems to be the case to a degree.. I don't find that the same issue occurs when diagnosing flight calls.

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Old Wednesday 21st September 2011, 15:25   #113
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Interesting discussion. I have a couple of things to toss in:

A technical question: A while back I read that the width of the palate groove differs between call type, which makes sense since the external size of the bill would be important for opening the cone, but once the seed is out of the cone it still has a hard shell that has to be removed using the tongue and palate. A crossbill presumably has to be adapted not just to the size of the cone (e.g. larger bill for heavier cones) but also to the size of the seeds in those cones (e.g. larger palate groove for cracking larger seeds). Some heavy-coned trees have small seeds, and vice versa, so a combination of external bill measurements and palate measurements might be more diagnostic than external measurements alone. Does anyone know if this has been studied?

And for the sake of discussion: It seems logical that populations of crossbill call types would be adapting over time, merging and splitting sort of like weather systems moving across the continent. And the evidence also seems to point to the North American call types being functionally species-level populations at present. Since ALL species are constantly evolving, there seems to be a bit of time-scale bias here. We maintain Black Duck as a species, even though it is in the process of merging into Mallard. If we could come back 100,000 years in the future we would find more species blended together, but that doesn't change their current status as species. If crossbill call types are identifiable and reproductively isolated now, even if they only persist for a few hundred years they would still deserve recognition, wouldn't they?
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Old Wednesday 21st September 2011, 15:50   #114
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Hi David,

It has been studied by Benkman (1993).... He presents a palate groove structure chart (types 2-5) in his paper about the adaptation to a single key conifer (1993). As far as applying it to types and their diet, he's only applied to it Type 5 (type 5 bill depth size best fits for Lodgepole Pine, but it's palate groove structure best fits both Lodgepole Pine and Engelmann spruce -- the size of seeds in the two species are quite similar), and to a lesser extent type 3 (2010). One thing that's often left out, and Benkman has mentioned it __in passing__ several times in his papers through the years, Red Crossbill jaws are quite strong (much stronger than WW Crossbill), thus providing strength for them to be able to feed on a variety of conifers. There is a level of ecological specialization(s) with the Types, but I look at the Types as specialized generalists in a sense. For example, as Groth has told me several times, Engelmann spruce and white spruce (very, very similar species) are the universal favorite "crossbill munchies". All the types can basically handle Engelmann spruce easily.

I agree they should get species recognition if it is further proven that types are reproductively isolated. We need more studies getting at this though......which is not an easy task for a crossbill researcher. Even then, if they are proven to be reproductively isolated, there's this issue of call learning and syncing. I find this to be extremely rare (i.e. call syncing from one type to another type) and not much of a worry here in States...others could/would disagree.

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Old Wednesday 21st September 2011, 22:24   #115
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...A crossbill presumably has to be adapted not just to the size of the cone (e.g. larger bill for heavier cones) but also to the size of the seeds in those cones (e.g. larger palate groove for cracking larger seeds). Some heavy-coned trees have small seeds, and vice versa, so a combination of external bill measurements and palate measurements might be more diagnostic than external measurements alone....

....It seems logical that populations of crossbill call types would be adapting over time, merging and splitting sort of like weather systems moving across the continent.....Since ALL species are constantly evolving, there seems to be a bit of time-scale bias here........ If crossbill call types are identifiable and reproductively isolated now, even if they only persist for a few hundred years they would still deserve recognition, wouldn't they?
Hi David,

My personal view is that the whole palate groove thing is possibly most significant when the birds are breeding eg. usually feeding on open cones, when males have to feed themselves, females sitting on eggs, then chicks when they hatch eg so they can extract and husk a huge amount of seeds. Common (red) Crossbills by their very nature and for the most part are feeding on conifer cones that are not difficult to extract seeds from - here bill length may be just as important as bill depth.

Parrot Crossbills, on the other hand, have to open Scots pine cones when they are closed and the first concern is to get in to the cone ! In NE Scotland at the moment there are still some Common Crossbills feeding on closed Scots Pine as there has been another poor Larch crop and Spruce is only available 'locally'.

