[birdky] FW: [Fwd: [Va-bird] Black-capped Chickadees in northwestern Virginia (?)]
- From: Jackie Elmore <jackiebelmore@xxxxxxxxxxx>
- To: BirdKY BirdKY Listserve <birdky@xxxxxxxxxxxxx>
- Date: Fri, 7 Dec 2007 21:18:47 -0600
With recent sightings in Kentucky, should we consider this?
Jackie B. Elmore
near Stanford, KY
Lincoln County
Date: Fri, 7 Dec 2007 14:04:10 -0500Subject: [Fwd: [Va-bird] Black-capped
Chickadees in northwestern Virginia (?)]From: marcusb@xxxxxxxxx:
carolinabirds@xxxxxxxxxxxx the apparent southward movement of Black-caps this
year, the issue regarding separation from Carolinas in the field has resurfaced
in Virginia, as noted in the string in VA-BIRD. Another commentary and
reference below may be relevant to the complex situation in the southern Blue
Ridge of NC and TN.M SimpsonAdvance, NC---------------------------------
Original Message --------------------------------- Subject: [Va-bird]
Black-capped Chickadees in northwestern Virginia (?) From: Birdconsv@xxxxxxx
Date: Tue, November 27, 2007 5:25 pm To: va-bird@xxxxxxxxxxxxx
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Recently, there have been a number of postings concerning sightings of
Black-capped Chickadees in northwestern Virginia and some useful discussion
about how to distinguish them in the field. Unfortunately--and I hate to rain
on the parade--but that region is a documented zone of hybridization between
the subject species and the Carolina Chickadee. Work by Gene Sattler and
associates, most notably the paper published in The Auk in April 2000,*
demonstrate that a principal area of hybridization lies along the ridges that
form the western wall of the northern Shenandoah Valley. Based upon a series of
transects, especially one running northwest from Massanutten Mountain between
Woodstock and Edinburg to a point just northeast of Liberty Furnace, Sattler
and Michael Braun found that..."Genetic data revealed that at least 58% of the
birds in the center of each transect were of mixed ancestry and that
recombinant genotypes predominated among hybrids, demonstrating that hybrids
are fertile." In the case of the transect described above, that center lies
near Columbia Furnace on/near Little North Mountain. Moreover, their work
showed that..."patterns of morphological variation were equivocal regarding
introgression [hybridization] across the hybrid zone." In other words, there
was no useful correlation between appearance--as shown in bird guides--and the
genetic makeup of a given bird. The same situation obtained with song. The
bottom line, in non-scientific language, is that as you can't tell a book by
its cover, in this region you can't ID a chickadee by its appearance and/or
song.
These field studies were carried out during the breeding season, so are most
pertinent for that period. There is strong reason to believe that pure
Black-capped Chickadees do drift south or downslope into northwestern Virginia
in the winter as do siskins, Purple Finches, Red-breasted Nuthatches, and other
"winter birds." Accordingly, some of the chickadees we see in winter in that
area--and which look like black-caps--probably are indeed black-caps. The
problem is that short of genetic analysis we really can't determine which are
truly black-caps and which are hybrids. Indeed, in that area we face the same
problem with Carolinas, and some of the Carolina-looking birds we see in
northwestern Virginia are likely also hybrids.
My interest in this subject arose because I own property precisely in the zone
of greatest hybridization. That is the site where we participate in Project
Feeder Watch (since 1989) and, more recently, routinely submit data to eBird.
Feeder Watch has provided a "mixed" category since the inception and eBird has
just this fall added both a hybrid and a mix category, both of which we use all
year for lack of a better option. However, if it comes down to a Life Bird
call, it appears that there is no good (or legal) solution.
Based on recent history on this web site, I expect that this information will
probably annoy or even provoke some readers. All I ask is that you bear in mind
that I am only the messenger and have no axe to grind here.
With best regards to all,
Dave Davis
Arlington and Cedar Creek
* Morphometric Variation as an Indicator of Genetic Interactions between
Black-capped and Carolina Chickadees at a Contact Zone in the Appalachian
Mountains. Gene D. Sattler and Michael J. Braun. The Auk 117(2):427-444, 2000.
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