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A Robin’s Many Songs

A Robin’s Many Songs

Anyone who listens thoughtfully to robins can’t help but bubble with questions about why robins are the way they are.
–Donald Kroodsma, The Singing Life of Birds, p. 37

American Robin along the Platte River, Nebraska, 3/22/2010. Photo by Len Blumin (Creative Commons 2.0).

The American Robin may be the most familiar bird in North America, but for all its abundance and approachability, it remains in some ways inscrutable.  Back in 1979, in his classic Stokes Guide to Bird Behavior, Donald Stokes wrote that robin courtship displays remained a mystery, and might not exist at all.  The song he called an “enigma,” pointing out that it did not appear to correlate with courtship or territoriality, instead peaking right before the young hatch in any given brood.

Some studies in the 1990s provided evidence that robin song is indeed correlated with courtship and territoriality, but they did not make any attempt to describe the song comprehensively.  That task fell to Donald Kroodsma in his popular 2005 book The Singing Life of Birds.  Each male robin, Kroodsma explained, has in his repertoire 6-20 simple, whistled “caroling” phrases and 75-100 high-pitched, complex “hisselly” phrases.  The familiar daytime song is often made up purely of caroling phrases:

  • carol carol carol… carol carol carol carol

But at dawn, the male robin often throws a hisselly phrase in at the end of each strophe:

  • carol carol carol hisselly… carol carol carol carol hisselly

In addition, some robins occasionally give long strings of hissellys without any caroling phrases:

  • hisselly hisselly hisselly hisselly hisselly hisselly…

Kroodsma documents all this and more; and yet, after fifteen pages of descriptions, explanations, and explorations, he still finishes with more questions than answers:

“Why have two types of phrases, the caroled and the hisselly phrases?  Why have a dozen or two of the caroled phrases and a hundred or so of the hisselly phrases?  Do other robins count how many a male sings, and if so, is having more songs better in any way?  Why are the hissellys used mainly at dawn and dusk?  Why at dawn are three or four caroled notes followed by a single hisselly, and what could it possibly mean to sing 71 hissellys in a row?”

The average American probably hears more song from robins than from any other bird, and yet we still cannot answer any of Kroodsma’s questions.  Perhaps it is because we do not listen as carefully as we could; and perhaps it is also because what we call “song” in robins is even more complex than Kroodsma’s work has already shown.  Today’s post will push the exploration of robin song a little further, in hopes of facilitating the kind of listening (and recording) that could begin to solve the many mysteries surrounding America’s favorite bird.

Caroling phrases

First, here’s an example of the “caroling phrases,” the familiar short, clear, 1-3 syllabled phrases that we often hear during the day:

American Robin caroling song, Boulder, CO, 4/24/2008.

Hisselly phrases

Kroodsma described the hisselly as “an ethereal whispered note much like the delicate flourish at the end of a Hermit Thrush song”.  The hissellys shown below, all from the same individual male robin, have been edited together for comparison.  Note that they are much higher-pitched and more complex than the caroled phrases, with a great deal more polyphony:

Ten "hisselly" phrases from one American Robin, edited together. Boulder, CO, 5/26/2008.

Whinnies

The “whinny” is a familiar call of the robin, often given when the birds are alarmed:

Typical American Robin whinny call, Larimer County, CO, 6/19/2008.

But it’s not just a call.  At least at certain times, the whinny (or something much like it) becomes an important component of the robin’s song — and each individual male robin knows an awful lot of different whinnies.  Here are six that one male robin incorporated into his song within a two-minute span:

Six different whinnies from the song of a single male American Robin, edited together. Boulder, CO, 5/26/2008.

Note the complex and stereotyped fine structure above.  These are no mere alarm calls; they are song elements, no doubt about it.

Putting it all together

Here’s a confusing recording of a robin singing with carols, hisselys, and whinnies all mixed together — in fact, he is the sole source of all the hissellys and whinnies on the edited tracks above.  I recorded him in late May in Boulder, Colorado, and though there were many other robins in the immediate vicinity, none were interacting with this bird that I could see; he was perched up in a tree just belting out his song.  What in the world can he possibly be saying?

American Robin song, Boulder, CO, 5/26/2008.

The beginning of this bird’s song, illustrated on the spectrogram above, follows a pattern like this:

  • hisselly (or 2-noted whinny?) carol hisselly hisselly hisselly whinny hisselly whinny hisselly whinny hisselly…

I do not know what is going on with this bird, but its song suggests that anyone seeking to understand robin song should think of the whinnies as a type of song phrase on par with the carols and hissellys.  At the same time, it reinforces what you’ve probably already realized: anybody seeking to understand robin song has a lot of work to do.

To Stereotype or Not

To Stereotype or Not

Lilac-crowned Parrot, a species with relatively unstereotyped vocalizations. Arizona-Sonora Desert Museum, Tucson, AZ, 5/13/2009. Photo by DrStarbuck (Creative Commons 2.0).

