Thursday, May 23, 2013

Hybrid Chickadees: music from the contact zone

Here in the Cleveland area, we live in the land of the Black-capped Chickadee.


When I teach bird song classes or give programs in the greater Cleveland area and surrounding NE Ohio counties, theirs is the first song I present.  The Black-capped Chickadee song is a very clear, simple, two-note tune that most people have heard and can easily learn to imitate.


From around Canton south, the Black-capped Chickadee is replaced by its southern cousin, the Carolina Chickadee.  


They look very similar, and there is an obvious relationship between their songs.  The four-note Carolina Chickadee I typically hear resembles a Black-capped song with an additional high note added before each of the two primary pitches.  It's rather like an ornamented version of the simple two-note tune.  If I edit out those extra pitches, what's left is essentially...the Black-capped song.  Their calls are also similar, but the Carolina Chickadee calls sound like they belong to warmer climate birds - lighter, higher, and faster versions of those belonging to their northern relatives. I laugh with delight when I hear them!

Here is a Carolina Chickadee I recorded singing at the edge of the swamp at Killbuck Marsh Wildlife Area south of Wooster. 


South of Cleveland and north of Columbus is an interesting area where the two chickadee species coexist and occasionally hybridize.  This is called the contact zone, and the boundary extends from southern New Jersey west into the Great Plains.  According to David Sibley in the online version of the Sibley Guide to Birds, 

Hybrids may be fairly common in the contact zone (up to 2/3 of individuals in some areas) and may show any combination of features.  Many chickadees in that area are simply not identifiable.

Carolina's song is higher-pitched and more variable from two- to six-noted, often a three-noted "fee-bee-bee" very similar to Black-capped.  The so-called classic Carolina Chickadee song "fee-bee-fee-bay" is, year round, no more frequent that other variations, although Frank Gill (pers. comm.) reports that it is the most frequent song in spring, and Ward (1966) reports that the song is less variable near the contact zone than farther away from it."

(I've noticed that when I can actually see the spectrogram of a song, occasionally a three note song does indeed have a high fourth pitch present before the final lower note and we mere humans simply may not hear it.)

I'd read that when both species are present, hybrids may sing the songs of either one. I did not realize that hybrids might also sing songs that belong to neither species, but I had the opportunity to observe this first hand in the contact zone south of Akron.   

I had decided to go to The Wilderness Center in Wilmot, Ohio (southwest of Canton) to try to record Carolina Chickadees.  My work schedule does not often allow me to go as far south as Columbus to record them, and my previous Columbus-area recordings had been marred by car, truck, and air traffic noise to the point of being unusable. It seemed that The Wilderness Center would be a good plan.  It is a little south of Route 30, which is the unofficial dividing line of the chickadee species.  I decided to give it a try. 

When I asked at their education center about Carolina Chickadees, I was told that they have Black-cappeds, Carolinas, and hybrids - and that the hybrids could have some unusual songs.  Really?  Would I be so fortunate as to hear any?

Again from David Sibley:

Many individuals in and near the contact zone sing typical songs of both species, or sing the wrong song or abnormal songs...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 "hybrid" song.  (See the link below to read the entire fascinating article and Sibley's citations.)

The first song I heard may have been one of the Carolina options, though I am still learning their somewhat variable repertoire.  It was a four-note song, but the third note was not a high pitch.  There was an initial high pitch, a normal chickadee-range pitch, a pitch one step higher, then a return to the second pitch.  It was as if the first half of the song was Carolina and the second half Black-capped.


The next unusual song I heard was unlike any chickadee song I'd heard before.  It was a three-note song with all three pitches within a very close range. There were no little Carolina high-pitched grace notes, and the song had three clear pitches instead of the two expected notes of the Black-capped song!


I was fascinated, of course - and the next song was even more interesting!  I found and recorded another chickadee that sang a three-note song but would occasionally sing two or three additional repetitions of the last note.  Sometimes this bird sang just the last note as a  single pitch three or four times.  His delightful song was my favorite, and you'll hear him here with a Northern Cardinal as a duet partner.


The Black-capped/Carolina hybrid zone is gradually moving north, and Carolina Chickadees have been banded as far north as Geauga County.  I love both species and their songs, and now I know to listen for the possibility of unusual hybrid songs as well.

You can read much more about all of them, the contact zone, and see a zone map at http://www.sibleyguides.com/bird-info/black-capped-chickadee/black-capped-carolina-chickadee.  As for me, I'll certainly be making additional trips to the contact zone with my microphone!

 

3 comments:

  1. Hi Lisa! This is really great information! I'm a Ph.D. student at OSU in Columbus and I've been studying hybrid chickadee song for the past five years, mostly in eastern Pennsylvania (where I did my Masters work). The hybrid zone in Ohio hasn't been studied since the early 2000's and I'd love any data you have on the "mixed" songs you've recorded. We rarely get mixed song types any more at our field sites in PA... instead we have populations of "bilingual" hybrids that have a two-song repertoire containing perfect versions of both Black-capped song and the four-note high-low-high-low song of the Carolina Chickadee.

    If you have high-quality recordings of chickadees (and any other birds) I encourage you to upload them to Xeno-Canto (http://www.xeno-canto.org), a massive online database of avian sounds that is used by researchers and bird enthusiasts worldwide. There is no "official" place to put hybrid recordings, so you'll need to choose a species and then indicate probably hybrid origin in the subspecies field or in the notes. There are definitely no mixed songs in that database and I think the people there would be very interested.

    And I'll have to head over to The Wilderness Center with my microphone at some point!

    Cheers, Stephanie

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    1. Thank you, Stephanie! I will look into uploading to Xeno-Canto in the near future and I appreciate your suggestions on how best to do this. You are welcome to email me directly as well.

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