Browsed by
Category: Behavior

Do Bushtits Sing?

Do Bushtits Sing?

(Guest post by Ted Floyd, editor of Birding magazine and bird sound enthusiast)

Fish swim, snakes slither, songbirds sing. Okay, some songbirds’ songs aren’t especially songful: The “song” of the Cactus Wren sounds like an old car starting up, for example, and the “song” of the Yellow-headed Blackbird sounds like someone being strangulated. Nevertheless, the chugging of the wren and the tormented gasping of the blackbird qualify as song, pretty much any ornithologist will tell you.

But some songbirds actually are believed not to sing. Probably the best known example in the U.S. is the Cedar Waxwing. Oh, they’re plenty noisy, flocks of them trilling and lisping and wheezing their way from tree to tree. But they don’t actually sing, it is said. I can see why. I mean, they’re so over-the-top gorgeous, with their waxy wingtips, wispy crests, and just general, well, gorgeousness. One look at a Cedar Waxwing, and it’s love at first sight—whether you’re a human or a waxwing. No need for song.

Less well known is that Bushtits are said not to sing. Like waxwings, Bushtits roam about in noisy flocks. But they’re drab, they’re tiny, they’re not as widespread in the U.S. as Cedar Waxwings, and much of their range comprises hot, arid, rocky, low-diversity shrublands eschewed by many birders. Out of sight (and out of earshot), out of mind.

 —–

Of late, I’ve had occasion to question the conventional wisdom that Bushtits do not sing. Here’s the deal: In just the past couple years, Bushtits have invaded my suburban neighborhood near Denver, Colorado. Suddenly, Bushtits are everywhere. There’s a certain novelty for me about seeing and hearing Bushtits. I find myself paying special attention to Bushtits.

In particular, I’ve noticed that one Bushtit vocalization—a short, high-pitched trill—tends to be given by solitary birds or by birds in pairs. Yes, this vocalization can be heard from birds in large flocks and at any time of the year; in the same way, the Red-winged Blackbird’s classic song may be heard in huge roosts on the wintering grounds. I can see from my field notes, as well as from my comments posted to Xeno-Canto, that I’ve been wondering for a while if this short, high-pitched trill functions as the song of the supposedly songless Bushtit. And I had an experience the other day that really got me thinking.

 —–

Friday, March 6, 2015, was the first sort-of warm day we’d had around here in a while. Even through my closed window, I could hear House Finches singing their twangy warbles and collared-doves chanting “eighteen” in Greek. (Every wondered why they’re called decaocto?) I could also hear the trilling of a Bushtit, so I went outside to investigate. A Bushtit was teed up on a branch in my yard, vocalizing away. I went back into the house, got my recorder, and came back outside again. The bird was still at the same perch and still vocalizing, and I recorded it. Then I did something absurd.

The male Bushtit apparently singing, Boulder County, CO, 3/6/2015. Photo by Ted Floyd
The male Bushtit apparently singing, Boulder County, CO, 3/6/2015. Photo by Ted Floyd

I went back inside, looked for my scope, and looked for my cell phone. I found them, gathered them up, and went back outside. The Bushtit was still there, still vocalizing. I set up the scope, fired up the phone, fiddled with various settings, and got a bunch of photos. That’s absurd! Bushtits aren’t supposed to stay put for ten minutes, as this bird did. They’re not supposed to stay put for ten milliseconds.

But this guy (confirmed as a male by the digiscoped images) was at his perch, teed up, constantly giving the same vocalization. And when I reviewed the soundfiles, I saw something I hadn’t consciously noted while with the bird in real life: Another Bushtit, quite some distance away, was counter-vocalizing with the bird in my yard.

So we’ve got a bird perched for ten-plus minutes, delivering the same vocalization over and over again; the bird’s a male; it’s a sunny and sort-of warm morning in early spring; and another bird is dueting with it. If these were cardinals or chickadees, we’d unquestioningly say they were singing.

But were the Bushtits “really” singing?

The literature says Bushtits don’t sing. I checked Sarah A. Sloane’s BNA account [subscription required], which states: “There is no song in the usual sense. The closest Bushtits get to a song is the somewhat musical, but apparently unstructured, ‘twitterings’ given by many individuals simultaneously when in a close group.” The sprawling account by Arthur Cleveland Bent doesn’t treat song, best I can tell. And a detailed 1903 treatise by Joseph Grinnell likewise contains no mention of song.

Were the Bushtits “really” singing? I think we need first to address another question: What is birdsong? Immediately, I’m reminded of the famous quip by U.S. Supreme Court justice Potter Stewart: “I know it when I see it.” (Or, in the case of birdsong, hear it.) That’s good enough for jurisprudence perhaps, but inadequate for biology. David A. Spector took up the matter in a 1994 paper in the Journal of Theoretical Biology: “Definition in Biology: The Case of ‘Bird Song.’ ” The problem is that different authorities have different definitions, many of them intrinsically circular.

 —–

I’m a scientist by training, but more a philosopher by temperament. I get it, at a scientific level, that the matter of song in the Bushtit is unresolved. It remains to be proved that the male Bushtit’s short, high trill functions as song. I’ve stated a hypothesis; now someone needs to go out and test it.

But I’m temperamentally a philosopher, I said, and I can’t resist ending on that note. The morning after my encounter with the provisionally singing Bushtits, I came upon a Black-capped Chickadee up on a branch. The bird was vocalizing. So was another chickadee, farther away. I made a quick-and-dirty recording; you can clearly hear one bird and sort of hear the other bird, and they’re inarguably singing—singing one of the best known and most beloved songs of any bird in the U.S.

Weren’t the Bushtits doing the same thing?