Lately I’ve been thinking a lot about stereotype. Not the racial or ethnic kind, but the degree to which a bird’s song is the same each time it’s sung. In a couple of recent blog posts, I showed that Violet-green Swallows and Evening Grosbeaks produce stereotyped vocalizations in complex strings, and therefore I argued that they were exhibiting true singing behavior. Shortly afterwards, Andrew Spencer asked me an intriguing question: why does a vocalization have to be stereotyped in order to qualify as a song? Are there any birds that sing non-stereotyped songs?

I can’t find an answer in the scientific literature.  Among researchers, the definition of bird “song” (as opposed to “call”) has been pretty controversial over the years, but the question of stereotypy isn’t the controversial part.  Most authors simply take for granted that bird songs should be stereotyped — or “crystallized,” in the terminology often used for learned songs.

And perhaps for good reason: I haven’t been able to find any clear-cut examples of unstereotyped courtship song.  Sure, there are the “subsongs” of young, inexperienced males, and birds may sing variable songs at different times of year — but it seems that when an adult male really needs to impress a female, in almost any species, stereotype becomes important.

This may be because females, at least in some species, prefer stereotyped songs.  In the Zebra Finch, for example, the degree of stereotypy varies depending on what the male is doing. When he’s by himself, each song is different from the last, albeit in very subtle and minor ways. But when a female shows up nearby and the male’s got courtship on his mind, he begins to sing directly to her, and those subtle differences go away: each song now becomes a precise copy of the last. Woolley and Doupe (2008) showed that females prefer this stereotyped courtship song over the more variable undirected kind — meaning that females are listening not just to how males produce their songs, but how they reproduce them.

Is stereotypy easier or harder?

Which demands more of the singer—stereotyped or non-stereotyped vocalizations?  My guess would be the former; it seems intuitive that having to produce a sound multiple times in precisely the same way, without any tolerance for variation, should be the more difficult task. But when it comes to demands on the listener, things might be the other way around. Recognizing a sound is likely to be easier when the sound only takes one form. If the singer is trying to send the same message in a slightly different way each time, it actually requires the listener to recognize a class of similar sounds rather than a single sound – presumably a more difficult cognitive challenge.

Let’s consider an example from human speech.  A common word like “birthday” is not going to sound exactly the same every time you say it. Sometimes you might say it quickly, sometimes slowly; sometimes while laughing or when your nose is stuffed up; sometimes with your voice rising toward the end of a question. Sometimes you might even sing it. In all these cases, the spectrogram of your voice saying “birthday” is going to look different—and yet, every single time, our brains reliably classify these sounds as renditions of the the same word. That takes some mental firepower—it’s difficult for computers to do, which is why speech transcription software remains imperfect.

Perhaps it’s no coincidence that the best examples I could find of birds that rarely give stereotyped vocalizations are also the most intelligent birds: parrots and ravens.  Nothing that these birds say in the wild meets the classic definitions of bird “song,” but they are apparently lifelong vocal learners — ravens, like parrots, can be taught to speak in captivity — and they apparently recognize other individuals of their species by voice, even though no two utterances are likely to be precisely the same.  Compare these calls from a Lilac-crowned Parrot in Mexico:

Four examples of calls from one Lilac-crowned Parrot; they sound identical but vary slightly on the spectrogram. Rancho Santa Barbara, Sonora, Mexico, 6/24/2010.

Here’s an unedited sample of consecutive calls from the same bird, showing how different types of calls grade into one another:

Sequence of Lilac-crowned Parrot calls, showing variation. Same bird as above.

Even these parrots have the ability, and apparently the need, to reproduce almost exactly the same call over and over, even if they don’t do it with quite the same precision as most other birds.  Is this lack of perfectionism a sign of intelligence?  Or merely a sign that they’re not in an amorous mood?  Are there any species in which the females are attracted to vocal innovators instead of virtuoso self-imitators?

At the moment, nobody really knows.

Do Evening Grosbeaks Sing?

Do Evening Grosbeaks Sing?

A while back, I asked in a blog post whether Violet-green Swallows sing — and I answered that they do, because they produce complex repeating strings of stereotyped syllables, even if those syllables don’t sound like much to the human ear.  Now it’s time to ask the same question of the poor, misunderstood Evening Grosbeak, whose vocalizations have often been vastly underappreciated, even by the authors of the BNA account:

Unlike most of their fellow oscines, Evening Grosbeaks do not make much use of the longer, more complex, learned vocalizations (i.e., songs) that characterize the vocal behavior of most songbirds. The Evening Grosbeak seems to be a songbird that doesn’t regularly use songs.