I have maintained that bill structure, not bill depth, is a better gauge of 'fitness' - the problem is in measuring it ! That is why we stick to minimum bill depth which though repeatable, may actually be misleading. Some Crossbills with small minimum bill depths actually have very pronounced gonyeal bulges which assist in 'cone cracking'. This is not taken in to account under current biometric measuring. It may even account for some of the overlap/range between calls and bios eg. if there was a better bill measurement then perhaps the overlap wouldn't occur. The palate groove measurement is not easy to do.

Agree with your thoughts on 'dynamic speciation'; Scottish Crossbill may well be evolving right now - due to a range of bill depths certain birds will be selected for in certain years eg. in a year of poor Larch crop, only larger billed birds at the upper range will survive/breed in preferential territory. The smaller billed birds at the lower range may be pushed in to Spruce plantations where they will encounter (and possibly breed with) Common Crossbills of similar bill morphology.

= Crossbill 'Soup' !

LC
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Old Thursday 22nd September 2011, 00:11   #116
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I agree that the more measurements the better, BUT bill depth has been chosen as THE measurement b/c it's not subjected to wear like bill length. I think wing length could be quite useful in some types/populations as well. Type 8 Newfoundland birds have a larger bill than type 2, but a shorter wing....which would make sense since one is highly nomadic (type 2) and other relatively sedentary (Type 8). This doesn't seem to apply to the relatively sedentary Type 9 South Hills birds though --they have a longer wing than Type 2. Palate groove structure is very hard to measure...and again, it really hasn't been applied to any of the types except for Type 5. Behavior, movements, etc are very underrated when it comes to studying crossbills. Stay tuned.

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Old Thursday 22nd September 2011, 10:09   #117
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Any links to more info martinf?
You could start with this
http://homepage.psy.utexas.edu/Homep...&%20Kruger.pdf
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Old Thursday 22nd September 2011, 11:31   #118
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I agree that the more measurements the better, BUT bill depth has been chosen as THE measurement b/c it's not subjected to wear like bill length. I think wing length could be quite useful in some types/populations as well.
No, I am not a fan of a lot of bill measurements I only measure bill depth (minimum), bill width and bill length. Tried to do maximum bill depth (from the feathering on the crown to the lowest point of gonys) but it was too variable, certainly on live specimens. I want to process and release birds as quickly as possible. Bill length is the least reliable measurement sometimes even within an observer never mind between !

Wing is ok as a guide/corroborating evidence but some crossbill 'populations' and 'types' again seem to have the usual overlap.

L
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Old Thursday 22nd September 2011, 14:27   #119
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Thanks.
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Old Thursday 22nd September 2011, 16:19   #120
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How about the population in the Philippines (Luzon)?
There is much talk about the vocal differences within (seemingly?) continuous American/European populations, has anyone yet looked properly at these Asian populations that are geographically very isolated?
I guess from the lack of response so far there's not much research on the Asian populations - I can't comment on the merit of the various arguments for specification in Europe and the US but if any of those are valid it's hard to believe all the Asian populations wouldn't be distinct species.
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Old Thursday 22nd September 2011, 18:50   #121
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Sorry viator, I'm not that familiar with Asian Crossbills. I do know of a recording of an Asian Crossbill in the Borror Lab of Bioacoustics that showed quite the resemblance to Type 1 in North America. There appears to be a finite number of different flight calls that Red/Common Crossbills give, and therefore you find similarities between flight calls from continent to continent. I'm not saying they are exact matches, but they can be quite similar.