A Bicknell’s Thrush Critique

A Bicknell’s Thrush Critique

{We interrupt our series on describing bird sounds to bring you this special post.}

In 1995, in the 40th Supplement to their checklist, the American Ornithologists’ Union recognized Bicknell’s Thrush (Catharus bicknelli) as a full species, splitting it from the Gray-cheeked Thrush (Catharus minimus) on the basis of “differences in morphology, vocalizations, habitat preferences, and migration patterns.”  In support of these differences, they cited two papers: Ouellet 1993 and Evans 1994.

The split came under fire earlier this year in an extensive Xeno-Canto forum discussion that focused mostly on the vocal evidence.  Dan Lane gave a rather scathing assessment of Ouellet’s 1993 paper; Andrew Spencer testified that both Bicknell’s and Gray-cheeked respond to playback of one another’s songs, in contradiction of one of Ouellet’s key claims; and I made comments critical of Evans’ 1994 paper, which described differences in the nocturnal flight calls.

Recently, the conversation was joined by Bill Evans himself, the author of the 1994 paper.  In case you don’t know, Bill Evans is one of the great bird investigators of our age — one of the prime movers behind the last few decades’ resurgence in the study of nocturnal migration.   In his Xeno-Canto comment, Bill presented a detailed defense of his paper.  I promised to respond when I got a chance.

I have great respect for Bill Evans and what he’s taught all of us about birds and their sounds, but I’d like to reassess the evidence and arguments in his 1994 paper.  In my opinion, that paper simply did not present strong evidence for a consistent difference in flight calls between Bicknell’s and Gray-cheeked Thrushes.  And yet many have cited it as though it did, not least the AOU when it split the two species.  I’d like to get people thinking about this paper more critically.  Hence this blog post.

Evans’ original case

You can read Evans’ paper online for yourself, but I’ll summarize it here in a nutshell.

  1. Bill Evans collected a number of recordings of nocturnal flight calls of apparent Bicknell’s/Gray-cheeked Thrushes, from Minnesota, Alabama, west-central New York state, and Florida.
  2. He noticed that the Florida calls tended to have a much earlier peak and a higher maximum frequency than the calls from the other three locations (with little to no overlap, according to his table).  In other words, he detected two discrete types of “Gray-cheeked-like” flight calls.
  3. He argued that Bicknell’s Thrush would be expected to migrate directly through Florida, but that only “regular” Gray-cheeks were likely in the other three locations.
  4. He found a daytime recording of a Bicknell’s from Mount Mansfield in Vermont that was a close match for one of his nocturnal Florida calls, and a daytime recording of a Gray-cheeked from Manitoba that closely matched one of his nocturnal calls from outside Florida.  Here’s the figure he used to illustrate this point:

And by virtue of the evidence above, he argued that the nocturnal flight call of Bicknell’s Thrush differs consistently from that of Gray-cheeked Thrush.

When I first read this paper, I found it reasonably convincing, mostly because of Figure 1.  The top-to-bottom similarities and left-to-right differences are obvious, and they tell a clear story.  It’s an excellent piece of visual rhetoric (and I say that admiringly, as a teacher of scientific writing and rhetoric).

But as I started to research the vocal repertoires of Bicknell’s and Gray-cheeked Thrushes for my field guide project, I realized that Figure 1 is far too simple, far too neat. The daytime calls of Gray-cheeked and Bicknell’s Thrushes are extremely variable. So variable, in fact, that if you pick the right recordings, you can construct an alternate version of Figure 1 from Evans 1994, with the two species switched:

Bill said both in his 1994 paper and again in his Xeno-Canto comment that he couldn’t find any Gray-cheeked daytime calls that matched his purported nocturnal Bicknell’s, and he couldn’t find any Bicknell’s daytime calls that matched his purported nocturnal Gray-cheekeds.  Well, these look pretty darn close to me.  The Gray-cheeked call at lower left is a pretty good match for the early-peaked shape of the purported Bicknell’s at upper left, and it’s got almost exactly the same peak frequency.  It’s from the exact same Churchill, Manitoba recording as the one Evans used to create the daytime Gray-cheeked spectrogram “D” (the high, early-peaked call occurs at 1:20, while the “D” call is either the one at 1:26 or the one at 1:36).

Meanwhile, the call at lower right is from one of Andrew Spencer’s recordings of Bicknell’s Thrush from New Hampshire.  Note the “buffalo-humped” shape and the peak frequency all the way down at 4 kHz.

So both species can give high-frequency, early-peaked calls during the day.  And both species can give low-frequency, late-peaked calls during the day.  So why couldn’t they both give both types of calls at night?

The migration-route argument

Evans 1994 argues that Bicknell’s would be expected to migrate through Florida at the time of his recordings, but never discusses whether Gray-cheeked Thrush might also pass through at that time.  But Gray-cheeked appears to be more common than Bicknell’s as a migrant in Florida.  A 2005 paper by Glen Woolfenden and Jon Greenlaw found that of 54 Florida specimens, 47 were Gray-cheeked Thrush, and only 4 were Bicknell’s (with 3 remaining unidentified). Eleven of the Gray-cheeked specimens were from eastern coastal counties, and Woolfenden and Greenlaw could find no differences in migration dates.  A similar situation seems to exist in other southeastern states: Lee (1995) re-examined 24 specimens taken in North Carolina and found that 23 were Gray-cheeked and only 1 was Bicknell’s.

