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On Carolina Black-capped Chickadees

August 13, 2010

As the eBird reviewer for the state of North Carolina, I’m often in the position of making decisions as to the validity of difficult species.  This is generally not as hard as it sounds, and the vast majority of identification issues can be addressed in a few e-mails back and forth to determine the skill of the birder and the robustness of the sighting.  I’m not interested in judging birders or shaming their mistakes as much as getting the correct information in the database, and if that means invalidating a potential record based on simply not having enough information than I’d rather do that than allow a potentially shoddy record, and I try to be upfront about that.  I’ve outlined my own strategy for dealing with this stuff in a previous post.  The shorter version is that it’s not personal, it’s science.

For North Carolina the eBird review list is not terribly confusing, but the one species that I continually find to be the most difficult to ascertain its validity is one that is staggeringly common across much of its range.  So common in fact, that most birders don’t even give it a second thought, which is actually part of the problem. It’s the Black-capped Chickadee (Poecile atricapillus),  the little Parid admired for its tenacity and personality across most of the continent.  Well, except for the southeast corner, where it’s replaced by the extremely similar Carolina Chickadee (Poecile carolinensis), and therein lies the problem and the bane of the North Carolina eBird reviewer’s existence.  In fact, there’s little you can do that’s more likely to get an immediate response from me than report a Black-capped Chickadee in my state.

There’s a stretch of high mountains in the far western part of the state that historically has been home to an isolated population of Black-capped Chickadees.  It’s notable not only for being the southern terminus of the species’ range in the eastern US, but also because it’s a full 200 miles farther south than the next population, a not unsubstantial distance for a bird that’s scarcely 6 inches long and hardly known as a dazzling aerialist.  This isolation will be more notable later in this post, but it’s enough now to emphasize that the birds that live in far western NC and far eastern Tennessee have very little contact with, and are therefore generally genetically isolated from, the greater population of Black-capped Chickadees across the rest of the continent.  This distinction is unique among the group of primarily boreal-nesting species, notably Red Crossbills, Saw-whet Owls and several nesting warblers, whose ranges extend south along the high ridges of the Appalachians where the ecosystem is significantly different than the rest of the state.

This is very much an island of atricapillus in a vast sea of carolinensis, and as such, there has always been a great deal of confusion as to how the two birds interact with each other. Confusion that often plays out on the eBird filters for the state.  Adding to this, I’ve found that there’s very little information available online about the interesting story behind Black-capped Chickadees in North Carolina, so in the interest of dispersing some of that fog and perhaps making my job a little easier as a reviewer, here’s the scoop on this species and its history in the state.  It may well be only relevant to a few, but it’s a cool story nonetheless.

In the 1940s, this unique population was well studied by James Tanner (yes, that James Tanner) which culminated in his 1952 article in the Auk called, appropriately, Black-capped and Carolina Chickadees in the Southern Appalachian Mountains (.pdf).  Tanner spent several years in and around the recently dedicated Great Smoky Mountains National Park trying to figure out exactly where the line between Carolinas and BCs occurred and how the two species interacted with each other, something we’re still trying to get a handle on more than 50 years later, but I digress.  As you might expect, he got some interesting results, not least of which is that these BCs average smaller in size than the birds in the next closest population in West Virginia*.  They were actually closer in size to Carolinas, which you would expect in a largely isolated population so far south (so says Bergmann’s Rule).  This was also one of the first published reports of the two species regularly copying each others’ vocalizations, and Tanner noted on several occasions individuals of both species switching back and forth.   Even given their similar size and penchant for vocal impersonation, there was no acceptable amount of hybridization between the two species.  It may be exceedingly difficult for birders to tell the two species apart in the field, but the birds seem to manage it just fine.

*Update: While Tanner compared the size of the NC BCs to birds from the West Virginia area, this includes Appalachian Virginia, where the closest population occurs.

Additionally, and perhaps most pertinent to the birder who wishes to find them, BCs in North Carolina nest exclusively at elevations above 400o feet, where they’re highly associated with remnant stands of Red Spruce, Balsam Fir, and, especially, Yellow Birch (Betula lutea).  In fact, Tanner states that the BC nests that he found were exclusively in Yellow Birch cavities and the birds would even forgo nest boxes in areas where Yellow Birches were prevalent.  On those mountains where BCs were present, Carolinas would not nest above that seemingly arbitrary 4000 feet barrier, despite the two species nesting as close as one mile of each other on occasion.  However, and this is a crucial point, on mountains where Black-capped Chickadees are historically absent, Carolinas nest all the way up to 5000 feet.  So there is clearly some sort of competition between the species, though altitude alone is not the only determining factor predicting which Chickadee you’re likely to find.  It is interesting that Tanner notes that nearly all the high mountains where BCs are replaced at altitude by Carolinas had their native vegetation, including stands of Spruce and Birch, logged over in the 1920s.  This includes Mount Mitchell, which at 6600 feet is the highest mountain in the eastern US, and while having nesting populations of other boreal species like Winter Wren and Hermit Thrush, hosts only Carolina Chickadees.