The BNA authors discuss the possibility of Evening Grosbeak song at some length, and by and large I think they do a thorough job of it.  However, much of their analysis rests on a fundamental assumption that song in songbirds must be musical, preferably with trills and warbles attached — and as we’ve already seen many times, that just isn’t true. Not until the end of the article do they really strike pay dirt:

Some observers (L. Elliott pers. comm.; G. Budney pers. comm.) have recorded long series of flight calls, sometimes intermixed with trills, from Evening Grosbeaks. During these sequences, calls (or pairs of calls) are repeated rhythmically at intervals of about 1 s during bouts that can last as long as twenty minutes. Budney reports that long bouts are a regular occurrence at dawn in the Sierra Nevada of California. Perhaps these aggregated, rapid-fire calls act as the functional equivalent of songs during the dawn chorus.

I too have heard song-like strings of flight calls from Evening Grosbeaks (for example, this bird), but I actually feel the best candidate for song in this species is its long strings of trill calls, not flight calls.  In the spring of 2008, Evening Grosbeaks had come out of the higher elevations to invade a number of towns in southern Colorado, and when I stopped in the town of Norwood, I found the place infested with them (along with Pine Siskins and Cassin’s Finches galore).  One male was sitting up atop a small aspen tree, broadcasting his trills to the world:

Evening Grosbeak song, Norwood, CO, 5/13/2008.

These trills are variable, but not randomly so.  In fact, they sort into three well-defined types that we’ll call A, B, and C.  They sound almost identical to the ear, but not quite; if you listen carefully, you can distinguish the order of the male’s calls on this 20-second cut: ABC, ABC, ABC, ABC, ACB, CAC.  When we zoom the spectrogram in, we can see that the differences are subtle, but distinct:

First three calls of the above recording, zoomed and cropped.

The “A” and “B” calls are quite similar at first glance, composed of backwards-L-shaped upslurs, while “C” is obviously distinctive, composed of zigzag backwards-N-shaped notes.  The key distinction between “A” and “B” is that “A” is polyphonic, while “B” is not.  It’s nearly impossible to determine this by looking at the fundamental (that is, the lowest and darkest of the three vertically stacked sounds on the spectrogram), but it becomes obvious when looking at the harmonics (the upper two versions) — the horizontal parts of the call are doubled in “A” and single in “B.”

These differences are not random.  All the “A,” “B,” and “C” calls are stereotyped — that is, they are perfect copies of one another, reproduced with exquisite precision.  Compare the first five renditions of each call on the recording:

The first five "A" calls on the above recording.
The first five "B" calls on the above recording.
The first five "C" calls on the above recording.

The Norwood bird isn’t the only Evening Grosbeak who’s been caught singing on tape.  The Macaulay Library has a couple of recordings [1 2] of singing males recorded a few days apart in central Oregon by Thomas Sander.  The first cut is rather brief, including only sixteen individual trills, but they too fit nicely into “A,” “B,” and “C” categories, much like those of the Norwood bird (click here to see a labeled spectrogram).  The second cut is more extensive, and more impressive — for most of its first three minutes it features an apparently solo singer who incorporates six different trill types instead of three (labeled spectrogram here).

Obviously, more study of Evening Grosbeaks is needed to determine the actual function of these suspiciously song-like vocalizations, but I strongly suspect that they function as male advertising calls.  Hopefully Aaron Haiman, who is currently studying Evening Grosbeaks, can get to the bottom of some of this!

Do Violet-green Swallows Sing?

Do Violet-green Swallows Sing?

Violet-green Swallow, Nicasio, CA, 6/6/2008. Photo by Len Blumin (Creative Commons 2.0).

The Violet-green Swallow has long been one of my favorite birds.  Perhaps that’s because it is the only one of the seven widespread North American swallow species that I didn’t see regularly when I was growing up in eastern South Dakota.  Perhaps it’s the wonderful way that the colors blend on its iridescent back.  Perhaps it just reminds me of my beloved Rocky Mountains.

At any rate, most of the reasons I like Violet-green Swallows have always had to do with what they looked like, not what they sounded like.  I was fairly familiar with their calls, or so I thought, but I had never really listened to them closely.

Even so, I was astonished to find that the current scientific literature says that Violet-green Swallows don’t sing at all.  “I detected no recognizable, repeating series of syllables which could be interpreted as a song,” wrote Charles Brown in a 1983 paper in the Wilson Bulletin.  An undergraduate at the time of the research, Brown is now legendary as a swallow researcher, having spent two decades studying Cliff Swallow coloniality in Nebraska.  But after writing the BNA account on Violet-green Swallow in 1992, Brown apparently hasn’t published anything further on the species.  Nor does anyone else seem to have studied its vocalizations.  And so, according to the literature, Violet-green Swallows don’t sing.

Really?  No song?

It struck me as unlikely that Violet-green Swallows should lack a song, first because I thought I had heard complex song-like vocalizations from them, and second because the Tree Swallow, a close relative of the Violet-green, definitely sings.  It’s rare for one member of a species pair to sing and not the other.  (However, it’s not unprecedented.  Eastern Bluebirds sing a complex, melodious song; Western Bluebirds reportedly just string call notes together.)