The sheer number of Gray-cheeked specimens from Florida (even eastern Florida in May) suggests that the peninsula is a regular migration route for at least part of the population.  And the ratio of southeastern US specimens suggests that in migration, Gray-cheeks outnumber Bicknell’s throughout the region.  Gray-cheeked winters in northern South America from Columbia east to Guyana — largely south and east of Bicknell’s wintering range on Hispaniola — and Gray-cheeked is reportedly a “trans-Gulf migrant” (according to BNA, etc.).  All of this suggests to me that any given Gray-cheeked-or-Bicknell’s flight call recorded in Florida is more likely to be from a Gray-cheeked.

Evans 1994 reports only high-pitched, early-peaking flight calls from Florida, but Bill’s Xeno-Canto comment indicates that subsequent sampling there has turned up low-pitched, late-peaking flight calls as well.  He wrote, “you don’t get a regular stream of “buffalo humped” GCTH calls in the mid-eastern Florida coast in May unless you have a sustained period (typically 2 days or more) of westerly winds. And there is nowhere else I’ve found in eastern US where one can record a pure set of the higher pitched, steadily descending GCTH calls like those I’ve recorded from eastern FL in May.”

This is an interesting claim.  I’d expect Gray-cheeked Thrushes breeding in Quebec and Newfoundland to pass through Florida even when winds weren’t westerly.  The situation Bill describes is consistent with a scenario in which the high-pitched, early-peaking flight calls are given by eastern Gray-cheeks, while the low-pitched, late-peaking flight call is the hallmark of the western Gray-cheek, with Bicknell’s either unrepresented in the sample, or overlapping eastern Gray-cheeks. At the very least, I don’t know how Bill can rule such a scenario out.

Also, the phrases “a regular stream” and “a pure set” ring my alarm bells.  They suggest that “irregular streams” and “impure sets” — such as the odd “Gray-cheeked-type” call on a non-westerly Florida wind, or the odd “Bicknell’s-type” call outside the range of Bicknell’s — might be dismissed as “atypical,” resulting in unwitting confirmation bias.  (More on the dangers of the word “atypical” here.)

Daytime call variation

I’ve put together two animated spectrogram GIFs to show how the daytime calls vary in individual Gray-cheeked and Bicknell’s Thrushes.  They both loop at 10 frames per second.

65 consecutive calls from an individual Gray-cheeked Thrush, Nome, Alaska, 6/1/2007. Recording by Gerrit Vyn. Click to listen to original (Macaulay Library catalog #137552).

67 mostly-consecutive calls from an individual Bicknell’s Thrush, Jefferson Notch, NH, 6/24/2008. Recording by Andrew Spencer. Click to hear original (split into 4 Xeno-Canto files).

Both GIFs are at exactly the same scale: the top of the graph is 6 kHz. Notice how peak frequency changes, as well as call shape.  No call forms are exactly shared, but some are strikingly similar.

Notice, too, that the calls don’t vary at random.  Birds of both species repeat the same call many times in a row. Then they either switch immediately to a different call type, or transition into the new type via 2-3 intermediate calls.  The Gray-cheeked uses four different call types in this sample; the Bicknell’s uses five.  If we had longer recordings, it’s likely we’d hear more call types from each individual: recordings and various published reports put individual call repertoires at up to 10 in both species (e.g., Ball 2000).  And repertoires of neighboring birds tend to be similar, as evidenced by recordings and reports of call matching by neighboring birds.  But across the geographic range, these calls vary greatly; Marshall (2001) found a huge variety of call forms across the continent.

These locally-similar but regionally-different repertoires of call notes vary in a pattern like that seen in Red-winged Blackbirds and Lapland Longspurs, and the pattern strongly suggests that the burry daytime calls of Gray-cheeked and Bicknell’s Thrushes are learned, not innate.  If the calls are learned, then regional differences would be expected to arise over time, in exactly the same manner as song dialects.  Some call types might be heard less often in one population and more often in another; some might become exclusive to a particular area.  Gray-cheekeds breeding in, say, Quebec or Newfoundland (and migrating through Florida) might use higher-pitched, earlier-peaking calls with greater frequency than Gray-cheekeds breeding farther west.

And this raises several questions.  If each individual thrush knows 5-10 different daytime versions of its burry calls, which one (or ones) does it give during nocturnal migration?  Or is the night flight call completely separate from the daytime calls?  Is it innate or learned?  Do individual birds have repertoires of night flight calls, or is there just one per bird?  When we see variation in nocturnal calls, how much of it is individual, how much of it is dialectal (that is, geographic), how much of it is repertoireal (I just made up that word), and how much of it is due to mere plasticity?

These questions matter, and right now we don’t know the answer to any of them.  Even if we know the answers to these questions for other species, it may not be safe to assume that Gray-cheeked and Bicknell’s are the same.  After all, among North American Catharus thrushes, only Veery shares their trait of having not just one daytime flight-call-like sound per individual, but a repertoire of such calls.

Conclusion

Based on all the research I’ve done, I have a hunch that during the day, Bicknell’s is indeed more likely on average to give the higher-pitched, early-peaking calls, while Gray-cheeked is indeed more likely to give the lower-pitched, later-peaking calls.  But the overlap seems pretty much complete, and I suspect that few, if any, nocturnal call forms are diagnostic for one species or the other.  Remember, in bird identification, it’s not enough to find a match; you have to rule out other potential matches.  If Gray-cheeks are capable of making the Florida-type calls, then how do we know they didn’t?  How do we know the higher-pitched, early-peaking calls aren’t more common in eastern populations of Gray-cheeked?  How do we know that the existence of two call forms in Florida isn’t an artefact of limited sampling?

I’m perfectly willing to believe that Bicknell’s and Gray-cheeked Thrushes do differ in nocturnal flight calls.  I’m even willing to believe there’s little overlap.  But if I’m going to believe it, I need some evidence more solid than anything I’ve seen yet.