This misunderstanding of the altitude rule is the one that generally trips birders up.  Many assume that every chickadee that they see, or hear, over a certain altitude is a BC.  Add to that the birds’ propensity for rather accurate depictions of the others song, and you’ve got a recipe for poor or absent follow-up on high-elevation Chickadees.  Too often I’m left with notes consisting of little more than “I was hiking above 4000 feet and I heard a Chickadee”, which of course, can’t be validated.  It gets worse when you realize that Tanner’s work, though amazingly useful, is more than a little dated. Like all ecosystems, the Appalachians are dynamic and much has changed since his time.

In the 1950s a little invasive insect called the Balsam Woolly Adelgid was discovered in the mountains of North Carolina where, over the next two decades, it proceeded to wipe out 90 to 99% of the area’s Balsam and Fraser Firs, leaving “ghost forests” on the top of many of North Carolina’s highest mountains.  As you might expect, the implications on the birds in these ecosystem was substantial, and a Purdue University study (.pdf) in 1990, 17 years after the adelgid arrived in Great Smoky Mountain NP showed significant declines in all boreal bird species, with the Black-capped Chickadee being particularly hard hit, to the point where at some historic strongholds, places where Tanner found populations of nesting BCs, the species was extirpated.  Consequently, populations of undergrowth loving species, like Eastern Towhees, Chestnut-sided Warblers and yes, the more adaptable Carolina Chickadee, took off.  The BCs were reduced to a handful of sites at best, and many in the NC birding community considered them to be completely extirpated from the state.

Now that 20 years have passed since the worst of the Adelgid breakout and some of the Fraser Fir forests have begun to recover, there’s evidence that Black-capped Chickadees are present in the state, but only definitively in four counties; Swain, Haywood, Jackson, and Transylvania, but whether they were remnants of populations that survived the Adelgid breakout or they’re re-colonizers from parts north is unknown.  There have been reports outside of these counties, but they are extremely rare and accompanied by lots of evidence.  It’s important to note that the two Chickadees can be fairly reliably distinguished given a good look.  The white fringes on the secondaries of the BC is an very good field mark in all seasons, though late summer molty birds can be confusing.  Black-capped Chickadee is an excellent bird in the state, but achievable in the right places, nearly exclusively in and around Great Smoky Mountains National Park.

Bottom line? Check your chickadees, folks.  And be ready for an email if you report one to eBird.

  1. August 13, 2010 8:30 am

    Great article!

    This is the bird-blogosphere at its finest.

  2. August 13, 2010 8:32 am

    Superb review!

    What is the reason for the 200 mile gap in BCCH range?

  3. Nate permalink*
    August 13, 2010 8:53 am

    @Corey- Thanks!

    @Nick- Tanner suggests that the BC Chicks need a series of mountain tops over 4000 feet in a tight cluster to sustain a viable population. The only place where that occurs in NC is around Great Smoky Mountain NP, and the next closest is in WV (Update: Probably closer to Virginia). They’re a remnant of the last ice age when the Spruce-Fir-Birch forest covered most of the southeast, but got stuck there when the glaciers receded and never were able to really close the gap because what high mountains that exist between are generally surrounded by lower mountains that are uninhabitable because they’d be in direct competition with Carolina Chicks.

    They had to have occasionally hopscotched back and forth in the past, but when you add in the heavy logging at the turn of the century and the adelgid issue, eventually all the good habitat on the tops of mountains between NC and WV was gone.

  4. August 13, 2010 9:20 am

    To think of BCCHs as so habitat-limited is bizarre to me, coming from upstate NY. Where do they transition from everywhere to only mountaintops? I’m guessing the boundary with Carolina.

  5. Nate permalink*
    August 13, 2010 9:46 am

    @Nick- Yeah, it’s wild stuff. I look at a place like north eastern Kansas where I was earlier this year, which is BC territory, and there’s absolutely nothing about it that looks different from CACH habitat around here. But there’s clearly something that prevents them from being in the same place at the same time, at least during the breeding season, they can form mixed flocks at lower elevations in the winter.

    It might be cool to look at areas all along the boundary to see whether the inter-species competition that prevents them from overlapping is roughly the same across the entire boundary or if it changes based on regional characteristics.

  6. Hugh permalink
    August 13, 2010 9:54 am

    I really like this post’s combination of present-day knowledge and historical detail. I hadn’t realized there was an isolated popn in North Carolina, so I went to check eBird data for Black-capped Chickadee. And, uh-oh, they’re reported all through the Appalachians in Virginia (eBird map: It still looks like the popn is disjunct through northwestern North Carolina, but the gap isn’t quite as big as you suggest (i.e., that the gap extends clear to West Virginia). So you’ve got me wondering, are there indeed some Virginian black-caps, or does the eBird Virginia reviewer need to read this post and then you guys can armwrestle about it? In any case, thanks for a cool post, I’m tweeting it.

  7. Nate permalink*
    August 13, 2010 10:20 am

    @Hugh- I would trust the Virginia eBird person generally. Tanner mentions West Virginia a lot, but there are almost certainly good populations in Appalachian Virginia too. It’s complicated further because in the high elevations in NC where historic pops of BC have been extirpated, there’s anecdotal evidence that the Carolinas still vocalize like BCs 30 years after the last BC bit the dust.

