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Scottish Crossbill (1 Viewer)

There are some Common Crossbills with very distinctive calls (no sonograms needed)... and there are a few which are agonisingly close to Parrot (and if they get too close for Magnus Robb I give up).

An excellent (and careful) contribution from Laurent.
 
Tally Ho !

I hope everyone's got their tin hats and flak jackets for when Lindsay returns to this thread ;)


Moi' ? Surely not :smoke:

Actually, some interesting 'theories' floating about but again the usual 'desk project' type stuff eg. theoretical in bias rather than based on field experience and observation.

About to go "over the top"...........
 
Listen To This

OK. difference is just perceptible by ear

Not true. If you can't tell the difference between a Parrot Ec and a Scottish Ec then you should possibly listen a bit more closely ! A Parrot EcD and a Common EcA is harder granted. With a little practice it is possible to separate Fc1's from Fc4's - other people on here are saying they can do it.

Do the differences is sound matter to us anyway, surely it is what the bird perceives as the signifier that is more important ?
 
Linz,

Actually, some interesting 'theories' floating about but again the usual 'desk project' type stuff eg. theoretical in bias rather than based on field experience and observation.

Message received.
(I certainly have no (well, very little) field experience with crossbills in Scotland.)
I would argue, though, that anyone equating the Scotland crossbill case down to a taxonomy problem (a do-we-have-one-or-two-or-three-"species" question), is quite unavoidably taking a theory-biased look at them...

L -
 
Lack of DNA differences mean free DNA flow between three bar-less crossbills (common, scottish and parrot) and they are one species.

Did you really just say that ? Believe me they are NOT acting as 'one species' ! They have completely different morphology that allow for ecological specialisation on different food sources - think Darwin's finches on the same islands never mind across the whole of the Western Palearctic !

"Difference" in calls and "assortative mating" observed can be easily explained:

- differences in both bill size and calls are minute and prone to error (we talk about milimeter-two differences measured by hand on living bird. And call differences imperceptible by ear and judged by eye on sonograms).

Difference in bill size between Common, Scottish and Parror Crossbills is anything but minute. Between the curvirostra 'complex' maybe. Regarding error in measuring Marquiss and Rae solved this by only one ringer doing all the measurements in a 10 year study " The mean difference between consecutive measurements for 23 full-grown birds was 0.10mm ie. 0.9% of mean bill depths". That is not "prone to error". I would also add that having caught and handled all three species (!) they are different not just in bill morphology but also wing length and body size - these birds are not the same species. Regarding sonograms I have gone into this on other threads - I use my ears as well and don't just "judge by eye", that would be lazy.

- sample size was small (my apologies to field researchers, I know that crossbills are very difficult to follow),

The Dutch apparently have a paper coming out with a sample of over 500 curvirostra, biometrics and calls ( I think it is available to preview ? ). Marquiss and Rae caught 437 Crossbill in Deeside. Small sample size - maybe, given there three (4?) types, but still valid don't you think ?

- "assortative mating" is well known within species (lots of ecological races like tree-breeding and cliff-breeding peregrines, even city pigeons tend to pair with lookalikes to some extent).

Well if they are all one species as you say, in my patch there sure as heck is a helluva lot of really big billed ones that tend to stay on one pinewood territory and breed in the same area with birds that give the same calls and have the same bill morphology. Oh, and their progeny look and sound the same. This is all as a result of an ecological factor.

- there is no indication that observed mating pattern is constant (what happens e.g. in years of poor seed crop or during long waderings)?

Common Crossbills tend to form flocks with birds that give the same call. There may be two main call types present in a large group of birds, but they are in groups with individuals that share the same characteristics (pers. obs). I can validate this by having spent time catching them at drinking sites. You catch 10 birds and they tend to be one type. An hour later you catch another 8, a different type. The same BTW happens with Scottish and Parrots. They are like women - they all go for a piss together, or in the crossbills case a drink ! They are acting as groups suggesting they have bonds within those groups.

- if they were species, we should observe pattern NOT strictly following bill size: large-billed and small-billed individuals of one species would prefer each other against other species apporaching it them in bill size.

Bill size seems to be important, though an optimal bill is not necessarily the biggest one. Your argument only holds any water IMO where there is a 'clinal ' or intermediate form such as Scottish Crossbill, which is somewhere between Common and Parrot in morphology, the latter two isolated by niche preference. Also, a small billed Parrot at say 11.9mm is a very different looking bird from a big Common at 11.5mm so can't see them pairing.

- calls were not studied to be inherited and constant. In fact, many finches are known call learners.

Calls can be learned, no one is denying that. But juvenile crossbills learn the calls of their parents who mostly happen to share a distinct 'call type'. I have seen call convergence several times in crossbill pairs and never has it IMO been a Parrot trying to sound Scottish or vice versa. Rather, it is a pair bonding and trying to sychronize their own particular calls within the parameters of their own 'type'.

