Date: 3/13/17 8:31 am
From: Alan Buriak <a_buriak...>
Subject: Re: Allegheny County - Chickadees
Sameer and PA Birders,


I have been one of the primary eBird contributors for the North Park area for the last 1-2 years, so I can speak to this topic.


First, if you check the map of the hybrid zone in the following link by David Sibley, it places North Park just north of the top edge of the zone, suggesting that pure Black-capped should be found there.

http://www.sibleyguides.com/bird-info/black-capped-chickadee/black-capped-carolina-chickadee/

<http://www.sibleyguides.com/bird-info/black-capped-chickadee/black-capped-carolina-chickadee/>However that article was posted in 2010, and the data used for the map was probably even older.


Pertaining to North Park, I have also absolutely observed that the chickadee situation there has become very muddled. I haven't paid that close of attention to how others are submitting them, but you will notice that for a couple years, I have been submitting all chickadees in North Park from Latodami Nature Center south as Carolina/Black-capped Chickadee. I observed a gradual intrusion of Carolina physical traits and vocalizations that made it clear to me that the hybrid zone had shifted north to engulf most of North Park. I do, however, still observe birds in the upper field area, at the northernmost part of North Park, that fit pure Black-capped Chickadee, and I regularly still hear Black-capped songs around the field. I think it is reasonable to say that the upper field is one of the last holdout areas of pure Black-cappeds in North Park, both because it is at the northernmost extreme part of the park, and also because it is at one of the higher elevations vs most of the park. Doing a quick check of the Latodami Nature Center hot spot, most of the recent checklists by people other than myself also report the chickadees as Carolina/Black-capped Chickadee, although there are a few that are listed as pure Black-capped. If you are seeing that most reports are pure Black-capped, that might be including older data. I actually made a comment in my January 13th checklist from Latodami Nature Center that speaks directly to this topic:

http://ebird.org/ebird/view/checklist/S33645124

I live in Gibsonia, to the east and a little north of North Park's latitude. I still have predominantly pure Black-capped Chickadees here, both in physical appearance, song, and call. I have never heard a Carolina song here yet, and can't see any obvious intrusion of Carolina physical traits. I have, however, noticed an ever so slightly quickened call pace of a couple single birds in the past few months, which makes we wary of the possibility of hybrid intrusion. With all my observations on the issue locally coming from my house and North Park, I personally would place the new top edge of the hybrid zone somewhere east of North Park and just west of the Gibsonia area. If you are wanting to go somewhere in Allegheny County where you should have no problem seeing pure Black-capped Chickadees, Harrison Hills County Park in Natrona Heights would be the place, as it is physically located at the far northeast corner of the county, the farthest point from the hybrid zone.

As for the birds you were seeing at North Park yesterday, I'd say that even though they are singing Carolina and have Carolina physical traits, they are likely hybrids. It seems certain that the hybrid zone has shifted north, but not far enough north to place pure Carolinas regularly in North Park, and as you alluded to, there is no reason to think that pure Carolinas would be irrupting northward at this time of year. Admittedly, I often do not attempt to discern individual birds within the hybrid zone, and often just submit them as Carolina/Black-capped Chickadee. Catching pure birds of either type irrupting northward or southward is dicey because the hybrids themselves are so variable. The fact that you heard so many Carolina songs is notable however, as I personally have still heard a lot of Black-capped songs even in the main part of the park. This may be a very recent development. You have certainly brought up a topic that I intend to keep a closer eye on. If anything I have said here is incorrect or misrepresented, somebody out there please call me out on it, but hopefully I have contributed something useful!

Good birding,
Alan Buriak
Gibsonia, Allegheny County


________________________________
From: Bird discussion list for Pennsylvania <PABIRDS...> on behalf of Sameer Apte <sameerapte1...>
Sent: Monday, March 13, 2017 1:20 AM
To: <PABIRDS...>
Subject: [PABIRDS] Allegheny County - Chickadees

This afternoon, Aidan Place, Jack Chaillet, and I birded North Park, where
we searched for Black-capped Chickadee (which Jack and I needed for our
county year lists). Despite the many reports of exclusively BCCH at this
location, every chickadee we found either resembled a pure Carolina or
predominantly resembled Carolina in phenotype. One chickadee at lake
elevation (970') had extensive white on the tertials and on the cheek
patch, and several chickadees at the Latodami Nature Center (1110') were
clear phenotypic hybrids between Black-capped and Carolina. Although we
heard many Carolina songs, we did not hear a single Black-capped song, and
many of the hybrids certainly appeared to be possible backcrosses with
Carolina Chickadees.

With BCCH reaching their furthest range southward around this time of year,
it begs the question as to why almost every chickadee seen in North Park is
identified as BCCH on eBird. Are most of these reports are from a higher
elevation, where pure Black-cappeds are certainly plausible? Are Carolinas
(which are expanding northward) being dismissed as the traditional species
of Black-capped at this particular location and in other places north of
the Allegheny River (which I believe has been the demarcation line for the
last fifteen years or so)? Or was our sighting just highly unlikely and
exceptional?

I'd love to hear thoughts and experiences from people in the Pittsburgh
metro area about this paradox -- it seems like chickadee identification is
a thing that comes up once in a while, but maybe not as much as it should
in an area smack dab in the middle (or maybe not anymore) of the
hybridization zone. Perhaps it would be constructive to conduct a sort of
informal census of areas north of the Allegheny River to determine the
current demarcation line and hybrid zone of this species in the area.

And if anyone has any clue what exactly those mutt chickadees in North Park
really are, please let me know.

Thanks and good birding,
Sameer Apte
 
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