Long Calls of Gulls

Long Calls of Gulls

Herring Gull in “oblique” posture at end of long call, Acadia National Park, Maine, 8/3/2008. Photo by Dick Daniels (CC 3.0)

A couple weeks ago, I was puzzling over a group of distant gulls on a reservoir in Wyoming.  I was fairly sure they were all the same species, but through my binoculars, I couldn’t quite decide whether I was looking at Ring-billed or California Gulls.  Then, from across the water, I heard one of them give a hoarse, slow “koo-WEEE? kweee? kweee? … QUIRK! …  QUIRK!” and I confidently checked the “Ring-billed” box in my checklist app.

As I wrote last year, most people don’t listen to gulls much.  But as I’ve paid more attention to them over the past year, I’ve realized that many species can indeed be identified by sound alone, and this fact has greatly improved my birding skills.  In today’s post I’m hoping to provide a basic framework for beginning to identify some of the species by sound.

What’s a “long call”?

The “long call” is the most complex vocalization in a gull’s repertoire, and one of the most frequently given. “Long calls” can be heard year-round in a variety of situations, but they most often serve as aggressive signals directed at other gulls.  They vary within individuals based on excitement level, but individuals may be able to recognize each other by long call.  The long calls of different species tend to sound rather different.

You can think of the archetypal “long call” as containing three parts:

Ring-billed Gull long call, Washington County, Colorado, 9/7/2009
  1. The intro notes are highly variable depending on the bird’s level of excitement, and are often totally absent.  When present, they usually take the form of short barks, as in the example above; long mewing wails; or a mix of the two.
  2. The squeals are the start of the long call proper.  They are by far the loudest, and usually the longest and highest-pitched, notes in the call, and they usually coincide with a distinctive motion of the head, such as a deep bow and/or a backward head toss.  There are usually only 1-2 squeals, but occasionally three or even more if a bird is excited.  (Some species don’t really “squeal” at this point in the call, but I couldn’t think of another good name for these notes.)
  3. The terminal series is the series of similar notes that ends the call.  The  number of notes varies with excitement level, but the sound and speed of the notes tend to be fairly consistent within species, making this generally the most useful part of the call in identification.  Most species adopt an “oblique” posture for the duration of the terminal series (see Herring Gull photo above), but some, like Ring-billed Gull, give distinctive motions of the head with each note.

Most large North American gulls sort out pretty well into groups that follow similar patterns in their long calls.

  • High yelpers, usually clear: Herring, Glaucous, Western, Glaucous-winged
  • Low yelpers, often hoarse: California, Lesser Black-backed, Great Black-backed
  • Slow squealers: Ring-billed and Mew
  • Nasal: Heermann’s, Franklin’s, Laughing

The High Yelpers

These are the “classic seagull” sounds as brought to you by Hollywood.  In this group, the terminal series usually consists of clear (not hoarse) high-pitched yelps, often without much change in pitch or speed. Western and Glaucous-winged average lower in pitch than the other two species, and tend to have simpler calls, very often omitting the intro notes and squeals.  Glaucous and Glaucous-winged average slower than Herring and Western, with fewer notes per call.  However, individual variation often makes it difficult to tell these four species apart by vocals alone.

The Low Yelpers

This group resembles the first group, except that the pitch of the terminal series averages lower and more nasal (almost more “bugling” than “yelping”), and there is a much greater tendency towards hoarse or harsh tone qualities.  Great Black-backed tends to be the lowest of these.

The Slow Squealers

Ring-billed Gull long call, Adams County, Colorado, 1/24/2013

Mew Gull long call, Alaska, 6/28/2006. ML catalog #132251
http://earbirding.com/blog/wp-content/uploads/2013/08/Ring-billedGull_04_longcall_RBGUlongcall2_SPlatteAdamsCO_NDP2013-01-14_ii.mp3 Click here to listen

These two closely related species have a distinctively slow delivery — typically about two notes per second in the terminal series.  The pitch tends to be high and the quality rather squealing.  Tone quality separates them: Ring-billed’s voice is distinctively scratchy or screechy, especially in the terminal series, while Mew tends to have a much clearer tone.  In Ring-billed, at least, each note in the terminal series is usually accompanied by a distinctive vertical pumping of the neck with the bill held skyward, as though the bird were jabbing its bill at an airborne opponent with each cry.

The Nasal Gulls

Laughing and Franklin’s Gulls were recently moved from the genus Larus into the genus Leucophaeus, reflecting our understanding that they are not closely related to the other gulls on this page.  Their immediately distinctive voices, high-pitched and nasal, are evidence of this evolutionary distance.  Their long calls are also unique in structure, lacking the “intro>squeal>series” pattern of other gulls.  Laughing Gull is the only gull that consistently starts with a fast series of notes followed by a slow series of notes. Franklin’s, meanwhile, usually gives a simple slow series of rising notes at one speed.  The fast notes of Franklin’s, if they occur at all, usually come at the end.

Then there’s Heermann’s Gull.  There’s no mistaking it for any other West Coast species.  Imagine the long call of a Herring Gull, as performed by a Red-breasted Nuthatch:

There’s a lot more to gull vocalizations, but hopefully this post can get people started on what to listen for.  I still have a lot to learn about identifying these birds by sound, and I’d be glad to get your insights in the comments.

Empid Mystery Solved!

Empid Mystery Solved!

Remember the mysterious two-part call of the unidentified Empid?  Nacho Areta left a comment this morning on my last post about the sound, pointing out a third example of the mystery sound in the Macaulay Library — this one attributed to Least Flycatcher.  That’s right, the three different recordings of this sound have been identified as three different species — Yellow-bellied, Alder, and Least!