    So I’d say only some of those points in the extreme western part of the state might need some additional scrutiny, depending on the robustness of the reports, but that the rest are probably good. As you say, that’s still quite a ways from the isolated NC pops in Great Smokey Mountain NP.

    Update: Tanner had a chart in his paper where he compared NC Black-capped Chickadees to bird from the “West Virginia area”. I read that as only West Virginia, but Tanner notes that “The West Virginia area includes the Appalachians of West Virginia, western Virginia, western Maryland, and southwestern Pennsylvania”.

    That’s some area, Jim…

  8. August 13, 2010 12:06 pm

    Awesome post Nate. The Black-Capped and Carolina Chickadee problem isnt limited to North Carolina. Even here in NY (where there are no accepted records of Carolina’s), if you look at a map, the southern point of Staten Island (Conference House for those of you familiar) is nearly directly across the river from areas of New Jersey that have Carolina’s. There have been an increasing number of sightings, more heardings as several very reliable birders report hearing Carolina Chickadee song. Whether these are true Carolina’s or Black-Capped Chickadees returning north, is unclear.

    Whats also funny in New York State is both Boreal and Black-Capped Chickadee will be found with each other, often forming mixed flocks, especially in winter. Even on the higher mountains, there seem to be some overlap of the two (although Boreal will nest right to tree line), why can those two species co-exists well, while Black-Capped and Carolina’s can’t to the same degree? And what about those “dead zones” where neither chickadee is a regular? Fascinating stuff!

  9. Nate permalink*
    August 13, 2010 2:10 pm

    @Will- Thanks! You bring up a good point about the boundary lines elsewhere and I’m not aware of how birders in those areas handle the situation. Is there a issue with the species imitating each others songs or is each species associated with a certain habitat type or tree? I’d be curious to know.

    In Missouri, the boundary was roughly the Missouri River across the center of the state, but I’m sure elsewhere it’s not so cut and dried.

  10. August 13, 2010 10:04 pm

    Great post, Nate! I didn’t know about the remnant population of Black-capped Chickadees in the Great Smoky Mountains. Like Nick, I find the idea of Black-capped Chickadees being habitat specialists somewhat bizarre. The ones I’ve encountered occur in all sorts of habitats.

    I live on the Carolina–Black-capped border in New Jersey, so the identification problems are familiar to me. What I’ve found is that the chickadees in a particular location tend to be all the same species and the populations tend to be stable. For example, the chickadees around my house are consistently Black-capped, but if I go a little bit south, I start running into Carolinas. The border between the two species appears to follow the division between the Piedmont and Coastal Plain, though the species and geographic borders do not match exactly. One anomaly is Sandy Hook, which has Black-capped Chickadees even though the surrounding areas in Monmouth County have Carolina Chickadees. In the western part of the state, Carolinas have been found breeding north of what was traditionally believed to be their northern boundary.

  11. August 15, 2010 12:47 pm

    Off topic, but on the topic of North Carolina birds:

    I just happened to see that North Carolina has an extended crow hunting season (from August to the end of February) with NO BAG LIMIT. Yikes. Species of crows are not distinguished by the North Carolina Wildlife Resources Commission, so American Crows and Fish Crows are all “fair game.” It’s also okay to use electronic calls to hunt crows in the state.

    Details on the hunting regulations in North Carolina are @

  12. August 16, 2010 9:15 am

    One topic often discussed amoung michigan birders is the slow northern progession of Carolina Chickadees in Ohio. Although the rate is slow (I attempted to measure it using ebird, and came to the conclusion that it might be 1-2 miles/year), it is quite important, because the Carolina’s are curently 60 miles south of the michigan border. I am not sure of it is a consequence of climate change, or not, I actually found very little information about it

    Thanks for this excellent post!

  13. Nate permalink*
    August 16, 2010 10:16 am

    @John- Chickadees do seem to have exceptional site fidelity, which helps when you’re trying to put a name on them. Do you happen to find that certain plant types are generally present or absent in BC vs Carolina sites?

    @Spencer- Yeah, I knew that. It’s one of the fun things about living in the south. From what I gather, most crow hunting is done in the far eastern, very rural, parts of the state.

    @Laurent- Wow! Interesting stuff. It doesn’t surprise me that Carolinas are moving northward. I wonder if something similar is happening altitudinally in the Smokies.

  14. Jennifer W. Hanson permalink
    August 17, 2010 10:42 pm

    Hi Nate,

    Thanks for a well-done post. I used to live in north Jersey, where Black-caps reign, but now I’m solidly in the intergrade zone and routinely use “chickadee sp.” in CBC record-keeping. They are fascinating little creatures and too easily taken for granted.

  15. August 21, 2010 8:12 pm

    Very interesting stuff. Thanks for a great post.
    Only BCs around me…thank heavens!

  16. August 23, 2010 12:57 am

    Thanks for the thought provoking post Nate. Thank goodness in California we only have the Chestnut-backed Chickadee and the Mountain Chickadee and they are easily distinguishable.

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