So I went looking through my collection of Violet-green Swallow recordings.  Interestingly, most of my recordings matched Brown’s original findings: during the day, the species tends to give three kinds of calls, and even though some of them sound “complex” and I had taken them for song, it appears that none of them are stereotyped–meaning they’re not carbon copies of one another.  Instead, each rendition of a call varies slightly from all the others, like in the calls of House Finches or Rosy-Finches.  As Brown noted, if these calls were going to be strung together in some kind of song, one would expect to see stereotyped versions, possibly repeated in some kind of predictable pattern.

However, note the caveat in what I said above: during the day.  Some swallow species (including Tree Swallow and Purple Martin) sing dawnsongs that apparently differ significantly from anything they say when the sun’s up.  Brown’s work did not reveal the existence of a dawnsong in Violet-green Swallow, but it did note the passing mention of “predawn song-flights” in The Birder’s Handbook and “apparent chee-chee calls” starting as early as 2:20 a.m., according to Bent’s Life Histories.

And that led me to a most interesting recording in my collection.  At 4:20 in the morning on the 2nd of  July, 2008, when the sun was only barely lighting the eastern horizon, I was hiking with a friend up the Loch Vale trail in Rocky Mountain National Park, hoping to reach a Black Swift nesting site before dawn.  Just as we reached the Loch, I heard chirping from far overhead, and I immediately turned on my recorder, hoping to catch a Black Swift coming off its night roost.  But no: the chirping was too regular, too relentless, not high-pitched or clear enough.  The bird was completely invisible as it circled, singing endlessly against a backdrop of stars, but I was pretty sure it was a Violet-green Swallow.  Here is a snippet of the recording:

The bird went on like this for at least several minutes without pausing.  When I first looked at the spectrogram of the above snippet, it looked like the daytime calls had: a jumble of similar notes, each slightly different than the last, showing no apparent rhyme or reason.  But then I zoomed in and started looking very carefully, and sure enough, a pattern emerged:

The calls are stereotyped: all the “A” phrases are basically identical to one another, as are the “B” phrases, etcetera.  Furthermore, although the order is variable, there’s a strong tendency to stick to a couple of basic patterns.  In other words, this is classic song, crystallized and rule-bound, no matter how disordered it sounds to our slow human ears.

You may not want to give them any prizes for their melody, and you may not even hear them unless you rise long before the sun.  But make no mistake: Violet-green Swallows do have a song–one that seems to have gone almost unnoticed until now.

Humming Their Own Tune

Humming Their Own Tune

In the bird world, there’s usually a pretty big difference between vocalizations that are learned and those that are not learned. By and large, learning birds can produce much fancier songs than their learning-impaired cousins – perhaps because coding music directly into the DNA takes up a lot of genetic “disk space,” introducing limits on the complexity of genetically-determined vocalizations.

Like many members of its family, this Anna's Hummingbird sings an extremely complex, learned song. Photo by Nathan Rupert (Creative Commons 2.0).

If you flip through a North American field guide, you might notice that the birds in the front half of the book (ducks, hawks, owls, gulls, woodpeckers) tend to have pretty simple vocalizations, whereas all the most acclaimed avian singers (wrens, thrushes, finches, mockingbirds and thrashers) are in the second half of the book. This is no coincidence. First, birds in the order Passeriformes (the huge order that encompasses the second half of the field guide) sport a uniquely complex set of muscles to control their syrinx, enabling them to perform much more spectacular feats of vocal gymnastics. Second, with the important exception of the flycatchers, most North American passerines learn their songs.

However, the learning of complex songs isn’t restricted to the so-called “songbirds.”  In fact, some of the best examples of learned, complex songs come from a family that isn’t in the Passeriformes at all: the hummingbirds.

To people in most parts of North America, this may come as quite a surprise.  That’s because our most widespread and familiar hummingbirds — Ruby-throated, Black-chinned, Broad-tailed, and Rufous — actually don’t sing songs at all; their vocalizations are limited to a variety of chip notes and buzzes, and produce their territorial sounds mechanically, with trilling wings or chirping tails in display dives.  But to those who live along the West Coast or in the southwestern deserts, the soft but astonishing song of the Anna’s Hummingbird is a familiar sound:

And Anna’s is no fluke.  Behold the vocal stylings of a Green-throated Mountain-Gem, a Central American relative of the Blue-throated Hummingbird:

Laboratory experiments have demonstrated that at least Anna’s Hummingbirds learn their songs, and as one would expect, the songs vary regionally as a result.  Although not all hummingbird songs are as complex as the examples above, the variation in songs can be tremendous.  Check out Xeno-Canto’s collection of recordings of Reddish Hermit, a lekking hummingbird from South America.  A quick perusal of nearly two dozen spectrograms will show that no two songs are alike.  Now, South America is a huge continent, and a species as wide-ranging and vocally variable as Reddish Hermit might well be split in the future — but take a look at these three recordings, all from the same biogeographic region (the Guianan Shield):

All show a similar repeated downslurred series, but each is spectrographically unique, and those differences are easily detected by the ear.  The differences are evidence of song dialects — local variants that we would expect to see in any population with learned songs.  (Anna’s and other singing hummingbirds have these song dialects too, but the differences between dialects are a little easier to see in a hummingbird with a simpler song.)

