Tuesday, October 12, 2010

Phantom Followup: Bachman's Warbler

In the interest of my suggestion to "put the phantoms back on our birding radar," I'll spend a little time on the other one that is a swamp bird, Vermivora bachmanii. The prospects for this species' continued existence are also debated, though with much less venom than in the case of that large woodpecker. The last undisputed sightings and photos are significantly more recent; however it is also a shorter-lived species. Still, many of the arguments about large areas and small numbers of birds apply here as well and could have allowed a tiny relict population to be missed.

Bachman's Warbler was never a well-known species. Its breeding range was apparently spotty and very poorly characterized even before the population crashed precipitously. It spanned at least from Missouri and Louisiana to South Carolina and possibly Virginia. Migrants were seen in Peninsular and insular Florida in early spring and late summer (March-April and July-August), a migration pattern shared with many birds that nest in the Deep South and winter in the Antilles.

To understand this bird you should put it in its biological and ecological context. V. bachmanii is perhaps best viewed as part of a trinity of three very closely-allied buzzy-voiced brush-loving species of Vermivora, the other two being the Blue-winged and Golden-winged Warblers. These three birds are quite similar in size, structure, voice, and apparently habitat preferences as well. They essentially form a latitudinal gradient: Bachman's in the southern bottomlands, Blue-winged in the mid-latitudes and mid-elevations, and Golden-winged farthest north and highest up.

Many have the impression that the Bachman's was a deep swamp bird of the forest primeval. But it appears that, like its buzzy brushy brethren, it was actually a bird of gaps, edges, and early-mid successional habitats within the general forest mosaic. The famous I'On Swamp where it was last documented nesting had been a rice field a few decades before the warblers were first found there. By the way, most of you probably don't know that "I'On" is just a folksy colloquial spelling of the non-rhotic Low Country pronunciation of "Iron" -- "AH-uhn." Bachman's two primary vegetation associates appear to have been cane (Arundinaria gigantea) and blackberries; it seems to have been much less particular about the overstory trees. One might hypothesize that its true breeding range once spanned nearly the entire distribution of Arundinaria, which covers most of the coastal plain and many river bottoms extending into the uplands as well. Though it had more of a preference for, or at least a tolerance of, more forest canopy than do the Blue- and Golden-wings, the critical factor is still gaps, edges, and early successional components creating the mandatory dense understory.

The successional - gap dynamics aspect of Bachman's Warbler habitat has a major implication for anyone interested in where the species might still exist: Forget about the detailed locations where it was previously found. Would you look for Blue-wing in the same spot one was found 40 years ago? Of course not. The habitat is almost surely no longer suitable. So in the case of the Bachman's, forget the I'On Swamp, forget the Congaree. If there are any out there they are much more likely to turn up in some entirely unexpected brushy spot just about anywhere in the southeast than they are to be found in these historical spots. Folks just need to keep their eyes and ears open all through the region.

V. bachmanii is of course a warbler, and we all know how to find warblers: with our ears. Like any bird of deep cover, knowing the sounds this species makes is critical to having a chance of locating any that might still exist. Vocally, Bachman's Warbler is also closely allied to the other two Buzzy-Brushies. The good folks at the Macaulay library have compiled and cleaned up the entire collection of known sound recordings of the species into one 6 minute clip -- I'd wager that far fewer people have committed this sound bite to memory than have been imprinted on the Singer Tract Ivorybill audio. It has often been described as resembling the songs of a Northern Parula; but if you listen to it in the context of the Buzzy-Brushy Trinity the resemblance in quality to the Blue-wing and Golden-wing is very close. Only two song types for the Bachman's are documented; the other two buzzy-brushies have quite a variety of alternate songs so it is very likely that the Bachman's repertoire is larger than what you hear in that audio clip. But it is also likely that the dry thin buzzy Vermivora quality is consistent and characteristic.

To help get a better sense of the nature of the Bachman's Warbler songs, I have compiled a few examples of songs from the Parula and the other two brushy-buzzies for comparison. I'll be referencing sonograms here; but in the real world you will be using your ears not a spectrograph so listening to and studying the sound clips is the most important thing. For reference, here are sonograms of the two documented song types of the Bachman's Warbler:

It's just a surmise, but as the first song came from a presumably unmated bird in Virginia while the second was from a bird on territory in an active nesting area in South Carolina, I'd think it likely that the top one represent the "primary" or "type I" song while the second represents an "alternate" or "type II" song. This distinction is common among Vermivorae and other wood warblers. Type I is more frequent early in the season and from unmated males; type II is associated with mated birds and later in summer (though any individual male can sing either song at any time -- these are birds, after all, and they don't read the books). It is also typical for the type II song to be more variable than the type I.

The tonal quality and flat staccato nature of the Bachman's songs is very reminiscent of the type II songs of the Golden-winged and Blue-winged Warblers. A good example of the Blue-wing type II song is here, with a sonogram of one individual song below:

Similarly, here are two examples of Golden-wing's alternate songs:

The Blue-wing has a bit of harshness and dryness compared to the Bachman's and Golden-wing; on the sonogram this is resolved as a visible buzz whereas in the other songs the buzz is too fast to see the individual "ticks" comprising it. This faster, "thinner" quality is also shared by the Golden-wing's well-known "see-bzz-bzz-bzz" primary song as well as the first note of the classic "seeeee-b-z-z-z-z-z-z" type I song of the Blue-wing. This is probably a pretty good guide to what a real, live Bachman's might sound like in person.