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Old Friday 13th January 2012, 08:01   #122
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Spain

Edelaar, Alonso, Lagerveld, Senars & Björkland (in press). Population differentiation and restricted gene flow in Spanish crossbills: not isolation-by-distance but isolation-by-ecology. J Evol Biol. [abstract]
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Old Tuesday 17th January 2012, 11:52   #123
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I’ve read through this thread with great interest. My understanding of the arguments are:

It is proposed that the use of different types of conifers for foraging can result in the formation of subspecies/species of crossbills by limiting opportunities for gene flow. The idea is that birds with different sized beaks are better adapted at extracting seeds from some types of cones than others – big beaks for tough pine cones, slender beaks for little larch cones etc. By foraging in flocks Crossbills can feed more efficiently. This efficiency for an individual is increased if the other members of your flock have similar sized beaks and feed on the trees that best suit your beak size. Breeding success is increased if your mate has a similar beak size. Birds with different sized beaks tend to have different types of calls. The distinct calls allow Crossbills to form flocks and pairs with birds that have a similar sized beak and conifer preference. Consequently gene flow between birds with different sized beaks is limited. Additional factors such as coning patterns of tree species also influences the opportunity for forming mixed flocks/pairs – eg cyclic coning patterns of spruces (promoting nomadic behaviour) v. regular coning of pines (promoting sedentary behaviour). So, there is evidence that differences in feeding ecology could lead to adaptations that result in breeding isolation from other Crossbills living in the same region that have a different feeding ecology. At the extreme ends of the beak-size range the extent of interbreeding (gene flow) is so limited that they are regarded as full species (Parrot v Common Crossbill). In the middle of beak size range is the ‘Scottish Crossbill’.

To me, identifying Crossbill species by call and beak size seems to be fraught with problems. I’m not so sure how easy it is to categorize Crossbills in terms of beak size or call type. Variation in Crossbill calls may simply be a physical consequence of beak size and syrinx size (this has been shown in Darwin’s Finches). If so, call types may also show continuous variation (like beak size) and they may not be easily categorised as one type or another. How distinctive are these named Crossbill call types? Are some calls intermediate types? Furthermore, calls may be learned to a greater or lesser extent (and the ability to match call types could be constrained by beak/syrinx size). Nor do we know how constant specific call types are over time – do they ‘evolve’ at a rapid rate – changing within the lifetime of a bird, over years, decades?

The Scottish Crossbill is classified as a full species on the basis that it supposedly has a diagnostic call i.e., there is a call only given by birds with a beak size that is intermediate (but overlapping) on the scale from small (Common) to large (Parrot). Birds with this diagnostic call apparently do not breed with larger and smaller beaked birds that do not possess this call (though the evidence for this claim seems fairly weak). It is certainly interesting that no such intermediate-sized Crossbills occur in Scandinavia where Parrots and Commons co-exist. Or is this because nobody has looked yet?

Subspecies are the result of geographic separation (which could also involve ecological separation). In animals geographical separation is implicit in the definition of a subspecies. So differentiation based solely on ecology, as in the case of Crossbills, creates a taxonomic problem. This is compounded when the degree of separation is not so clear (as in the case of Scottish Crossbill). So whatever you decide to call them – species, subspecies, call-types – it seems to me the problem for birdwatchers/taxonomists is that it is difficult (impossible?) to categorize the continuous variation that is exhibited by Crossbills in terms beak size, call variations and degree of gene flow. Evolutionary biologists don't really need to categorize the different Crossbill types - they just need to demonstrate the process of adaptation/isolation. Personally, I think I’ll stick with Parrot, Common and Two-barred as being ‘species’ in the Palearctic – with the rest being intermediate, locally adapted subspecies of the Common Crossbill.
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Old Saturday 21st January 2012, 21:16   #124
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In the middle of beak size range is the ‘Scottish Crossbill’.
Not so. mean Scottish Crossbill bill depths are closer to Common Crossbill


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To me, identifying Crossbill species by call and beak size seems to be fraught with problems. I’m not so sure how easy it is to categorize Crossbills in terms of beak size or call type.
Not if they are taken together and combined with ecological behavioural parameters. As I have said on here before, moult is also a useful indicator of species as is the temporal presence of streaked juveniles (with adult birds that are feeding them).

