Sandy,
At Basye, three miles or so from the Shenandoah Valley and in a lower
elevation river valley, a fair number of the chickadees are likely to be
hybrids. That is a reasonable statement because at Wolf Gap, about 10 miles
NE of Basye, and about the same distance from the Shenandoah Valley, genetic
screening has estimated the proportion of hybrids there to be about 35%. At
Basye you might even occasionally encounter some abnormalities in song, such
as an occasional bilingual bird, even though Blackcap might be its
predominant song. But a lot of the chickadees there are also likely to be
pure Blackcaps. You just won't be able to tell which are which, either by
appearance or by song, regardless of what it sings. A few miles to the west
of Basye, up on the top of Great North Mountain, bordering West Virginia,
there would almost certainly be only Blackcap song heard, and I think any
birder would consider the birds there to be Blackcaps, even though it is
probable that genetic screening would show a small percentage of hybrids to
be present technically (that is backcross hybrids with a low percentage of
Carolina Chickadee genes, as opposed to first generation F1 hybrids). If
you wanted to be as sure as you could without the use of genetic markers
that a bird singing a Blackcap song in Virginia was really a "pure" Blackcap
you would probably pick the highest elevations of Highland County, although
no genetic screening has been done there. But from a birding perspective,
it is reasonable to call chickadees Blackcaps throughout most of the Ridge
and Valley Province, as long as you were not within perhaps 3-5 miles of
known Carolina singing populations, or hearing any Carolina song in that
population.
Gene Sattler
Lynchburg, VA
-----Original Message-----
From: Sandy Cash [mailto:scash@xxxxxxxxxxxxxx]
Sent: Tuesday, May 21, 2002 11:38 PM
To: va-bird@xxxxxxxxxxxxx
Subject: [va-bird] Black-capped/Carolina line of demarcation
Hi all,
I know that the border between Black-capped and Carolina
Chickadees is less of a border than a long zone of mixing and
intermingling, a sort of genetic DMZ...but are there areas of VA in
which one can be reasonably certain that what one sees is a Black-
capped? For instance, what about Great North Mountain, west of
Basye (Shenandoah County)?
I'm asking b/c I remember a recent post on the subject of genetic
markers for these species, and as Black-cappeds are *very* hard
to get in NC, even in the high mountains, I thought I'd see whether
the area around my mother's place (in Basye, surprise) might be a
place I could snag these.
Best to all,
-Sandy
--
Sandy Cash
Durham, NC
scash@xxxxxxxxxxxxxx
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