Hi Tweeters,

Being curious, I checked out D.W. Johnston's book (The Biosystematics of
American Crows, 1961), and reviewed his discussion of "The 'Corvus caurinus'
problem" as he puts it. It is important to note, I think, that he was also
in favor of lumping the AMCR and NWCR, after both a review of museum
specimens and his own field observations. Since wing and tarsus measurements
are useless to those of us watching the birds in the field, I paid special
attention to his remarks on habitat, habits, and voice. Interestingly, he
observed several individuals in and around Seattle give both a low-pitched
"grar-r-r", which is associated with the NWCR, as well as the higher-pitched
"gaw" which is associated with the western subspecies of AMCR
(C.b.hesperis). So it is obvious that some birds, especially in central
Puget Sound, can appear to be either. (Having moved here from Wisconsin a
couple years ago, I can definitely say that all of the crows in Western
Washington sound way different from Eastern Crows, regardless of what calls
they are giving. So all the differences that we are talking about here are
already small when compared with the larger continental differences that
AMCR display.) Johnston also heard that low-pitched "grar-r" call all the
way to the edge of the Cascades, especially in river valleys. He notes that
in Alaska, where the caurinus type is much easier to seperate from inland
crows, the mountains form a pretty clear boundary right along the coast, and
therefore the coastal crows don't have much chance to mix with inland
crows. Here in Washington, especially since forests have been cleared, that
barrier is not as prevalent, which is likely why we see the transition here.
As far as measurements go, Johnston also points out many of the museum
specimens that had previously been used to distinguish one type from the
other were either not sexed, or were 1st year birds, which cannot reliably
be compared with adults.

So, armed with that evidence, and barring any future genetic evidence to the
contrary, I am also be in favor of lumping these two species. In my opinion,
populations like this, which show an obvious latitudinal cline in their
charcteristics, with no clear line of seperation, and which commonly produce
viable offspring in a region of intergrades/hybrids, should not be
considered different species.

For the time being, I have been recording any crows I see near Puget Sound
or the Strait of Juan de Fuca - especially here in Seattle - as
American/Northwestern Crows (on eBird lists, that is). It's disappointing
that I can't tick off two different species on my lists, but
coming from a scientist's perspective, I know that it's always better to be
transparent about one's uncertainty. The folks at Cornell can always sort it
out later :-)

-Michael Schrimpf (Seattle - UW School of Fisheries)



On Mon, Dec 28, 2009 at 3:57 PM, Eugene and Nancy Hunn <
enhunn323 at comcast.net> wrote:

> Tweets,
>
> We've been round and round on this crow thread over the years. I've lived
> in and near Seattle since 1972 and have yet to be convinced that there are
> two distinct populations of crows in western Washington, certainly not since
> Euroamerican settlement, land clearing, and the construction of highways
> that now provide easy passage to crows across the cascades and up and down
> the coast. There are no physical or ecological barriers that might separate
> two crows and there has never been an obvious contrast in morphology,
> vocalizations, or behavior between interior and coastal crow populations.
> Also, it has never been made clear where the division between Northwestern
> and American crows might have been on the outer coast, as there are crows
> all up and down the coast from Alaska to California and probably have been
> so for centuries, with no obvious ecological barrier between Grays Harbor
> and Cape Flattery. Do Oregon coastal crows avoid foraging on the beaches?
> Yet no one has suggested that they are Northwestern Crows. I would be
> surprised if crows anywhere were so rigid in their behavior as to pass up an
> inviting food supply, on the beach or otherwise.
>
> The idea that there are two crow species here has not always been the
> preferred opinion, as Dawson in _The Birds of Washington_ (Dawson & Bowles,
> 1909) dismissed the notion that the Northwestern Crow was a good species
> analogous to the Fish Crows of the Atlantic Coast. He was subsequently
> overruled and in the current splitter-dominated climate the burden of proof
> is on those who would lump the crows, despite the lack of any convincing
> evidence that two species are involved.
>
> Not that the issue hasn't been carefully studied. D. W. Johnston published
> an analysis of North American _Corvus_ populations (_The Biosystematics of
> American Crows_, UW Press, 1960) and concluded that the crow populations in
> western Washington varied clinally in all relevant measurements between
> "typical" Northwestern Crows on Vancouver Island to "typical" American Crows
> along the lower Columbia River. He compared a large number of museum
> specimens from documented breeding populations. Of course, that was before
> systematic studies of vocalizations and DNA.
>
> For someone used to east coast crows ours will seem quite different, but
> one would note the same for our Song Sparrows, to mention just one example.
>
> I missed the WOS presentation by the UW researchers a couple of years ago,
> but apparently they found limited genetic contrasts between Seattle crows
> and Vancouver Island crows, less than what one would expect if two species
> were involved.
>
> Gene Hunn
> Lake Forest Park, WA
> enhunn323 at comcast.net
>
>
>
>
>
> --
> Michael Schrimpf
> Graduate Student
> School of Aquatic and Fishery Sciences
> University of Washington
> Box 355020
> Seattle, WA 98195-5020
> Tel: 206-221-6904
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman1.u.washington.edu/pipermail/tweeters/attachments/20091231/6ca7e483/attachment.htm