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Old Tuesday 15th January 2008, 22:00   #1
StevePreddy
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Scottish Crossbill

Nice to see Scottish Crossbill featured on the front of the Times newspaper today. In their article they state "Two years ago the bird won recognition as a distinct species after analysis of its beak and its “Scottish accent”. Can anyone shed any light on the "two years ago" bit of that sentence? My understanding was that Voous & BOURC adopted the split in the 1970s, and despite rumours & counter-rumours about the taxonomic status of ''scotica'' since then, it's always been regarded as a full species. Was there a 2006-ish study/ies into morphology & voice which has passed me by?
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Old Tuesday 15th January 2008, 22:22   #2
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http://news.bbc.co.uk/1/hi/scotland/...ds/4793863.stm

"The British Ornithologists Union has classed the Scottish crossbill as a separate and distinct species since 1980.

However, the RSPB admitted to having been sceptical in the past and had cited a lack of scientific evidence to back up its endemic status."
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Old Tuesday 15th January 2008, 22:33   #3
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http://news.bbc.co.uk/1/hi/scotland/...ds/4793863.stm

"The British Ornithologists Union has classed the Scottish crossbill as a separate and distinct species since 1980.

However, the RSPB admitted to having been sceptical in the past and had cited a lack of scientific evidence to back up its endemic status."
Thanks for that, Menzie. Presumably that's the work the Times is referring to. Any idea who it was done by and where/when it was published?
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Old Tuesday 15th January 2008, 23:38   #4
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Thanks for that, Menzie. Presumably that's the work the Times is referring to. Any idea who it was done by and where/when it was published?
"Assortative mating and patterns of inheritance indicate that the three crossbill taxa in Scotland are species", Ron W. Summers, Robert J.G Dawson and Ron E. Phillips ( J.Avian Biol. 38:153-162, 2007).

In order to do a survey to estimate the numbers of scotica it had to be 'proved' that they were a species - you can't survey a species that doesn't exist ! Or can you ?

Lindsay
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Old Wednesday 16th January 2008, 01:18   #5
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Originally Posted by griffin View Post
"Assortative mating and patterns of inheritance indicate that the three crossbill taxa in Scotland are species", Ron W. Summers, Robert J.G Dawson and Ron E. Phillips ( J.Avian Biol. 38:153-162, 2007).

In order to do a survey to estimate the numbers of scotica it had to be 'proved' that they were a species - you can't survey a species that doesn't exist ! Or can you ?

Lindsay
Any search using 'Piertney' (combined with 'crossbill') will also reveal the background to this story. I am no geneticist but the electrophoresis results showed less degree of difference between that expected between subspecies over the three previously designated species. However, there was so much more to consider between the song profile, geographical overlap and the fact that the three races/species do not interbreed, that more research was essential.

My personal feeling is that any research in this area (crossbills) is fundamental to our understanding of how evolution works. The questions that occur to me are:

Can interbreeding with viable young produced (see any number of Aythya or Anas crosses) between dissimilar species be the mechanism to fuel Punctuated Equilibrium (formulated by Stephen Jay Gould)?

Or, is there a throwing together of species (previously separated geographically [example: house sparrow - tree sparrow] showing that there is a slower parallel development away from the ancestral form (Darwinian evolution)?

Or, is there some middle ground?

Ian

P.S. We should definitely protect those species that we have or suspect and (wherever possible) prevent artificial inter-mixing.
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Old Wednesday 16th January 2008, 07:07   #6
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Regional variation is all it is. Nice one 'Times'.
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Old Wednesday 16th January 2008, 10:48   #7
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Regional variation is all it is. Nice one 'Times'.
Not exactly. Ecological, not regional variation.
A type of variation that is not normally assumed to happen within a species by the taxonomic model - which is what makes their treatment difficult.

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Old Wednesday 16th January 2008, 11:39   #8
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Regional variation is all it is. Nice one 'Times'.
Except that it isn't regional variation, because all the different types/species (whatever you want to call them) of crossbill (including at least three types of Common crossbill) can be found in the same place apparently choosing to pair with mates that give the same call.
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Old Wednesday 16th January 2008, 12:22   #9
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Lack of DNA differences mean free DNA flow between three bar-less crossbills (common, scottish and parrot) and they are one species. OK, one might argue that, by amazing timing, we captured sudden differentaition of Loxia in the making, but it is unlikely.

"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).
- sample size was small (my apologies to field researchers, I know that crossbills are very difficult to follow),
- "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).
- there is no indication that observed mating pattern is constant (what happens e.g. in years of poor seed crop or during long waderings)?
- 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.
- calls were not studied to be inherited and constant. In fact, many finches are known call learners.

That it is possibly bad news to conservation of wonderful nature in Scotland is another matter.
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Old Wednesday 16th January 2008, 12:40   #10
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And call differences imperceptible by ear and judged by eye on sonograms).
Really? Even I can now detect the differences between some of the calls by ear (although sonograms are a useful confirmation).
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Old Wednesday 16th January 2008, 12:59   #11
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Except that it isn't regional variation, because all the different types/species (whatever you want to call them) of crossbill (including at least three types of Common crossbill) can be found in the same place apparently choosing to pair with mates that give the same call.
Crossbills are a highly specialised group using a quite peculiar foraging strategy, with a lot of unexpected (but more or less direct) consequences.
They feed on a resource that can't be assessed by sight - they have to land on a tree and try the cones to see if they are suitable for them. A single bird will have to try many cones to decide whether a tree is interesting or not; in a flock of birds, the decision is taken much faster because the group integrates the behavior of its component birds, so that each bird has to test fewer cones. This increases the efficiency of foraging, and is thought to be one of the main reasons why crossbills feed in flocks each time it's possible (even while breeding).
Even minute changes in a crossbill's bill structure affect the type of cones that it can feed on efficiently. For their foraging method to work, a given tree should obviously be interesting (or not) in the same way for all the birds in the group, otherwise integrating the assessment over the group would be a very poor strategy; as a consequence, feeding groups must always be homogeneous in terms of bill structure.
Using calls as a rallying signal prevents the merging of a group with other groups having (potentially) different bill structures. Some characteristics of these calls (frequency?) might be constrained by bill size/structure more or less directly (thus be a real signal reflecting bill structure itself), but otherwise the calls are apparently learned (as is the case in most carduelids; in fostering experiments by Jeff Groth in North America, fostered crossbill chicks ended up giving the calls of their foster parents, not those of their biological parents).

