Hi Folks!
I have looked at a lot of chickadees in Maryland over the years.? The main
hybrid zone is immediately east of Sidling Hill.? It is very narrow.? The first
ridge east of Sidling Hill is Long Ridge..I have never identified any chickadee
to species on Long Ridge.? East of that is another ridge..I don't have it's
name right here....and all of the breeding birds east of that are Carolina
Chickadees.
Carolina or Carolina-like chickadees are rare in Allegany County, with most
reports clustered near the Pawpaw bridge and Town Hill aquaduct.
I have also encountered probably hybrids on South Moutain north of I-70 and in
the Catoctins Mountains, but these are greatly outnumbered by Carolina
Chickadeees and may represent birds that have wandered south from the hybrid
zone in Pennsylvania.
Good Birding!
Jim
Jim Stasz
North Beach MD
jlstasz@xxxxxxx
-----Original Message-----
From: Sattler, Gene D. <gsattler@xxxxxxxxxxx>
To: va-bird@xxxxxxxxxxxxx
Sent: Mon, 10 Dec 2007 2:27 pm
Subject: RE: [Va-bird] Chickadee ID in VA
-----Original Message-----
From: Joe Coleman [mailto:joecoleman@xxxxxxx] ;
Sent: Monday, December 03, 2007 2:19 PM
To: VA-Bird; Sattler, Gene D.
Subject: Re: [Va-bird] Chickadee ID in VA
I'd like to thank Gene Sattler for his very int'd addition to this
string.
It is also nice to see VA-Bird politely discussing this kind of topic.
We don't seem to do it as much as some other birding list servers where
people politely question each other and share their knowledge.
For years I have followed with interest reports of Black-capped
Chickadee and hybrid chickadees in western MD on MDOsprey. Not
surprisingly there has been a great deal of discussion on Black-caps
and possible hybridization in the area where Carolinas and Black-caps
meet. If my memory is correct, it is pretty far to the west, near the
Allegany Co/Garrett Co line. Incidentally the MDOsprey archives are
available online & are easy to search for anyone who wants to see what
they have to say on this topic.
To my knowledge the hybridization zone in VA isn't in the Shenandoah
Valley, itself, but up on the edge of the Allegany Plateau. I was
pretty sure that virtually all the chickadees that regularly show up in
the Valley are Carolina Chickadees. Perhaps some of our top long-time
Valley birders like John Spahr, Gene Sattler, and Rob Simpson could shed
some light on this? My memory also tells me that this is true for the
counties in the West VA Panhandle
and esp. Jefferson County. The official bird list for Cacapon Park
near Berekeley Springs (pretty far west in the Panhandle) lists the
Carolina as the resident species...
Best, Joe Coleman
near Bluemont, Loudoun Co
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As a continued follow up to this chickadee ID thread I wanted to respond
to an interesting issue that came up in this post by Joe Coleman. That
is, where is the zone of hybridization between Black-capped and Carolina
chickadees in northern Virginia (or elsewhere)? Joe conjecture is that
the hybridization zone (in northern Virginia) is at the edge of the
Allegheny Plateau, as opposed to in the Shenandoah Valley itself.
Actually, if my understanding is correct, the Allegheny Plateau, a
subset of the Appalachian Plateau, only extends into Virginia in far
southwestern Virginia. So the chickadee contact zone would actually be
considered to be located where the Ridge and Valley Province, which is
east of the Allegheny Plateau, meets the Shenandoah Valley. So the
question is whether the zone of hybridization between these two
chickadees is indeed at the western edge of the Shenandoah Valley, where
it meets the Ridge and Valley Province, as opposed to in the Shenandoah
Valley itself. The answer can be either yes or no, depending on your
perspective.
Joe is right in the sense that the contact zone, or the center of the
hybrid zone, is where the Ridge and Valley Province of the Appalachian
Mountains meets the Shenandoah Valley. This would be evident by
surveying chickadee songs throughout this region. In the Shenandoah
Valley you will almost assuredly hear only carolina songs. And on top
of Little North Mountain, the first mountain or ridge of the Appalachian
Mountains west of the Shenandoah Valley in Shenandoah County you will
probably hear only blackcap songs (see page 73 of the Virginia Atlas and
Gazetteer). Only if you go to this interface, basically on the east
flank of Little North Mountain, and along the bottom of stream valleys
that come down out of the mountains into the Shenandoah Valley, might
you hear some unusual chickadee songs, or bilingual chickadees that can
sing both species' songs'.
The location of the chickadee contact zone in this area, as well as
throughout the rest of the state, is also reflected in the range maps
published for Black-capped and Carolina chickadees by the Virginia
Department of Game and Inland Fisheries and the VSO as part of the
Virginia Breeding Bird Atlas Project, run between 1985 and 1989. These
maps are essentially based on just such a vocal survey done throughout
the state, conducted by all of the many birders who took part in atlas
project.
Now I will argue, however, that the hybrid zone is considerably more
extensive than such a vocal survey would indicate. To help illustrate
this point I am going to refer to an online copy of a song paper that
the VSO has graciously posted on their website (www.virginiabirds.net).
This paper was published this summer, and analyzes the same chickadee
populations as the morphology paper I referred in my earlier email
today, and which is also posted on the VSO website. This song paper
also makes use of the same genetic markers that were used in the
morphology paper.
