Thanks to Joe Coleman for posting the Cornell Lab press release on
this study of the shift of the Carolina-Black-cap overlap zone to the
north with changing winter temperatures. This is fascinating and
important work, and studies like it will help us all to better explain
and understand climate change. However, at the risk of being a bit of
a wet blanket, I have to admit feeling a bit of a shudder when I read
that eBird data was a significant component of the research. I am and
have long been a major supporter of eBird, and I have over 3100
checklists in the data base. Over half of these checklists are from
(or near) our property in Shenandoah County, Virginia, specifically in
the area that was originally studied in describing the hybridization
zone for these 2 species. Most of the early work was done by
Professor Gene Sattler, a frequent contributor to this list serv.
(Apologies if I spelled your name wrong; I didn't have a reference
handy when I typed this.).
Based upon my reading and communications with Prof. Sattler, I
concluded that it was not possible to reliably distinguish between
pure Carolinas, pure Black-caps, and hybrids in our reporting area.
Hence, almost all of our eBird and Feeder Watch records show "Carolina/
Black-capped Chickadee;" that is, a mix of the 3 possible genotypes.
The exception is a few reports of pure Black-caps during well-
documented irruption years for northern Black-caps, which are
distinguishable based on size and pattern. So, if the study is using
our data for where the hybrids are/were, and if other people are
reporting similarly--that is, using the "slash" type as the default
reporting type--then I have to wonder about the study's conclusions.
Put another way, we are still reporting our birds as Carolina/Black-
capped when, in fact, the introgression zone may have moved well
beyond our site over the years, and we may now have only Carolinas
(expect for some winters). I have considerable faith in the Cornell
folks, so I can only assume that they somehow took this into account,
even if the press release left it ambiguous. I certainly hope so, and
I look forward to learning more about the study in the coming months--
and to amending our reporting practice if that is called for.
Good birding and best wishes
Dave Davis
Arlington and Cedar Creek