“Whit-beert” call, labeled as Yellow-bellied Flycatcher.
Woodhull Lake, New York, 5/30/1998. ML catalog #106901		 “Whit-beert” call, labeled as Alder Flycatcher.
Upton, Maine, 6/2/1962. ML catalog #7546		 “Whit-beert” call, labeled as Least Flycatcher. Brown Tract Lake, New York, 5/28/1999. ML catalog #100852

Nacho asked why the calling bird in all three cases couldn’t be Least Flycatcher.  As I went back to review my notes on that species, I realized he’d solved the mystery.  I’d already picked out several examples of what I had tentatively named the “pweet series” of Least Flycatcher, and ML 100852 was one of them — I had simply failed to recognize the resemblance to the mystery call.  Once I went looking for it in the Least Flycatcher collection, I found more examples:

   
Least Flycatcher. Brown Tract Ponds, New York, 5/30/1999. ML catalog #100876 Least Flycatcher. Bruce Peninsula, Ontario, 5/21/1993. ML catalog #63954

And that last recording is the true Rosetta Stone, because not only does it feature the mystery call, but also many nice unambiguous renditions of the species’ song: the snappy, repeated “che-BEK” that clinches the ID of Least Flycatcher.

Nacho points out that this vocalization type doesn’t have to be a 2- or 3-noted pattern; it’s frequently a longer series.  That, plus the somewhat variable nature of the initial “whit” call, partially explains why these Least Flycatcher recordings were able to sneak right past me, even as I looked directly at the spectrograms.  The entire affair highlights the tremendous usefulness of collaboration in solving mysteries like these!  Thanks to Nacho Areta and everybody else who helped out with comments.

More on the Mystery Empid Call

More on the Mystery Empid Call

A few months ago I wrote about a mysterious new “whit-beert” call that I had discovered in the bowels of the Macaulay Library’s online collection, and which I took to be a previously undescribed sound of Yellow-bellied Flycatcher.  Noticing a certain resemblance to the “dew-hic” call of Dusky Flycatcher and the “peer-pewit” call of Hammond’s Flycatcher, I concluded that the new call was likely homologous with those sounds — that is, that the “dew-hic,” the “peer-pewit”, and the “whit-beert” are all evolutionarily derived from a similar call given by the species’ common ancestor.

Now, new information has come to light that calls my earlier conclusions into question.  First of all, Empid guru Arch McCallum told me he wasn’t convinced that the “whit-beert” was equivalent to “dew-hic” and “peer-pewit”, due to the different spectrographic shape of the “whit” and the fact that it was never repeated.  Instead, he pointed out the similarity of “whit-beert” to certain calls of Willow and Alder Flycatchers.

He may have hit the nail on the head.  I recently discovered a second recording of the mysterious “whit-beert,” from western Maine, labeled as an Alder Flycatcher.

“Whit-beert” call, labeled as Yellow-bellied Flycatcher.
Woodhull Lake, New York, 5/30/1998. ML catalog #106901		 “Whit-beert” call, labeled as Alder Flycatcher.
Upton, Maine, 6/2/1962. ML catalog #7546

The new recording was taken in 1962, before “Traill’s” Flycatcher was split into Willow and Alder. The recordist was Dr. Robert C. Stein, who had already realized that “Traill’s” sorted into two vocal groups, and was in the process of collecting data for his classic 1963 publication that provided the first strong evidence for the eventual species split.  The notes on the recording indicate that the recording was made during a “hostile response to playback,” but it doesn’t say what sound was used for playback, nor does it explain how the recording was identified as an Alder Flycatcher.

So: which species is it that gives the “whit-beert” call?  Personally, I agree with Arch that Yellow-bellied is probably the least likely culprit.  Alder is the leading contender at the moment, followed by Willow.  But to answer the question definitively, I think we’ll need some more recordings.

If you’re interested in helping to solve the mystery, you might try some playback experiments in northeastern North America this spring.  Does playing “whit-beerts” to an Empid elicit more “whit-beerts”?  What species says “whit-beert,” and what is the behavioral context of the sound?

I don’t think anybody knows the answer to the questions I just asked.  I don’t think anybody has ever known.  But they could be easily answered by anyone with an audio recorder and a couple of spare hours in New England this summer.

This is what I love most about bird sounds — the tantalizingly short distance to the frontier of knowledge.

The “Tink” Call

The “Tink” Call

Bay-breasted Warbler, Rondeau Provincial Park, Ontario, 5/5/2007. Photo by Mdf (CC 3.0).

Not too long ago, it was commonplace for birders to make casual references to THE call or THE song of a bird species, as though every bird had only two modes of communication.  Now we know better.

These days, I’m more likely to hear casual references to THE flight call and THE alarm call.  After all, when we notice that, for example, many species of warblers and sparrows give similar high “seets” on the wing in migration and sharp “chips” in alarm when perched, it makes sense to group those calls into categories and name them after similarities in their form or function.

But there’s an odd, insidious trick of psychology at work in all of us.  If a sound doesn’t match our expectations — if it doesn’t fit one of our pre-existing mental categories — we’re much less likely to hear it.  If we do hear it, we’re likely to dismiss it as a quirk of the individual, a bird doing “something weird.”  Or else we’ll just cram it into a category we recognize: “must be the flight call, I guess.”

Something like this happened to me as I researched the “call notes” of various warblers.  I regularly ran into sounds that didn’t fit my mental categories, and after a brief period of confusion, I tended to dismiss them as atypical versions of the normal call.  Beware that word “atypical” — it strongly suggests that what you’re hearing is best ignored, that it’s an outlier at risk of messing up your dataset.

