Date: 3/15/17 9:41 am From: Barry E. Blust <barryblust...> Subject: Re: Allegheny County - Chickadees
Very interesting discussion. I'll add my two cents.
I live in Chester County, two miles from the Great Marsh where Bob Curry and his team has conducted a considerable amount of Chickadee studies. Although this is now squarely in the Carolina Chickadee breeding zone, it wasn't when the studies began. I try to scrutinize the plumages of chickadees in my area of southeast PA and, unless it's strongly suggestive of Carolina or Black-capped, I'll record it in eBird as Carolina/Black-capped. (My differentiation of the songs is very weak so right now I don't use that to ID down to species.) Of course including photos (or recordings) of individuals in eBird reports is helpful.
I know many birders who automatically assume and mark Carolina for this area. On the other hand there are others who just mark Carolina/Black-capped because they don't know the plumage or song differences or aren't willing to take the time to look & listen to each chickadee. That is their prerogative. And on the West Chester CBC, which I compile, I warn people to not assume all chickadees are Carolina. In fact this winter there's been a significant incursion of Black-caps in southeast PA, affording us the opportunity to compare individuals, but also increasing the chance to misidentify a bird that is a Black-capped for those who always report Carolinas.
Given that the visual and aural cues are not necessarily accurate indicators of which species is being observed it's still important to report these when possible. As I explained to a couple of people recently, I feel the reporting down to species by plumage (or voice) when possible, even if the genetics of the individual bird may be strongly mixed or even the opposite of the plumage and voice ID, is of value to whomever may choose to use this data for future studies. Simply assuming Carolina/Black-capped causes some information to be lost.
Many birders, particularly novices, are not aware of the possibility of two different species in the same area and of the hybridization issue. Making them aware of these things and of the challenges of identification can go a long way towards more accurate reporting even if it is coming to the realization that you may not know the ID every time and simply report Carolina/Black-capped.
Barry E. Blust 21 Rabbit Run Lane Glenmoore, PA Upper Uwchlan Township, Chester County <BarryBlust...>
"When we try to pick out anything by itself, we find it hitched to everything else in the Universe." -- John Muir
-----Original Message----- From: Bird discussion list for Pennsylvania [mailto:<PABIRDS...>] On Behalf Of Paul Hess Sent: Wednesday, March 15, 2017 10:25 AM To: <PABIRDS...> Subject: Re: [PABIRDS] Allegheny County - Chickadees
As others have already said, we all owe thanks to Sameer Apte, Alan Buriak, Aidan Place, et al. who have posted important comments on the Allegheny County chickadee situation. They are all correct. Too many chickadees are being identified as Black-capped when they are actually hybrids or perhaps even "good" Carolinas. The problem is that many birders don't realize how swiftly the northern Carolina limit has advanced during the past few decades.
This has been a continual problem with the CBC, the breeding bird atlas results, and other reports since at least the early 1980s. Long before that in 1940, even the great W.E. Clyde Todd admitted in Birds of Western Pennsylvania that, early on, he had been not fully aware of Carolina Chickadees' distribution in southwestern Pennsylvania. (So, maybe we shouldn't feel too embarrassed.)
For now, I have an important caveat about the northeastern corner of the county. It is no longer strictly Black-capped country. I live in Natrona Heights, about 3 miles south of Harrison Hills Park. The chickadee hybrid belt has clearly advanced north into to my neighborhood during the past two years. It is a fascinating continuance of the range advance, and I now regularly hear vocalizations and see plumages that represent apparent intergrades by plumage and sound.
During the past year I have also observed and heard apparent intergrades at Harrison Hills Park. Birders should no longer to automatically consider all chickadees to be Black-capped there. I would love to know what you see and hear. I've birded at the park regularly and often since 1970, and the chickadees are now among the most interesting birds to watch. In addition, I've heard for several years that there is an isolated pocket of "good" Carolinas north of the park near Freeport at a low elevation along the Allegheny River, but I have never had a chance to check it out.
There are many weird plumages and songs as the contact zone moves north in the county. One of the classic intergrade vocalizations I often hear in my neighborhood is a four-note DEE-de-de-de, as reported during intensive surveys of the contact zone in southeastern Pennsylvania by Bob Curry and grad students at Villanova. Deb Grove and Scott Weidensaul mentioned those studies in their recent posts. Others have pointed out that a chickadee may look like one species but sing and call like the other.
This whole Allegheny county phenomenon was first recognized in the early 1980s when Kenneth Parkes, late curator of birds at the Carnegie Museum, and two brilliant young birders named Bob Mulvihill and Ted Floyd reported an advance of Carolinas into the Pittsburgh area in the Audubon Society of Western Pennsylvania Bulletin, I think in 1983. Today's young birders are clearly on the same observant path as Bob and Ted were in their teens.
I wrote an extensive analysis of the northward Carolina advance in southwestern PA particularly in Allegheny County between 1974 and 1994, submitted it to the Wilson Bulletin for publication, but priotrities intruded and I never got around to making the reviewers' requested changes. The data suggested that the northward movement of the hybrid belt was occurring at about a mile a year. That was approximately the same as the Curry teams' studies found in southeastern PA.
The true width of the overlap and active hybrid belt is unknown in southwestern PA; it probably fluctuates. Neither is the distance of decreasing genetic introgression past the active zone known. As Curry and his associates pointed out in their exhaustive research, genetic signatures of both species occur many miles from the center of the contact zone in southeastern PA. The same thing is likely true in southwestern PA, and I have long wished someone with such research interest and resources as Curry's would study the hybrid zone in our southwest.
This should not discourage birders from contributing to our knowledge by their eyes and ears. I would elaborate on an important point Geoff Malosh mentioned. In the absence of genetic data, we can still help to track the hybrid zone's movements, at least in general and importantly not only in the northern areas but also in the southern areas of the contact zone, by carefully studying every chickadee's plumage and song. In the absence of genetic evidence, as the Carolina range limit advances and the Black-capped range retreats, the only way we can have any idea what's going on is by looking and listening - and reporting as much visual and vocal evidence as possible.
Meanwhile, I have a one-foot-high box of chickadee references and my own past findings if anyone is interested in having it.