In general, the Northern Parula has a less buzzy, less staccato, more tonal quality to its songs. Below is a typical primary song:

When fully executed, this song should provide no confusion with a Bachman's Warbler or anything else. The most common alternate songs also provide little trouble, having a more complex and variable intro but still having the distinctive Parula quality and final note. One variant I have come across that can get your heart pumping, however, is essentially just the staccato, even-pitched intro to the type I song shown above, without the rising segment or the final flourish. This give you just a flat, staccato series of buzzy notes, on first impression rather similar to the second example of Bachman's Warbler (the presumed type II song). On further listening, however, the Parula-like quality has been apparent. If you look at the sonogram, you will see that the individual notes of the Parula trill are "shaped," whereas the Bachman's buzzes are structureless flat boxes. To the ear this is what gives the Parula notes more "musicality," "pitch," or "color."

Now, though, I toss in the monkey wrench. There's a fascinating recording of a Northern Parula responding to a playback of a Bachman's Warbler song, from the site of a former Bachman's nesting area in South Carolina:

This song is eerily similar to the first (presumed type I) Bachman's song; the bird was seen by the recordist so there is no doubt about its identity as a Parula. It appears as though the Parula was actually imitating the Bachman's playback. On close inspection, spectographic differences are noticeable -- the Parula notes have a visible "buzz" to them, and they are less flat in pitch, wavering up and down the scale a bit in typical Parula fashion. These characters can all be picked up by the ear as well on close listening, but there's still a very important lesson in this: An audio encounter alone will never confirm the presence of a Bachman's Warbler, even if it is documented with a recording. Still, if by lucky chance V. bachmanii is not extinct, an audio encounter with a singing male (that leads to visual contact and photographic proof) is still the best bet of finding them, and increased birder awareness of the species' vocalizations (and life history) is the best way to help this unlikely but very happy event come to pass.

As for calls other than the song, no recordings exist and the written descriptions are rather non-distinctive within the pantheon of warbler calls.

Finally, the issue of visual ID. An adult male Bachman's well seen is distinctive; the field marks are covered in those field guides that include the phantom species. In short they are black bib, gray crown with yellow forecrown, no wingbars, etc. Still, you should keep in mind that if you catch a glimpse of a small warbler singing a strange buzzy Vermivora song with yellow underparts and a black throat, it is much more likely to be a Lawrence's Warbler (Blue-wing X Golden-wing hybrid) than a Bachman's. It's probably also more likely to be a Golden-wing X Tennessee or some other weird hybrid than a real Bachman's. A good look is mandatory to see all the diagnostic features, not just a few of them; for a territorial male it should also be attainable. The females are a real challenge; the long-accepted "last photo" of the species has just been reanalyzed and found to be in reality a Yellow Warbler of the "golden" race. The same is probably true of a video circulated a few years ago of a "possible female Bachman's" in Cuba. It might not be possible to prove a female Bachman's at this point without having the bird in hand, given how much more likely any possible bird is to be an aberrant individual of some other species, or a strange hybrid between two common species. At least now for the bird in hand you would just need to retain a few feathers or a drop of blood for DNA analysis and send her on her way, rather than putting her in a museum drawer.

In summary, the basics to keep in mind to put Bachman's Warbler "back on your birding radar:"

1. Biome -- bottomlands anywhere from Missouri to Louisiana and east to the Atlantic; also migrants in peninsular Florida. Forget the "historical hotspots;" their habitat is unlikely to still be suitable.

2. Habitat -- canopy gaps, edges, clearings, openings, areas thinned by storms, etc. that have grown a thick brushy, brambly, and/or caney understory. Think blackberries, cane, and very thick

3. Voice -- the thin dry staccatto of the brushy-buzzy Vermivora complex; typically thinner and weaker than a Parula.

Of course, also remember than even if you are in perfect habitat and hear a dead-ringer song, it's still FAR more likely that you have found a funny Parula or an out-of-range Blue-wing or Golden-wing. Fortunately the other two of the buzzy brushy trinity are usually much easier than large phantom woodpeckers to actually SEE and relocate after you hear one; the same would likely be true for a Bachman's Warbler as well.


At 5:25 PM, Blogger jacob said...

Thank you so much for writing this. I am doing searches in Northern VA do this information will be very useful.

At 12:53 PM, Blogger emupilot said...

I remember reading that sometimes significant quantities of Bachman's Warblers were found in migration in the Florida Keys. Wouldn't that be a good way to look for them at greater density than on their breeding grounds?

At 3:02 PM, Blogger Bill Pulliam said...

Records from Florida were in the 19th Century, from the Keys and from the Suwannee River in the northern peninsula. We know for certain the species persisted on its breeding grounds at least until the 1950s, but there were not more records of migrants in Florida during these many years. The wintering grounds in Cuba are likely a one- or two-hop flight from the breeding range, which would make it very easy to skip over Florida if weather does not force them down. The biggest count for the Keys (21 dead birds at a light tower) were storm-grounded migrants (and in the 19th Century). Whatever the reason, migrants were not found in Florida during many years when the species was definitely extant, so it does not actually seem like a particularly good way to find them.

The Keys are already a heavily birded area and have been for many decades. There's no need to promote increased effort or awareness there.

At 7:51 AM, Blogger Spookpadda said...

The last confirmed sighting seems to be in dispute. When was it?


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