Many species of North American hummingbirds sing, including Costa’s, Blue-throated, Magnificent, White-eared, Broad-billed, Violet-crowned, and probably also  Buff-bellied.  In the tropics, the chorus of singing hummingbirds can sometimes be absolutely bewildering.  Next time you’re in singing hummingbird territory, keep your ears peeled for these all-too-often overlooked, underestimated melodies.

Rattles, Claps, & Burp-clicks

Rattles, Claps, & Burp-clicks

Buff-collared Nightjar. Photo courtesy of Manuel Balcazar Lara (click for link).

Perhaps the single species I most wanted to audio record on my recent trip to Sonora was the Buff-collared Nightjar.  I posted last year about the mystique of hearing this bird north of the Mexican border, where it is extremely local and rare.  In southern Sonora, by contrast, it is abundant, and I heard its préstame-tu-cuchillo song every single night of the trip.

Although the song of the species is well known, its other sounds are not.  The Birds of North America account on this species says “Calls, typical of genus, are various chuck or clucking notes; and quirr. Calls very similar to those given by Whip-poor-will. No known recordings of calls. Female known to give only chuck calls or clucking; no song. … Not known to wing-clap as other caprimulgids do.”  Howell and Webb’s Mexican field guide says that calls include “a low, clucking chuuk and kruk kruk, kruk…, and harder, clucking chatters.”  These descriptions give the impression that Buff-collareds may have a pretty impressive call repertoire, but without recordings, of course, it’s difficult to be sure.

I am pleased to share with you a couple of cool audio clips that may help resolve (or perhaps merely deepen) the mysteries surrounding the calls of the Buff-collared Nightjar.  The first was recorded in 1986 and resides in the archives of the Macaulay Library.  It was recorded by Geoff Keller, one of the foremost nature sound recordists in America, and the first four minutes of it are probably the finest recording I’ve heard of Buff-collared’s primary song.

Right at the end of the cut, something remarkable happens:

(Click here to hear the original)

The first time I heard this, I thought that Geoff’s microphone had rolled downhill right in the middle of one of the bird’s song strophes.  It sounded like a mechanical failure of the sound equipment.  But after listening carefully a second time, I realized that the crickets in the background keep chirping undisturbed throughout the disturbance and after.  I did a little research and discovered that Curtis Marantz, another fine sound recordist, had listened to the same cut before me and added some notes to Cornell’s database: “The recording concludes with what appears to be a series of wing-claps and some clucking or clicking calls (if not a noise produced by the wings).”

At first I was somewhat skeptical of this claim, since wing-clapping hadn’t been reported from the species, and also because of the bizarre nature of the sound, which alternated low “claps” with higher “rattles.”  But then I contacted Geoff Keller by email to ask him about the circumstances surrounding this recording, and he replied:

You have hit upon one of my most memorable recordings of my entire career….  As for the sounds at the end of the recording, I too agree they are wing-claps. I have now since heard many similar wing-clap sounds from other members of the Nightjar family.

Even more interesting is what Geoff witnessed after the end of the recording:

After the bird ended his series of territorial calls, the presumed male flies away (that is when the wing-claps are heard). However, the bird wasn’t finished. It circled around and landed once again just a few meters in front of me. There apparently was a female present, and the two nightjars began yet another series of most unusual sounds, which almost certainly would have been courtship vocalizations. This series of vocalizations were very different from the display/advertisement call of the male … I seem to remember “purring sounds” and “gurgling” like noises. I am presuming there was a female close by in the darkness, but I do not really know for sure. I do know for certain that the nightjar was unaware of my presence, as I had been holding tight under the cover of a mesquite tree for many minutes, and had entered this position while the bird was calling from the opposite end of his breeding territory some 100 meters away.

Unfortunately, we don’t have recordings of the courtship sounds that Geoff heard in the field that night.  But when I was in southern Sonora, I had my own remarkable encounter with a Buff-collared Nightjar, which resulted in another interesting recording.