Crossbills mate mostly within their feeding group, so there is absolutely nothing surprising in the fact that they mate assortatively in terms of call and bill structure. The opposite would in fact have been most surprising.

Several forms that coexist at a single location cannot be subspecies, because in taxonomy subspecies always refer to geographical variation. Local morphological variation associated to ecological specialisation could mean either that you have species, or that you have ecologically specialised morphotypes, the latter having no standing in the taxonomic model. I believe that whether you have one or the other should depend on the long term isolation and stability of the forms. The fact that the mitochondrial phylogeny is a complete mess is indeed not really a good signal that this has been the case in the past...

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Old Wednesday 16th January 2008, 14:05   #12
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Originally Posted by griffin View Post
"Assortative mating and patterns of inheritance indicate that the three crossbill taxa in Scotland are species", Ron W. Summers, Robert J.G Dawson and Ron E. Phillips ( J.Avian Biol. 38:153-162, 2007).

In order to do a survey to estimate the numbers of scotica it had to be 'proved' that they were a species - you can't survey a species that doesn't exist ! Or can you ?

Lindsay
Do you know if the paper is online anywhere, or how I could get hold of it (without subscribing to J.A.B)?

Cheers,

John
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Old Wednesday 16th January 2008, 15:14   #13
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Do you know if the paper is online anywhere, or how I could get hold of it (without subscribing to J.A.B)?

Cheers,

John
see attached.......
Attached Files
File Type: pdf Summers et al 2007.pdf (189.1 KB, 300 views)
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Old Wednesday 16th January 2008, 15:15   #14
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Originally Posted by jurek View Post
Lack of DNA differences mean free DNA flow between three bar-less crossbills (common, scottish and parrot) and they are one species. OK, one might argue that, by amazing timing, we captured sudden differentaition of Loxia in the making, but it is unlikely.

That it is possibly bad news to conservation of wonderful nature in Scotland is another matter.
Hi Jurek,

Just a slight correction here - The study did not find a lack of difference just less difference than we would normally expect between known and accepted subspecies. Having said that, the degree of difference suggests unbarred crossbills could be regarded as a superspecies and potentially (sorry guys), lumped.

I genuinely think this is a case of Loxia speciation and it is what we would have expected to see from a prediction of evolutionary theory. The difficulty was, we never knew what to look for or where to look before. Electrophoresis and mitochondrial DNA examination are relatively new techniques and there revealing an enormous amount of information. The main problem was evolutionary theory is that we are working with a snapshot in time and we have no way of knowing what the future would bring although we can have a go:

Scenario 1: All three crossbills continue to diverge, producing three genetically distinct species.

Scenario 2: For some reason, the three crossbills (or any two) begin to hybridise/cross-breed meaning that at least one variety/species disappears.

Scenario 3: One or more of the varieties/species becomes extinct (relevant to the RSPB press release) for environmental reasons. Should this be the intermediate Scottish crossbill, the genetic difference between parrot crossbill and common crossbill would be within what is expected for subspecies.

Ian
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Old Wednesday 16th January 2008, 15:21   #15
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Really? Even I can now detect the differences between some of the calls by ear (although sonograms are a useful confirmation).
Indeed, I think the calls and songs had been audibly described as being different but sonograms proved they were structurally different too. In some ways, the DNA results were unexpected when viewed against other aspects of crossbill ecology.

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Old Wednesday 16th January 2008, 16:03   #16
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Ian,

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Just a slight correction here - The study did not find a lack of difference just less difference than we would normally expect between known and accepted subspecies.
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).

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Old Wednesday 16th January 2008, 16:14   #17
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I hope everyone's got their tin hats and flak jackets for when Lindsay returns to this thread
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Old Wednesday 16th January 2008, 16:40   #18
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Crossbills are a highly specialised group...(and more about crossbill peculiarities)
Hi, can you direct me to any paper about that?
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Old Wednesday 16th January 2008, 16:46   #19
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Indeed, I think the calls and songs had been audibly described as being different
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.
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Old Wednesday 16th January 2008, 18:00   #20
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Hi, can you direct me to any paper about that?
Craig Benkman's publications :
http://www.uwyo.edu/benkman/
...are a pretty good start.
(But there are many ;-))

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Old Wednesday 16th January 2008, 20:02   #21
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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.
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Old Wednesday 16th January 2008, 20:30   #22
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Tally Ho !

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

Moi' ? Surely not

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"...........
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Old Wednesday 16th January 2008, 20:34   #23
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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 ?
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Old Wednesday 16th January 2008, 21:28   #24
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Linz,

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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...

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Old Wednesday 16th January 2008, 21:30   #25
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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 !

Quote:
"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.

Quote:
- 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 ?

Quote:
- "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.

Quote:
- 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.

Quote:
- 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.

Quote:
- 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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