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Scottish Crossbill (1 Viewer)

StevePreddy

Well-known member
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?
 
http://news.bbc.co.uk/1/hi/scotland/highlands_and_islands/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?
 
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
 
"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.
 
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.

Laurent -
 
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.
 
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.
 
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...

L -
 
"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
 
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
 
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.

Ian
 
Ian,

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).

Laurent -
 
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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