It was about 9:00 PM, quite a while after sunset, and my Mexican guide Rene and I were hiking by headlamp down a trail through some scrubby forest on the north slope above Rancho Santa Barbara.  We had just stopped to listen (successfully) for Spotted Owls, and I had my recording equipment ready to go, although it was turned off, when Rene came around a corner and a bird flew up in front of him, clucking and growling.  I immediately recognized the vocalizations of a nightjar, as I’d heard similar sounds from Common Poorwills and Mexican Whip-poor-wills in distraction displays.  I turned my recorder on, and as I did so, the bird flew away from Rene and closer to me — landing about 10 feet in front of me on the path.  It took me a couple of seconds to find it in the headlamp and point the microphone at it properly, and during that time it made a bizarre series of quiet sounds, alternating burps and clicks and low gulps.  When I finally got a look at the bird in the headlamp, I had just a moment to marvel at how obvious the buff collar really was.  For these few seconds (the second half of the recording below), the bird was sitting on the ground without visibly moving, so it definitely was not making any of these sounds by wing-clapping.  Then it flew off at the end the way it had flown in, with a couple of gruff clucking calls.

Over the next week, I tried many times to record more calls from Buff-collared Nightjars, but I had scant luck.  However, I did hear these odd burp-clicks again on a number of occasions, from many different individuals — always at the beginning of a song bout.  When a male nightjar was about to start singing for an extended period, he would give a series of these burp-clicks for about 10 seconds, which would lead right into the first rendition of his normal song.  After that, he would repeat the song for a long time without any calls in between — only the first song in each bout had the special introductory notes.

Perhaps the most interesting thing about what I recorded is that when I asked Geoff Keller to listen to it, he didn’t seem to think it was a very good match for the presumed courtship sounds he heard in 1986.  In other words, the species probably makes even more sounds than can be heard on this page.  Geoff’s recording and mine, I think, establish Buff-collared Nightjar as by far the most vocally versatile nightjar in the western United States — but that’s just based on the tiny bit we know of it.  What else do Buff-collareds say?

If ever there was a bird I desperately wanted more recordings of, this is surely it.

Wings of Thunder

Wings of Thunder

Andrew’s recent post on Spruce Grouse sounds made this YouTube video into a particularly nice find.  Shot by birding guide Khanh Tran in Washington state, it documents the double wing-clap display of the “Franklin’s” subspecies of the Spruce Grouse, which is the form found in the Pacific Northwest, north to central British Columbia and Alberta.  The video will play in high resolution by default; I recommend clicking on the fullscreen icon.  At the end, the wing-clap portion of the video is replayed in slow motion, and appears to show that the bird makes the sound by clapping its wings together above its back as it descends:

These wing-claps, aptly compared to gunshots in the Sibley guide,  have never been documented in the widespread “Taiga” Spruce Grouse (subspecies canadensis).  Most female grouse are thought to be extremely picky about their mates’ displays; males that don’t exactly match their expectations may not get a second look.  Thus, display differences are thought to contribute to reproductive isolation of a couple of other closely related grouse species (Gunnison vs. Greater Sage-Grouse  and Dusky vs. Sooty Grouse).  The presence or absence of a couple of loud wing-claps seem like a reasonable mechanism for separating “Franklin’s” from “Taiga” Spruce Grouse.

Compare the above to this excellent (but lower-resolution) video from northern Minnesota that manages to capture, I think, all the displays of a nominate “Taiga” Spruce Grouse, including all the ones Andrew posted about.  Note the similarity of the display flight as the male comes down from his tree perch — he “stalls out” much like the Franklin’s does and changes wingbeat speed, but resists all temptation to wing-clap.  Instead he makes the much fainter “drumming” recorded by Andrew, which is essentially inaudible in this video.

If that video didn’t satisfy your thirst for watching “Taiga” Spruce Grouse, check out the sequels (1 2 3).

Very little information on the display of Franklin’s Grouse is easily available; Khanh Tran’s video appears to be the only one of its kind online.  The Macaulay Library has a fairly extensive collection of Spruce Grouse recordings (both audio and video), but they all apparently pertain to the Taiga form.  Although Franklin’s and “Taiga” Spruce Grouse were considered separate species at one point, they were lumped in the mid-20th century due to reports of hybridization and introgression in their contact zone in British Columbia and Alberta.  As far as I can tell, no new information on this contact zone has surfaced in the scientific literature for more than fifty years, so there’s not much I can say about it.  However, molecular phylogenies of the grouse by Gutierrez et al. (2000) and Drovetski (2002) both provided genetic evidence for a split of Spruce Grouse, and David Sibley recently listed it as one of the 10 most likely upcoming splits.  But the group hasn’t been as well-studied as the Blue Grouse complex (now split again into Dusky and Sooty Grouse), so the checklist committee may want to reserve judgment for now.