Not meaning to single you out, it's just you had said a lot of stuff I felt was , in my opinion and experience, misinformed. ;)


Lindsay
 
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I would argue, though, that anyone equating the Scotland crossbill case down to a taxonomy problem (a do-we-have-one-or-two-or-three-"species" question), is quite unavoidably taking a theory-biased look at them...

L -


............possibly, but hopefully a 'theory' resulting from an interpretation of ones data and experience with the subject. ;)

The problem with Scotbill is paradoxical in that people who have never seen one, and probably never will, are telling people who have studied them for years that "they don't exist" or are not acting as species !

Personally, I think a lot of the points you made were well put and were thought provoking.

IMHO Scotbill is a 'casualty' of the self-fullfilling prophecy........


Lindsay
 
They found no significant difference whatsoever in microsatellite data.
They found a very slight overall variation in mitochondrial control region sequence data (up to 0.15% - this is certainly not more than what you should expect in a single population - note that the CR is a gene that is used to compare very closely-related taxa, because it evolves particularly fast), and this variation was completely unrelated to morphology - i.e., birds from every morphological types were spanned all over the whole tree.
I agree with Jurek on this, this is no differenciation at all.

The paper is here : http://dx.doi.org/10.1098/rspb.2001.1015

The only really consistent genetic divergence to have been detected up to now in plain-winged crossbill, is between American and Eurasian populations (as a whole, i.e., Eurasian populations including parrot and Scottish).

Laurent -

Hi Laurent,

I am not sure this changes anything. We can go as deeply into this as anyone chooses but the fact remains, these birds are different. The original released report was represented in BBC Wildlife some years ago and just about everyone agreed that there was a lot more to speciation than we had previously thought. As I said elsewhere, these techniques are relatively new and it is a confident prediction that there will be more examples of this kind as (or if) the research is extended. I suppose the final decision comes down to whether you (individual choice) think these birds are worth preserving.

I stand by what I said, that we can apply evolutionary theory to only a snapshot of what is in front of us. In that sense, there is no reason to dismiss the idea of speciation at every possible stage - we just need to know where to look (and possibly, re-assess our ideas about what a species is anyway).

Ian
 
OK. difference is just perceptible by ear. But it is tiny comparing to other species groups identifying each other by call (e.g. song of chiffchaff and willlow warbler).

I also never seen clear discussion of these call types - how variable they are, how intermediates and types are sorted.*

Hi Jurek,

I should make one thing clear before we carry on, I am not keen on splitting. ;)

Lindsay does a much better version of this than I can do but we should not forget that there are a number of things that define a species. For example, should chiffchaff and willow warbler (unlikely) be preserved as fossils, it is very likely that they would be classed as the same species. Indeed, it is likely that virtually every dinosaur discovered apart from the occasional communal burial, is a separate species under the rules we currently apply. I realise this is a personal opinion but my understanding of evolution tells me that we should not have the present static state that traditional classification has given us. Therefore, it is no surprise to me that the more we dig, the more we find intermediate situations. The crossbill situation suggests Gould's Punctuated Equilibrium theory of evlution but we do not know what produced this situation and as I pointed out previously, the races (is this a safe term?) could have evolved separately but have been thrown back together through processes that we do not understand. Alternatively, we could have a species survival strategy equivalent to bet-spreading (see Lindsay's appraisal of feeding strategies) that suggests a mechanism for speciation even if it is not direct evidence that it has taken place.

* I have seen sonograms and there is no question that the structure is different. Bird song is (mostly) faster than the human ear can detect so that any audible difference is likely to be very significant. Translate this to an electronic trace (sonogram) and the instrumentation picks up much more than our ears can detect. I worked on elephant communication (sadly, only captives) for a brief time and part of the evaluation work involved me testing sonograms to asses the instruments before use.

Ian
 
I suppose the final decision comes down to whether you (individual choice) think these birds are worth preserving.

Hi Ian,

Two things that I would like to be convinced of:

- That a crossbill morphotype that evolved in a Scotland in which the only conifers available for foraging were Caledonian pines, is something preservable in the present (very different) situation. I'm really not convinced it is, unless you cut down all these artificial, alien tree plantations, which is obviously unfeasable.

- That Scottish parrot crossbills are really more parrot than Scottish. This comes from a theoretical reasoning again, agreed... But anyway: one consequence I could foresee, of having smaller-cone tree plantations added in the vicinity of the Caledonian forest, would be a selective emigration of smaller-billed crossbills from the forest to these plantations. The logical consequence would be an increase of bill size in the Caledonian forest population, and the apparition of an intermediate-billed population in the plantations... Which as far as I can see is exactly what happened.
Who knows what was the actual call of the type of Loxia scotica?