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Variation in Crossbill calls may simply be a physical consequence of beak size and syrinx size (this has been shown in Darwin’s Finch.If so, call types may also show continuous variation (like beak size) and they may not be easily categorised as one type or another. How distinctive are these named Crossbill call types? Are some calls intermediate types?
Plenty of papers available on the categorization of calls. Some are distinct, some are variable but with experience (in the field) they can mostly be described and assigned to type, especially by correlating flight calls with alarm call. Darwins finches as a group have huge variability in bill structures whereas Crossbills don't (relatively), so not sure I buy your argument.


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Nor do we know how constant specific call types are over time – do they ‘evolve’ at a rapid rate – changing within the lifetime of a bird, over years, decades?
Some calls have remained stable in Deeside over 30 plus years, others appear to have "shifted". I am going through recordings of Alan Knox from the 70's to early 90's and the calls for most types are the same (so far). Have sound recorded colour ringed Pine crossbills in the field, or retrapped, and the calls were all the same. On the flip side I have released Common Crossbills that give 3 versions of a call.

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Originally Posted by Andrew Dixon View Post

It is certainly interesting that no such intermediate-sized Crossbills occur in Scandinavia where Parrots and Commons co-exist. Or is this because nobody has looked yet?
There is no overlap in museum crossbill specimens from Scandanavia. Scotland is a small country with a large mosiac of conifer species in relatively close proximity.

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Originally Posted by Andrew Dixon View Post
it seems to me the problem for birdwatchers/taxonomists is that it is difficult (impossible?) to categorize the continuous variation that is exhibited by Crossbills in terms beak size, call variations and degree of gene flow.
I disagree. It is actually easy to categorize these things, it is just that we may not have categorized it correctly ( cf the 'real' Scottish Crossbill ) ! Whilst Scottish Crossbills that I have recorded (and caught and measured) appear to have a different call from those previously described by others (?), they are all 'Scottish Crossbills' on bios, breeding behaviour, ecological factors. In other words we are still describing birds consistent with 'Scottish Crossbill'.

The relict Caledonian Pine Crossbill, IMO, would be consistent with what we call Parrot Crossbill here in Scotland today - it is the only type that can survive on closed Scots Pine Cones in mid winter and at one point in the not too distant past that was all that was available. Scottish Crossbills (today) prefer Larch in Autumn, Winter and early Spring. The planting of millions of Larches in Scotland in the 18th Century possibly selected for smaller billed native birds which could then breed on them. Common Crossbills irrupting to Scotland would also be able to breed in Autumn and Winter as well as Summer on Scots Pine. Thus the Scottish Crossbill 'soup' may have started.

More stuff and pics of the Scottish types here http://pinemuncher.blogspot.com

LC
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Old Thursday 1st March 2012, 07:18   #125
Richard Klim
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Two-barred/White-winged Crossbill

Benkman 2012. White-winged Crossbill (Loxia leucoptera). BNA Online 027 (revised 17 Feb 2012).
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Relationships within Loxia are muddy chiefly because species limits within the L. curvirostra complex are controversial. That aside, it is clear that there are two species complexes in the genus: the L. curvirostra complex, which contains between one and ten (or more) species, and the L. leucoptera complex, which contains between one and three species, in the latter case with species limits corresponding to named subspecies. Loxia megaplaga Riley, 1916, the Hispaniolan Crossbill, was considered a subspecies of L. leucoptera for many decades, but on the basis of vocal, morphological, and genetic divergence (Benkman 1994, Smith 1997, Parchman et al. 2006, 2007), the taxon generally is treated as a species now (e.g., Banks et al. 2003). Loxia megaplaga diverged from L. leucoptera roughly 550,000 years ago (Parchman et al. 2007). Given marked differences in voice (Elmberg 1993), coupled with morphological (and posited ecological) differences, Old World and New World L. leucoptera also may be species rather than subspecies.

Hybrids between species groups are unknown in the wild. A male L. leucoptera caged with a female L. curvirostra produced two broods of three young each (H. B. Tordoff pers. comm.). A resultant male hybrid, which had wing bars and bill size intermediate to its parents, was backcrossed with a female L. curvirostra. The offspring "appeared essentially like" L. curvirostra (H. B. Tordoff pers. comm.).
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