Date: 11/15/20 10:53 am From: 'Jim Stasz' via Maryland & DC Birding <mdbirding...> Subject: Re: [MDBirding] Black-capped Chickadee?
I have been looking at chickadee in eastern Allegany County for a few years. Although I haven't done any genetic tests, I am fairly confident that almost all of the birds singing Black-capped Chickadee song between Sidling Hill and Town Creek are hybrids. Many have been photographed and entered into eBird: ¬†https://ebird.org/map/x00195?neg=true&env.minX=&env.minY=&env.maxX=&env.maxY=&zh=false&gp=false&ev=Z&mr=1-12&bmo=1&emo=12&yr=all&byr=1900&eyr=2020¬†Carolina Chickadees remain rare in Allegany County and need to be carefully documented.¬†¬†This year has already had a few Black-capped Chickadees from northern populations into the Piedmont. As winter progresses I expect we will get a better idea about the extent of the incursion.¬†¬†Jim¬†Jim StaszNorth Beach <MDjlstasz...>¬†In a message dated 11/15/2020 12:32:52 PM Eastern Standard Time, <wsyacy...> writes:¬†
Re vocalizations (thanks to D. Roberts for alerting me to this issue), from Sibley (https://www.sibleyguides.com/bird-info/black-capped-chickadee/black-capped-carolina-chickadee/):¬†¬†
"at a study site in Pennsylvania all birds sing Black-capped songs, and about 60% of those same birds also sing Carolina songs, even though genetic tests indicate all of these birds are hybrids and Carolinas (Curry). Thus, contrary to many published reports, song is of little value for identification within the contact zone, since a young chickadee there has the opportunity to learn both songs, or to incorporate elements of both songs into a ‚Äúhybrid‚ÄĚ song."
See the rest of the article and refs to see that the chickadees learn each other's song in the border regions so in Maryland, I don't think one can rely on songs.