Meanwhile, recordists wanting to make a difference in taxonomic research might schedule a trip to that legendary contact zone in Alberta and northern BC!

lWeoWtEacBE
They Taste Like Turpentine

They Taste Like Turpentine

Copyright Andrew Spencer, April 2010, Boot Cove, Maine

Or so I’ve been told.  Supposedly the only way that Spruce Grouse can get away with being so remarkably “stupid” is the fact that since they eat spruce needles they taste absolutely vile, vaguely reminiscent of turpentine.  Since, obviously, I haven’t actually tried Spruce Grouse myself I can’t comment on what they actually taste like, but it certainly sounds like as good an explanation as any…  However, despite their not tasting very good this is still a highly sought-after species, with a well developed reputation as a hard to find bird.  Here is my take on how you can find one…

Depending on who you ask, how to actually find a Spruce Grouse is a matter of debate.  Some people say it’s easiest in the winter, when deep snow forces birds to the edge of the road.  Others may say it’s in the later summer, when females herd their young through the spruce-fir.  If you ask me, though, I would say that it’s in the early spring, when the muffled wingbeats of displaying males echo softly through the forest.

First off, though, I should correct a common misconception about Spruce Grouse displays.  They do NOT include extremely low pitched hooting, as has been reported in many sources (e.g., Sibley).  This misconception apparently has its roots in and article by Greenwalt (1968), and this error has been echoed through many field guides until recently.  The displays of Spruce Grouse (the males at least) are entirely non-vocal, and the low pitched vocalizations referred to in most sources apparently are in reference to Dusky or Sooty Grouse.

I should also note that all the displays I write about below are in reference to the nominate subspecies of Spruce Grouse.  The taxon found in the northwestern part of the lower 48 and adjacent Canada (“Franklin’s” Grouse) has a different display, and one I am not familiar with.

The main display of male Spruce Grouse (and the loudest, and thus easiest to hear from a distance) is simply the sounds of the wings whirring as it flies from a perch about 15 feet in a tree to the ground, and then back up to the tree.  The specifics of the wing noise varies, though, between the descent and the ascent: during descent the bird flies normally, until it nears the ground, when it suddenly rears up nearly vertically in the air and the pace of the wingbeats picks up noticeably.  During the ascent the wingbeats are more powerful and faster, but even in pitch throughout the flight.

While neither of these wing noises are especially loud, in the early spring boreal woodland (where there tends to be very little noise) it can carry for quite a distance and be a good way to find them.

Spruce Grouse flight display descent, Boot Cove, Maine, April 2010
Spruce Grouse flight display ascent, Boot Cove, Maine, April 2010

Once you’ve located the displaying grouse, if you watch it long enough you may well notice some other, quieter and more subtle displays.  One that was frequently given by a bird I observed for a couple of hours in Maine consisted of the bird lifting both its wings about a quarter way to horizontal and then beating them against the sides of its body, producing a muffled but quite audible “thump”.  This sound is apparently not described in BNA, but seems to be a quieter version of the two loud “gunshot-like” thumps of the display of “Franklin’s” Sprcue Grouse.

Spruce Grouse wing thump, Boot Cove, Maine, April 2010

The other display that I observed from Spruce Grouse in Maine is what BNA calls the “tail-whoosh”, where the bird opens its tail and closes it rapidly, producing a slightly metallic swishing noise.   It is also surprisingly loud for a sound being given by just the tail of an otherwise stationary bird.  Compared to the flight displays and wing thumps, the tail-whoosh is a rarely given noise, at least during my observations – I heard perhaps a half-dozen total during two hours.

Spruce Grouse tail-whoosh, Boot Cove, Maine, April 2010
The Mysterious American Tree Sparrow

The Mysterious American Tree Sparrow

American Tree Sparrow, 2/11/2007. Photo by Eric Begin (Creative Commons 2.0).
American Tree Sparrow, 2/11/2007. Photo by Eric Begin (Creative Commons 2.0).

A frequent topic of discussion on this blog is what we don’t know about bird sounds.  Another favorite topic is how amateur recordists might help solve mysteries — and advance science — by recording common birds in their own backyards.  Now, as most of North America languishes in the middle of a deep, dark winter, I’d like to point out a golden opportunity for citizen science — a chance to answer questions about a bird that many people know, but few really understand.

I never used to pay much attention to American Tree Sparrows.  In the places I lived, they weren’t common enough to be really familiar, but they weren’t rare enough to be noteworthy either.  For the first couple of years that I recorded bird sounds, I made no particular effort to record them, even though they can be found in winter with ease not far from my house.  I just didn’t think they had much to say.

Boy, was I was wrong.

In fact, American Tree Sparrows appear to have one of the most varied vocal repertoires of any sparrow.  I’ve recorded winter flocks on about a dozen occasions now, and listened to a good number of recordings at the Macaulay Library.  The more I listen, the more mystified I become.

The most distinctive winter vocalization of the American Tree Sparrow is the “flock call,” described by many authors as a two- or three-syllabled musical note:

American Tree Sparrow flock calls, Yuma County, CO, 12/27/2008.
American Tree Sparrow flock calls, Yuma County, CO, 12/27/2008.

