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The Barcode of Life project uses a segment of mitochondrial DNA as a 
measure of genetice differences between species.  Mitochondrial DNA is 
inherited from an individual's female parent, so it's matrilineal, and 
doesn't change from generation to generation.  However, mtDNA does 
change over time due to random mutations.  On average, most bird species 
are believed to show a 2% change in their mtDNA every million years.  So 
the genetic divergence between two species that split 2 million years 
ago would be 4%.  By comparing strands of mtDNA the researchers feel 
they have a good handle on genetic diffrences, and therefore species 
differences.  The fact that some species are genetically similar (Ross' 
vs. Snow Goose, Yellow-billed vs. Black-billed Magpie), doesn't mean 
they're not separate species, it just means they haven't been separated 
long enough for this technique to show great differences ( i.e., mtDNA 
analysis is a very blunt instrument). 

If you check the list of species considered different (Northern Fulmar, 
Solitary Sandpiper, Western Screech Owl, Warbling Vireo, Mexican Jay, 
Western Scrub-Jay, Common Raven, Mountain Chickadee, Bushtit, Winter 
Wren, Marsh Wren, Bewick's Wren, Hermit Thrush, Curve Billed Thrasher 
and Eastern Meadowlark), and then look in A.C. Bent's "Life Histories of 
North American Birds" you'll see that many of them were considered 
separate species or subspecies 100 years ago.  Lillian's (Eastern) 
Meadowlark, Woodhouse (Western) Jay, the various winter wrens, hermit 
thrushes, owls, and vireos were all recognized in the past, but 
disappeared when many species were "lumped" in the 60s and 70s.  Just as 
Northern Orioles returned to Bullock's and Baltimore, many of what we 
now consider single species could easily be considered 2-4 species, 
depending upon what criteria we decide to use to separate them.

You don't need $100 million to appreciate that many wide-ranging species 
vary across their ranges.  All you need to do is read the existing 
literature, go out in the field, and use museum collections to confirm 
your findings.  Anyone claiming that multiple bird species were hidden 
in plain view until this new technique arrived is ignoring the vast 
amount of detailed field work published by several generations of North 
Americn ornithologists and birders. 

Walter Wehtje
Columbia, MO

Robert Fisher wrote:

> Perhaps someone can enlighten us on how DNA is used to distinguish one 
> species from another. I assume that not every difference in DNA makes 
> two individuals belong to different species. For example, there must 
> be some variations of DNA between recognizable subspecies -- i.e. if 
> the larger, paler Ipswich Sparrow hatched on Sable Island did not have 
> somewhat different DNA from a smaller, darker mainland Savannah 
> Sparrow their appearances would identical. The old fashioned method of 
> distinguishing between species was to ask how often they interbred in 
> areas of sympatry. If we are to go by DNA alone, what amount (or what 
> kind) of difference in DNA is now sufficient to separate species (and 
> to predict that they will not interbreed)?
>
> Do we now call the White-tailed Ptarmigan on every mountain top 
> different species from those on every other mountain top because they 
> have been isolated from each other for many generations? Or is there 
> some way of using DNA to identify a genetic isolating mechanism, which 
> would keep individuals of one population from breeding with 
> individuals of another even population were they to occupy the same area?
>
> Bob Fisher
> Independence, Missouri
> [log in to unmask]
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*              Audubon Society of Missouri's              *
*                Wild Bird Discussion Forum               *
*---------------------------------------------------------*
* To subscribe or unsubscribe, click here:                *
* https://po.missouri.edu/cgi-bin/wa?SUBED1=mobirds-l&A=1 *
*---------------------------------------------------------*
* To access the list archives, click here:                *
* http://po.missouri.edu/archives/mobirds-l.html          *
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* To access the Audubon Society of Missouri Web           *
* Site:  http://mobirds.org                               *
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