A few months ago, an online chat with my co-blogger Andrew Spencer started unraveling some of my preconceptions:

Andrew: are you going to cover alarm calls in warblers?

me: What kinds of alarm calls?

Andrew: those high pitched tink calls that many warblers give

like http://www.xeno-canto.org/13861

I think every warbler just about does tink calls when alarmed

I heard Connecticut Warbler give one

and I’ve heard it from a number of other species

but I don’t know how many recordings there are

me: Just higher-pitched versions of the normal call? Or something distinct?

Andrew: the one I linked of the Orange-crowned Warbler is distinct I think

all the ones I’ve heard sound damn near the same

me: I remember when I was researching Louisiana Waterthrush calls I came upon a recording in the Macaulay collection of a bird giving calls much higher than all the other recordings — more like your tinks. I just figured it was a crazy variation on the normal call.

Andrew: I have calls like that from Black-throated Blue Warbler as well: http://www.xeno-canto.org/30783

me: And I have a recording of an agitated Kentucky Warbler switching back and forth from a chip-like to a tink-like note.

Andrew: and I got a few from Golden-winged Warbler this past trip

me: These “tink” notes appear to be poorly described in field guides and the literature.

Andrew: doesn’t surprise me

me: This calls for a blog post.

Andrew: haha I was about to say the same thing

As soon as I started digging, I realized that these “tink” calls hadn’t gone unnoticed by everyone.  Paul Driver featured them on his blog back in 2009, under the name “high chip calls”:

A number of warblers (perhaps most?) have high chip alarm calls different to the typical chip call, sounding more like titmice or Golden-crowned Kinglet. They seem to be heard most often on breeding grounds and are often given by birds that are highly agitated; in this way they seem analogous to the high chip call of the Song Sparrow.

Funny he should mention Song Sparrow.  Recordings show that a great many species of sparrow give a “tink” note that sounds much like the “tinks” of warblers, and is given in similar situations of high alarm.  (This warbler-sparrow similarity is no coincidence – but that’s a subject for another day.)

These “tink” notes seem worth of their own category, separate from the “call” and the “flight call.”  They tend to indicate a higher level of alarm than “typical” calls, but not as high as the buzzes and shrieks that these birds give when they’re really upset (e.g., when a predator is attacking a nest, or when the bird is caught in a mist net).  Sometimes one hears calls intermediate between the high “tinks” and the lower “chips,” especially from sparrows.

“Tinks” can raise some interesting questions.  In some species, like Cape May Warbler, the “typical” call sounds much like a tink, and there may be little distinction — or is it perhaps that the tink is just more frequently given, so that we think of it as typical?  At the very least, if you happen to be in the habit of identifying Cape May Warblers by call alone, the existence of similar sounds in all these other species should give you pause.

An online catalog of “tink” recordings

Not every warbler and sparrow has a “tink,” apparently. For example, I haven’t been able to find any convincing examples from the genus Spizella (except for American Tree Sparrow, which many researchers agree is misplaced in Spizella and overdue for a move to its own genus).

I’ve attempted to assemble a collection of “tink” recordings that are available online, in order to document their existence in as many species as possible.  No doubt there are other “tinking” species not currently represented below.

If you can add to the list above, or have other useful observations of “tink”-like notes, let me know!

Learning Laplands

Learning Laplands

Lapland Longspur, Kodiak National Wildlife Refuge, Alaska. USFWS image in the pubic domain.

In wintertime, huge numbers of Lapland Longspurs come down to the northern United States from their Arctic breeding grounds — sometimes gathering in enormous single-species flocks, but often mixing with other longspurs, Horned Larks, and Snow Buntings. At a distance, their cryptic winter plumage pattern can make them hard to pick out from these other birds. That’s why many people “look” for longspurs with their ears.

Away from the Great Plains, Lapland is usually the only expected longspur species, and one can usually detect and identify it by its characteristic rattle call, which generally resembles the rattles of other longspurs.  Although the number of notes is highly variable, this call is pretty much the same across the Lapland Longspur’s entire (worldwide) range:

Lapland Longspur rattle, Weld County, CO, 11/19/2007.

But this isn’t all that longspurs say.  They give a variety of other calls, some of which are more immediately distinctive than the rattle.  Here in Colorado, I recorded a longspur giving “chewlup” and “terlee” calls in addition to rattles:

As I started listening to recordings of Lapland Longspurs from other parts of North America, I started to hear other types of calls.  Individual birds give at least 5 or 6 different whistled calls, especially on the breeding grounds, and individual repertoires seem to differ, especially from one geographic region to the next.  In trying to catalog Lapland Longspur calls, I ended up making a map of variation.  First, I found recordings from seven distinct locations where this species breeds in the North American Arctic:

  1. Seward Peninsula, western Alaska (LNS 49598 and LNS 141100)
  2. Denali National Park, central Alaska (LNS 50024)
  3. Colville River Delta, northern Alaska (LNS 131257)
  4. Babbage River, northern Yukon (LNS 61441)
  5. Bathurst Island, Nunavut (LNS 137341)
  6. Devon Island, Nunavut (LNS 61444)
  7. Baffin Island, Nunavut (LNS 61426)
Locations of the Lapland Longspur recordings

Then I went through the recordings and made a table showing the geographic similarities and differences in calls:

In the table above, all the spectrograms in a given row represent different calls from the same individual bird (except for the first row — the “chewlup” and “ter-lee” are from a different bird than the other three).  Here are the takeaway lessons:

