Date: 3/14/17 4:24 pm
From: Scott Weidensaul <scottweidensaul...>
Subject: Re: Allegheny County - Chickadees
I don't have the reference handy, but my recollection from the work of one of Bob Curry's grad students a few years ago is that gene introgression from Carolinas into black-capped populations extended something like 50 or 60 miles north of the northernmost area (near Hawk Mountain at the time) where hybrids could be detected visually or by song. I have long felt that many birders in the middle third latitude of Pennsylvania are kidding themselves if they believe they can assign a firm species identification to their chickadees they see.

An additional twist; when the active hybrid zone moved into my part of southern Schuylkill County about 15 years ago, I was banding chickadees that looked like "pure" black-capped, and which sang black-capped songs, but whose measurements were clearly intermediate between the two species. As I read posts in this thread suggesting that a difference of a couple of miles (if I'm understanding the geography correctly) might mean the difference between pure CACH and BCCH, I am deeply skeptical, to say the least. I suspect that if we had the time and funds to sponsor a wide-scale DNA survey of the state's chickadees, we'd find that most of the birds south of I-80, especially at lower elevations, are some degree of hybrid.

Scott Weidensaul
Schuylkill Haven, PA

On Mar 14, 2017, at 7:07 PM, Rudolph Keller wrote:

> I live in eastern Berks Co., which was in the hybrid zone 10 or 15 years ago. I remember watching bilingual males sing both songs, an interesting experience, and seeing intergrade plumage. Now I hear only classic Carolina songs and the birds I see except in Black-capped irruption years (this is one of those years, but the irruption was small, as far as I can tell) are the small, dull gray birds with small bibs that you would expect to see where Carolina is the breeding species. Here, the hybrid zone has moved to the northern edge of Berks and into Schuylkill Co.
> Rudy Keller
> ----- Original Message ----- From: "Dnadeb" <dsg4...>
> To: <PABIRDS...>
> Sent: Monday, March 13, 2017 8:16 AM
> Subject: Re: [PABIRDS] Allegheny County - Chickadees
> Good observation. A couple of years ago Robert Curry from Villanova spoke about his research on this very topic. With Carolinas moving north the interbreed sings nearly exclusively the CACH song. You are correct. Birders can be more observant as this moves across the state. We have not noticed it yet in Central PA.
> Deb Grove
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