One thing birders tend not to keep in mind are Ring Species and how
they affect "discrete naming" or classification of birds to a species
or subspecies. Sometimes you just can't do this.

<http://en.wikipedia.org/wiki/Ring_species>

> In biology, a ring species is a connected series of neighboring
> populations that can interbreed with relatively closely related
> populations, but for which there exist at least two "end"
> populations in the series that are too distantly related to
> interbreed. Often such non-breeding-though-genetically-connected
> populations co-exist in the same region thus creating a "ring".
> Ring species provide important evidence of evolution in that they
> illustrate what happens over time as populations genetically
> diverge, and are special because they represent in living
> populations what normally happens over time between long deceased
> ancestor populations and living populations.
>
> Ring species also present an interesting problem for those who seek
> to divide the living world into discrete species, as well as for
> those who believe that evolution does not create new species. After
> all, all that distinguishes a ring species from two separate
> species is the existence of the connecting populations - if enough
> of the connecting populations within the ring perish to sever the
> breeding connection, the ring species becomes two distinct species.
>
>


As you can see for birder who like to count say "subspecies" this can
be a problem. Even for those who just tick "whole species" it is a
problem e.g. the Larus gulls (Herring Gull and the Lesser Black-
blacked Gull) form a ring species in their distribution in a ring the
Arctic Ocean.

I'm sure you don't have to bird too long in the PNW before you find
out about the Western x Glaucous-winged hybrids which (I suspect) is
another example of a ring species. Townsend and Hermit Warbler's may
be another local example. Song Sparrows subspecies? House Finch
variability?

Richard Dawkins' "The Ancestors Tale" (in the Salamander's Tale,
p302-310) has a particularly nice non-technical write up of the
problem of ring species and discrete names using Ensatina salamanders
of California's Central valley. Worth a read.

<http://en.wikipedia.org/wiki/Ensatina>

The Ring species concept are something to keep in mind when you try
to name any subspecies or species that interbreed to form hybrids. It
should be mentioned a little more in field guides (rather than just
talking about the odd "annoying" exceptions).

On Apr 10, 2009, at 11:33 PM, Aquila Chrysaetos wrote:

> I rarely see Fox Sparrows in my yard, but there have been a couple
> around for a week or two. One has been singing this week. I have
> never seen one at a feeder until today and I was able to photograph
> it. Comparing the photos to Sibley's illustrations, I was unable
> to tell if it was a pale Sooty (Pacific) or of the Canadian Rocky
> Mountain race.

--
Kevin Purcell
kevinpurcell at pobox.com