  1. Some calls are clearly the same across wide portions of the range. For example, the call that sounds like “ti-turtle” is clearly the same in western Alaska, northern Alaska, and the northern Yukon.  But it does not appear in recordings from other regions — at least not in a recognizable form.
  2. This graph isn’t wide enough to show all the types of calls. In particular, the recordings from northern Alaska (#3) and Bathhurst Island (#6) contain multiple call types that I didn’t include because they didn’t seem to fit into any of the existing columns.
  3. Few, if any, of the whistled calls are truly universal. The only whistled call type that comes close to appearing in all regions is the “few,” and even then I’m not certain that the “fews” I illustrate above for Devon and Baffin Islands are really equivalent to the “fews” from elsewhere.  It’s possible that more recordings would change this, but note that the extensive recordings from northern Alaska and Bathurst Island show an almost complete lack of shared calls — and that includes the ones I left out for lack of space.
  4. Most, if not all, of the calls can be heard in winter as well as summer.  Though rather few recordings are available from wintering birds, it appears that the calls of longspurs wintering in western North America and on the Great Plains tend to resemble the those from Alaska (locations 1-3), while the calls of longspurs wintering in eastern North America tend to resemble those from Arctic Canada (locations 5-7).

What can we conclude from this information?  Well, for starters, it’s pretty clear that these calls are learned, not innate.  That would explain why birds from a given region tend to share call types, while birds from far away tend to sound quite different.  It fits a pattern of regional dialects that are typical of learned vocalizations.  Each bird learns not just one call typical of its region, but an entire set of regional calls — much like the Red-winged Blackbirds I discussed a while back.  In longspurs, like in Red-winged Blackbirds, dissimilar calls likely fulfill similar functions in different regions of the Arctic.  For example, longspurs expressing agitation at a human near a nest tend to cycle through 3-4 different call types — but the birds on Bathurst cycle through a totally different set of calls than the birds on the north slope of Alaska.

Obviously, people attempting to identify Lapland Longspurs by their calls in winter have their work cut out for them.  My general impression is that longspurs wintering in Colorado sound the same year after year, consistently giving “few,” “chewlup” and “ter-lee” calls like the northern Alaska birds above.  But if I went to, say, Iowa, the longspurs would be likely to sound rather different.

Much remains to be learned about the Lapland Longspur’s complex communication system.  I’m looking forward to knowing more.

The Visual Power of GIFs

The Visual Power of GIFs

Animated GIF: quintessential genre of the modern internet.  A good proportion of the web is devoted to these short, silent looping video clips, mostly in the service of slapstick humor.  But GIFs have significant educational potential as well, especially when it comes to the visualization of patterns — which is what this whole website is all about.

Visualizing variety

Ornithologists use the term variety to describe the pattern of delivery of a bird song over time.  Some individual birds sing only a single song over and over (no variety).  A bird that can sing multiple songs might choose to sing one for a while before switching (eventual variety), or it might switch constantly (immediate variety).

In the field, it can take many minutes of listening to determine a bird’s pattern.  Animated GIFs of spectrograms can condense all this listening into just a few seconds of looping video:

Olive-sided Flycatcher

Carolina Chickadee

Hermit Thrush
No variety
(all songs
identical)		 Eventual variety
(songtypes repeated several
times before switching)		 Immediate variety
(consecutive songtypes
always different)

In each GIF above, the spectrogram of a single bird song appears on the screen for one fifth of a second. It is then replaced by the spectrogram of the next song by the same bird.  After a couple dozen songs, the animation loops back to the beginning.

Seeing song similarities (and differences)

As all naturalists know, the pieces of nature rarely fit into neat categories — and so it’s no surprise that the three categories of variety above are inadequate for describing the more complex patterns of variation found in many bird songs.  A GIF, though, might be up to the task.

Take these 18 songs from a Vesper Sparrow:

Vesper Sparrow, Montezuma County, CO, 5/11/2008.

Note that the level of variety at the beginning of each song is completely different from the level of variety at the end.  Each song starts with the same 3 (rarely 4) downslurred whistles, followed by the same rapid series of vertical notes (the number varying from 5 to 7).  After that, variety increases dramatically.  The middle section irregularly alternates between two different patterns, and the ending switches even more frequently, between at least three different motifs.

This type of cascading variety is typical of Vesper Sparrows.  The opening notes tend to vary little within an individual, but by the end of the song, variation is tremendous.  Perhaps this allows the sparrows to “have it both ways” — that is, to simultaneously send two conflicting messages to the listener.  The stereotyped opening satisfies their need to identify themselves unambiguously to a potential mate or rival (“I am a typical Vesper Sparrow!”), while the jazzy ending allows them to show off their improvisational virtuosity (“I’m not your ordinary Vesper Sparrow!”).

I’m fascinated by the potential for GIF visualization… perhaps you’ll see more animated spectrograms on this blog in the future.

What’s Weird About Rusty Blackbirds

What’s Weird About Rusty Blackbirds

Rusty Blackbird, Cleveland, Ohio, 10/9/2011. Photo by Laura Gooch (CC-by-nc-sa).

The voice of Rusty Blackbird isn’t particularly well known.  Perhaps because the species is uncommon and its breeding grounds rather remote, it’s never been the subject of a formal bioacoustic study.  But Rusty Blackbirds sing quite a bit — both males and females sing, in fact.  They sing on the breeding grounds, on migration in fall and spring, and pretty much all winter long.  The winter flocks I encountered in the swamps of Arkansas could be heard for half a mile.

Several authors have described Rusty Blackbirds as having two types of songs — one more creaking, one more gurgling — and this would make sense given that the closely related Brewer’s Blackbird has also been reported to have two different songs of more or less the same types.  As I went through online recordings of Rusty Blackbirds, however, I came to the conclusion that I was hearing three different types of songs from the species, not two.  Or is that two types of song and a very song-like call?

