Date: 3/17/17 9:45 am From: Alan Buriak <a_buriak...> Subject: Re: Allegheny County - Chickadees
I wanted to jump back in on this conversation with some observations that I just made this morning from my yard. First however, I wanted to thank everyone that has contributed to this thread and wanted to give my opinion on some of the points that have been brought up. I am certainly humbled by the level of experience and skill that is being added to this discussion.
First of all, I think the point that Scott Weidensaul brought up about Carolina gene introgression is important. This is something that we all should keep in mind, that indeed most of the birds that we are observing within any near proximity to the hybridization zone, even birds we feel comfortable with calling "pure", are likely some degree of hybrid. However I believe this level of thinking also applies to birding in general. We should all be mindful that dealing in absolutes with bird identification would indeed be fooling ourselves. Literally any bird that we ID could potentially have some degree of hybrid ancestry, that, absent DNA tests, would be impossible to discern. If I understand correctly, even in the face of DNA data, the division between some very closely related species can become arbitrary, going back to the very base arguments of what constitutes a distinct species anyways. However despite this problem, as Paul Hess and Barry Blust have stated, there is still much utility to observing and documenting observations of phenotype within and near the hybridization zone since these observations are the lion's share of the data that we have on this topic. I feel that this data, even with all of its shortcomings, can still be used effectively to approximate the movement of the hybridization zone, even if the "true" hybridization zone (based on gene introgression) is actually pushing many miles north of the observable changes in phenotype.
The other point that has been supported by many is that, as Matthew Webb said, there is no clear line to the hybridization zone. In my initial email I placed too much emphasis on trying to mark the exact northern edge, when in fact it depends on where you're at. Indeed somewhere between my house and North Park, observations do change from Black-capped to hybrid, but it is certainly not that simple. Paul Hess commented that he is observing hybrid characteristics as far northeast as Harrison Hills park, which supports this idea that pockets of hybrids get established far in advance of lingering pockets of Black-capped Chickadees. This is what I observed at the upper field in North Park, although as I mentioned in a direct email to Aidan Place and Sameer Apte, I haven't attempted to closely observe the birds there since fall, so this may have changed at that specific location. I remember now that I had been hearing Carolina songs in Cranberry Township over 2 years ago, which would indicate that hybrids had pushed well beyond North Park even when I was still observing "good" Black-capped birds at the upper field. I like Geoff Malosh's point about the southern edge of the zone too, and that pure Carolina Chickadees are heavily over-reported in that area, maybe even more so than pure Black-capped Chickadees on the northern edge. In theory, the southern edge would be even more difficult to pinpoint, both because Carolina Chickadee vocalizations have been proven to be dominant in some degree, and also because, as Geoff said, since the zone is moving north, it would likely leave in its wake a lingering pool of Black-capped genes. It makes we think that these lingering Black-capped genes could extend quite far south, back to the location of the zone many years ago, if it is true that the hybridization zone has been moving north for some time. As Geoff said, it is indeed a mess!
Now for what I observed this morning in my yard. The first bird I observed was good for Black-capped in all physical traits that I could see, and I measured this bird's call at just over 3 "dees" per second (quite slow). The second bird I observed also looked good for Black-capped and called at right around 4 "dees" per second, still easily in the Black-capped range. Additionally, one of the first two birds (not sure which) let out two song phrases, both fitting perfectly for the classic Black-capped song. However, seemingly right on cue for this discussion, a third bird entered the fray that I quickly noted was calling a bit faster. I calculated this bird's call at just barely under 5 "dees" per second. I got a very brief look at this particular bird and was able to observe its bib, which in my opinion, could not be considered good for Black-capped, as it was just too crisp with no visible downward protrusion on the sides. Unfortunately I did not get a good look at the wings, but I consider this bird to be one of the first clear hybrids that I have seen in my yard. I think that based on my observations, my neighborhood could very well be 100% hybrid by outward appearance and vocalizations in the next 1-2 years. For those wanting to know, my neighborhood is situated right off the east side of the intersection of Rt. 8 and Rt. 910 in Gibsonia, Allegheny County. I will continue to keep a close eye on the situation here.
On a side note, I was able to confirm this morning that the local pair of Red-shouldered Hawks that have nested previously in our neighborhood are indeed again nesting here. I observed both birds carrying sticks to the crook of a large tree overlooking the ravine only about 150 yards east of my yard. The nest is still in its early stage. The pair has built a new nest in a different location each of the last 3 years. I certainly feel very lucky to have such beautiful raptors nesting so close by.
There are some distant pictures of the birds and nest site in my eBird checklist, as well as comments about the chickadees:
Gibsonia, Allegheny County
From: Bird discussion list for Pennsylvania <PABIRDS...> on behalf of Matt Webb <matthewmichaelwebb...>
Sent: Wednesday, March 15, 2017 1:14 PM
Subject: Re: [PABIRDS] Allegheny County - Chickadees
This thread has, indeed, been very interesting to follow. For the past
four years, Bob Mulvihill and I have been banding chickadees (as part of
the Smithsonian Institute and National Aviary's Neighborhood Nestwatch
project) at numerous sites throughout the Pittsburgh region. We have long
talked about how we have been collecting data on these birds, and have the
ability to collect samples for genetic analysis, but we have not yet
At some sites over the four years, we've caught and banded birds that
measure/appear very much Black-capped, and the next year (and subsequent
years) we would only catch birds that measure/appear very much Carolina.
In the Pittsburgh region, the "hybrid zone" most likely covers our whole
area and measurement and appearance are not enough to go by, but I have
noticed that it is not as simple as saying "North of here, we'll only get
Black-capped..." etc. I've caught birds in some areas that appear and
measure very Black-capped, and then go several miles north of there the
next day and catch birds that only appear and measure Carolina. We do,
however, tend to see that birds in northerly parts of the region tend to
appear/measure Black-capped, and those in the south tend to appear/measure
Carolina, but it's never very clear.
When I say "measure", I'm referring to page 335 in Peter Pyle's 1997
Identification Guide to North American Birds. I recommend that birders
begin to carry this guide and a (small) wing rule when going into the field
to clear up any ID problems. I am, of course, kidding, but I just wanted
to say that even with the added ability to have the bird in-hand and
measure both wing and tail, there is no real clear "hybrid zone" line.
Also, to add an interesting note, just this past fall, we caught and banded
15 Carolina Chickadees at Powdermill Nature Reserve, the highest number
ever caught there. We have only sporadically caught and banded 1 or 2 a
year, if that, in the past.
Someone (hmmm...) should study this further!
Thanks and happy chickadee-ing,
Carnegie Museum of Natural History