Fig. 1 shows the approximate location of the populations analyzed. I
will be referring to the five populations forming a transect or line
across the hybrid zone at the northern Virginia portion of the zone
(VA1-VA5). VA2 and VA3 straddle either side of the contact zone. VA2
is located primarily on Great North Mountain in George Washington
National Forest, within Shenandoah County, although some of the birds
sampled were also on its eastern flank. VA3 was located in the
Shenandoah Valley in Shenandoah County. As noted above, birds in VA2
sang blackcap song, expect for a small proportion of birds down on its
eastern flank near the Shenandoah Valley floor, which also sang atypical
songs, or were bilingual. And birds in VA3 sang carolina song, except
for one or two birds at the valley's very western edge against the foot
of first ridges that sang blackcap songs (see Fig. 4 and Table 2).
Based on these vocal data, it would be reasonable to conclude that there
are a small proportion of hybrids at the western edge of the Shenandoah
Valley, along the flank of Little North Mountain and other ridges that
meet the Shenandoah Valley. One would also likely conclude that birds
on top of the ridges were blackcaps, and birds down in the valley
immediately away from the mountain's flank were carolinas. As Table 1
shows, however, these conclusions would be wrong. Genetic analysis
showed that 45% of the birds in VA2 were hybrids, and 62.5% of birds in
VA3 were hybrids. As emphasized in my earlier email today, to say that
these birds were hybrids does not mean that they were all first
generation (F1) hybrids. The majority were later generation or
"backcross" hybrids, as F1s are not sterile as is the case with mules.
(Keep in mind that this is all based on birds during the breeding
season, and does not reflect the situation in some winters when some
blackcaps could be present as a result of an irruption).
A central conclusion of this paper, then, is that song is not a reliable
indicator of the genetic interactions going on between these two
species. That is because there is a strong learned component to the
development of their song. These chickadees are similar enough
genetically that pure blackcaps, carolinas, and hybrids can each learn
to sing accurate renditions of either or both songs. This had been
shown earlier in a laboratory study (see Kroodsma et al. 1995 reference
in the song paper).
The take home message, then, is that just as analysis of morphology in
the earlier paper indicated that birds near the contact zone are not
technically identifiable without genetic sampling, the same is true with
respect to identifying birds near the contact zone on the basis of the
song they sing. For example, many of the birds in the Shenandoah Valley
that are singing good carolina songs are in fact hybrids, and many of
the birds on Great North Mountain and beyond it that are singing good
blackcap songs are also in fact hybrids.
Notice, however, that I did not say that some of the birds in the
Shenandoah Valley are blackcaps, or that some birds on top of Great
North Mountain were carolinas. We did not find that to be the case.
That is one of the fascinating aspects of these birds' interactions.
There is apparently enough of a difference in these birds' physiology
that the blackcaps are more competitive at the higher elevations/more
northerly latitudes, while Carolinas are more competitive at the lower
elevations/more southerly latitudes. This difference as you would
probably guess likely relates to temperature, although this has not been
proven.
As I concluded in my earlier email of 11/29, the presence of many
hybrids at the contact zone does not mean that we as birders should
throw up our hands and just call any chickadee in the contact zone
"chickadee sp.", or chickadee not identified as to species. It is still
useful to note the identity of chickadees here on the basis of the
species song that is typically heard in the area, as this accurately
reflects the position of the hybrid zone.
As an example both of the usefulness of paying attention to song, and of
how ecology plays a part in these chickadees' distribution, I'll
conclude by drawing attention to one particular bird encountered in our
survey in Virginia. This bird was found in VA4, which was located in
eastern Shenandoah County on Powell Mountain (page 74, B1 of the
gazetteer). As Fig. 4 of the song paper indicates, a couple of birds in
this population were heard singing a blackcap song. One of these two
birds was analyzed morphologically, vocally, and genetically. Based on
its wing length, tail length and mass, it had the morphology of a
typical blackcap (Fig 3C of the morphology paper). Likewise, vocal
analysis indicated that its song was that of a typical blackcap (data
not shown in the song paper). And based on our four genetic markers, it
also appeared to be a blackcap. This is probably a bird, then, that
dispersed across the Shenandoah Valley and settled at this higher
elevation. Occasional Black-capped Chickadees probably do this on the
Blue Ridge also, just to the east of Powell and Massanutten Mountain, as
birds singing blackcap song during the breeding season are sporadically
reported from the Blue Ridge. It is probably a fairly rare event,
however. The proportion of hybrids estimated in VA4 was 28.6% (Table 1
of the song paper), considerably lower than the 62.5% found in the
Shenandoah Valley below. And without genetically analyzing such a bird,
there is no way to be 100% sure that it is a pure blackcap, as opposed
to say a hybrid from the contact zone that has learned the song of
blackcaps, and then dispersed into the range of Carolinas.
The distribution of these chickadees in Virginia makes for an intriguing
subject, and birders can help add to our knowledge by becoming familiar
with the general location of the contact zone and taking note of the
songs heard in its vicinity in different locations. I hope to put
together a little more formal written summary on these chickadees'
distribution in Virginia soon for Virginia Birds.
Good birding,
Gene Sattler
Lynchburg
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