Laurent -
 
Hi Jurek,

I should make one thing clear before we carry on, I am not keen on splitting. ;)

The crossbill situation suggests Gould's Punctuated Equilibrium theory of evlution but we do not know what produced this situation and as I pointed out previously, the races (is this a safe term?) could have evolved separately but have been thrown back together through processes that we do not understand. Alternatively, we could have a species survival strategy equivalent to bet-spreading (see Lindsay's appraisal of feeding strategies) that suggests a mechanism for speciation even if it is not direct evidence that it has taken place.


Ian


Ian,
I'm a little out of touch with my Gould (haven't read any of his stuff for a while, and haven't read any of the later books he wrote). Would you mind explaining what Punctuated Equilibrium Theory is please?

Or failing that, direct me to the Gould book that explains it?

Thanks very much!

Am finding this a fascinating thread BTW. Commenting from a position of relative ignorance, it does seem as though crossbills are a perfect opportunity to study various aspects of the evolutionary process. It's true what somebody has already mentioned - we do seem to be very fortunate in the timing of our available "snapshot" of study (at least in the opportunity for gathering information; the differing interpretations of that data is possibly another matter!).
 
It's true what somebody has already mentioned - we do seem to be very fortunate in the timing of our available "snapshot" of study

...Maybe. Or we are not particularly fortunate, and what we are seeing here happens to crossbills (and Darwin's finches, sticklebacks, etc.) all the time... (Or at least every time they have to face a new or modified environment.)
Which wouldn't make it less interesting, by the way.
 
...Maybe. Or we are not particularly fortunate, and what we are seeing here happens to crossbills (and Darwin's finches, sticklebacks, etc.) all the time... (Or at least every time they have to face a new or modified environment.)
Which wouldn't make it less interesting, by the way.

Well, I suppose technically, a particular species is constantly having to face a new or modified environment, which in turn affects its evolutionary process. If I remember correctly, then evolution was traditionally regarded as proceeding at a relatively constant, slow process, but our old friend Gould hypothesised that in fact this slow pace was occasionally interrupted by bouts of vastly increased evolutionary pace (I know that's not the best way of stating it!). However, even these "speeded up" phases still happened at a pace that was too slow for our perceptions.

I suppose we just have to make the best of our particular window of opportunity, and collect as much data as we can, and formulate theories accordingly. But you're right, it doesn't make it any less interesting.
 
Believe me they are NOT acting as 'one species' !

Hi,

I think you have wrong impression that "species" is a pool of identical individuals.

Lots of species have ecological races, local variants, differently behaving groups which are not even subspecies. Differences between plain-winged crossbills (better name than bar-less!) are on this level.

I don't follow literature much, but closest example I know are killer whale pods. Transient and resident whales occur in about the same areas, but have different food (sea mammals vs fish), different calls and subtly different apperance (fin shape). Killer whales were isolated for several thousand years on DNA, so the genetic difference is larger than crossbills, but are nothing more than ecological races. I'm sure somebody can find example of ecological race even more similar to crossbill case.

They are, of course, always fascinating to study.
 
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I'm sure somebody can find example of ecological race even more similar to crossbill case.

Geospiza Darwin's finches are a classical example that presents similarities with the crossbill case, as also noted in the recent Summers et al. paper posted here yesterday. They are classically treated as species under the BSC, which is presented by Summers et al. as an argument for treating the three Scottish Loxia types as distinct species. But there are other points of view... Bob Zink's discussion, published in Auk in 2002, is particularly interesting on this subject:
http://www.cbs.umn.edu/eeb/faculty/ZinkRobert/ANewPerspective.pdf

These are amazing cases, in which loose applications of the BSC can typically lead to more splitting than careful applications of the PSC - quite the opposite of the usual situation...

Laurent -
 
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Hi Jurek,

A Parrot Crossbill, with a bill of 13.0+ mm, wing 108mm specialising on Scots Pine cones and a Common Crossbill with a bill of 10.0mm, wing 96mm specialising on Norway Spruce are the same 'species' ? Come on ! They may share a common ancestry but are you really telling me that there can be that much diversity and variation within what you call a single 'species' ? I am not comfortable with them being classed only as 'sub-species' either, but maybe that is just me ?

Lindsay
 
- That Scottish parrot crossbills are really more parrot than Scottish. This comes from a theoretical reasoning again, agreed... But anyway: one consequence I could foresee, of having smaller-cone tree plantations added in the vicinity of the Caledonian forest, would be a selective emigration of smaller-billed crossbills from the forest to these plantations. The logical consequence would be an increase of bill size in the Caledonian forest population, and the apparition of an intermediate-billed population in the plantations... Which as far as I can see is exactly what happened.
Who knows what was the actual call of the type of Loxia scotica?

Laurent -

You need to read the paper that I have finished writing ! Will hopefully be in print this year, or early 2009 at latest.

I also have my own 'theories' as to the origins of Scotbill but these are just hypothetical, though I am examining what evidence I can. This (different) paper is much more controversial !!!!

Lindsay

Lindsay
 
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