Three things Rusty Blackbirds say

The gurgle-creak seems like a good candidate for a typical “song.”  It starts with a complex jumble of rapid notes and ends with a high monotone whistle with a metallic quality, like the creak of a rusty hinge:

Another song-like sound is the gurgle.  It’s like the first part of the gurgle-creak, but at least twice as long.

Then there’s the creak.  It’s like the gurgle-creak, but starts with only 1-2 quick notes, usually including a noisy “chuck” note much like the species’ contact call.  On the spectrogram below, two creaks follow a gurgle-creak:

It’s fairly clear that these three song-like sounds are associated with different behaviors.  The gurgle-creaks seem typical of songs — they’re practiced throughout the winter, getting gradually more stereotyped; they’re heard from spring migrants, who seem to have mastered them by the time they head north; and they’re delivered in long bouts on the breeding grounds, where they apparently function in territorial defense and mate attraction.

The gurgles, unlike the gurgle-creaks, are rarely heard on the breeding grounds.  Instead, they mostly seem to be given by birds immediately prior to or during spring migration.  The only recording I know of from the breeding grounds is from early in the season — 4 June in northwest Alaska.  Perhaps they function primarily in pair establishment, and are used for just a few days after arrival on breeding territories.

Then there are the creaks, which seem to occupy an odd territory in between traditional “calls” and “songs.”  Like traditional “songs,” they appear to be learned rather than innate — birds spend the winter practicing them, and the finished springtime performances vary greatly from one male to the next.  Furthermore, they’re often deployed along with the gurgle-creaks by territorial birds on the breeding grounds, in response to playback of a rival’s song.  That pretty well matches the classic definition of “song.”

But when else do we hear creaks?  When Rusty Blackbirds mob Common Ravens.  And in response to a tape of Northern Goshawk.  And when a human threatens a nest.  Most birds do not give songs, or anything like a song, in these situations.  Instead we’d expect to hear alarm calls — typically harsh, noisy, simple sounds that carry far and don’t change from one bird to the next.  Rusty Blackbirds have such calls — sharp chucks, long churrs, rattling chatters, and the like.  As one would expect, they readily chuck and churr and chatter at ravens and goshawks and people, but they also give song-like creaks.  What’s up with that?

Longtime readers of this blog will know that I don’t put much stock in the traditional “song/call” distinction, and here’s one more example of why not — a peculiar sound that straddles the traditional boundary in both form and function.  Rusty Blackbird has attracted a fair amount of research attention in recent years due to evidence that its populations may be in steep decline.  But I’m unaware that anyone has attempted to investigate its vocal communication.  Here’s hoping someone will take it on — I think this bird deserves it.

The Dawn Song of Brown Creeper

The Dawn Song of Brown Creeper

Brown Creeper, Pueblo County, CO, November 2006. Photo courtesy of Bill Schmoker

The dawn chorus. You love it or you hate it.

If you hate it, it’s probably because you don’t appreciate being roused from sleep by a vigorous burst of birdsong in the early morning darkness.  This is a common sentiment in the parts of the world where we now think of nature as an interruption of our experience, rather than the medium through which it flows.

If you love the dawn chorus, it may be for its music, its regularity, its symbolism.  Or just for the happy reminder that nature survives, at least in some form, right outside the window.

I love the dawn chorus in part because it contains songs that you can hear at no other time of day.  A number of North American birds sing dawn songs unlike anything they say after sunrise. I’ve written here about several: Violet-green Swallow, American Robin, Cassin’s Kingbird, Cordilleran and Pacific-slope Flycatchers.  But if you had asked me six months ago whether Brown Creeper had a distinctive dawn song, I would have told you no.

Here’s the typical song of the Brown Creeper — a short high-pitched warble, repeated without much variation:

Most sources say that this song can be heard at any time of day.  Some observers have reported hearing it as early as 4:50 in the morning, but it doesn’t seem to be given regularly or repeatedly at that hour.  Instead, most Brown Creepers apparently start their day with utterances like this one:

 

Brown Creeper dawn song, Coos County, OR, 7/1/1990. Recording by Geoff Keller (ML 50337).

(Click here to listen to this recording at the Macaulay Library website.)

Two “tseew” notes followed by two “trill” calls may not sound like much of a dawn song, especially since the “tseew” and the “trill” are two of the common calls given by Brown Creepers throughout the day — the “tseew” mostly in alarm, the “trill” in a variety of situations.  But this is not just a string of calls mixed together at random.  The calls comprise a repeated and stereotyped sequence: “tseew tseew trill trill… tseew tseew trill trill… tseew tseew trill trill… tseew tseew trill trill.”   The exact pattern varies from one bird to the next, but each individual adheres to its own fairly rigid syntax and rhythm.  They’re not just calling, they’re singing.

Brown Creepers, unlike many other species, appear to transition gradually from dawn singing patterns into daytime singing patterns.  They start out with these stereotyped patterns of “tseets” and “trills” and then, as the sun rises, they start tossing in “regular” song strophes more and more frequently.  Here’s a sunrise recording from New Jersey in which the dawn songs and the day songs are alternated.  And here’s a dawn-singing bird from Arizona that introduces each strophe of day song with components of the dawn song:

I have a recording, also from Arizona, of a Brown Creeper doing something similar as late as 9:00 AM.  Later in the day, the dawn song patterns apparently disappear altogether.

More study of Brown Creeper dawn-singing is needed.  For example, it would be interesting to determine patterns of individual and geographic variation, and to find out whether and how birds respond to playback of the dawn song.  If you live near Brown Creepers, it wouldn’t be too difficult to find answers to some of these questions next spring — as long as you’re willing to rise before the birds.