In and of itself, I find the flock calls interesting, because they sound so different from anything I hear from other sparrows, and because the spectrogram shows them to be so complex.  But the more recordings of flock calls I made, the more confused I got, because it started to look like no two flocks give the same flock calls:

American Tree Sparrow flock calls, Yuma County, CO, 12/27/2008.
American Tree Sparrow flock calls, Yuma County, CO, 12/27/2008.
American Tree Sparrow flock calls, Lincoln County, SD, 12/13/2009.
American Tree Sparrow flock calls, Lincoln County, SD, 12/13/2009.
American Tree Sparrow flock calls, Brown County, SD, 12/15/2009.
American Tree Sparrow flock calls, Brown County, SD, 12/15/2009.

The incredible variety between individuals (and within individuals) strongly suggests that the flock calls of American Tree Sparrows are learned, not innate.  This is interesting and unexpected; as far as I know, complex learned calls are unknown in any of the Tree Sparrow’s close relatives.

Even more interesting is that the limited sample of recordings I’ve studied seems to hint that flockmates give flock calls that are, if not identical, at least broadly similar — while a flock just down the road might sound different.  Will further recordings support this observation or disprove it?  Either result would raise further questions.  Do Tree Sparrows learn their flock calls on the breeding grounds, during migration, or on the wintering grounds?  Do they change their flock calls over time?  If they learn from flockmates, are flock calls a way of keeping the same group of birds together all winter?  If so, why?  What happens when a bird with a different kind of call joins a flock?

At first glance, the situation surrounding these complex, apparently learned calls bears more resemblance to the vocal repertoires of some cardueline finches than to the vocal repertoires of any other North American sparrow.  Unraveling the entire mystery would be a good dissertation topic for some motivated doctoral student in ornithology.

But I’m short on motivated doctoral students at the moment.  Here’s my question: can amateur recordists get a start on solving these questions?  I’d like to find out.

If you’ve got recording equipment and ready access to American Tree Sparrows, I challenge you to get out and make some recordings of your local flock.

  1. Take notes out loud while you are recording (not the entire time, of course; it’s necessary to let the birds speak uninterrupted for at least part of the recording).  In your notes, mention the date, the location, the weather, and the species — and most importantly, try to say what you observed the birds doing, and which sounds correlated with which behaviors, and which individuals were vocalizing when.
  2. If you’ve got a local flock that sticks around most of the winter, follow it over time and pay attention to how many birds it includes.  Do flocks split and re-merge?  Do they stay separate over the course of the winter?  If the number of sparrows in your hedge varies from 5 to 50 and back all winter, we can surmise that flocks split and merge.
  3. Let me know of what you are doing via email.  If people actually do this and we collect enough data, we might be able to answer some of the basic questions about these flock calls, and we might be able to put together a paper for publication.

Anybody out there up to the challenge?

Murder Most Foul

Murder Most Foul

Eleventh of May, 2009, just before 11 AM: I was walking down the road in upper Carr Canyon in the Huachuca Mountains of Arizona, hoping to find something interesting to record.  A Dusky-capped Flycatcher was calling occasionally; some distant Yellow-eyed Juncos and Western Tanagers were singing; but the day was beginning to heat up, and bird activity was waning.  Near where I parked my car, I heard some quiet high-pitched squeals, but they didn’t seem to belong to anything in particular.  For a moment I got excited when a pair of Buff-breasted Flycatchers drove off a pair of Brown-headed Cowbirds that had been, I guessed, “casing the joint” — but this interaction was brief and quiet and I got none of it on tape; nor could I find the flycatchers’ nest.

A minute later, from back near my car, I noted that high-pitched squealing again.  Belatedly, I realized it sounded like nestlings.  Eager to record some begging calls, I headed for the sound, which was coming from near the top of a short oak, and turned on my microphone.

At first it just sounded like baby birds being fed:

Carr Canyon, AZ, 5/11/2009.
Carr Canyon, AZ, 5/11/2009.

But soon it became clear that something else was going on.  There was more activity in the tree than you’d expect from parents feeding nestlings — at least two or three birds were fluttering agitatedly in the crown, but I couldn’t see what kind they were, or what exactly they were doing.  It started to sound less like begging calls and more like distress calls:

Same as above.
Same as above.

And then, suddenly, a large dark bird took off from the tree with something dangling from its bill.  Behind it came a smaller bird in hot pursuit:

Same as above.
Same as above.

The birds landed in the open for a moment, long enough for me to see that the nest robber was a male Brown-headed Cowbird, and the frantic parent a Hutton’s Vireo.  Then the cowbird took off with the nestling and the Hutton’s went after it, far out of my sight.

But the squealing at the nest continued.  After a moment I risked walking towards it, and discovered the female cowbird pecking furiously at the contents of the nest, while another Hutton’s Vireo, or the same one, flitted around it and scolded it ineffectually:

Hutton's Vireo adult scolds and nestling distress calls during predation by Brown-headed Cowbird. Same recording as above.
Hutton's Vireo adult scolds and nestling distress calls during nest predation by Brown-headed Cowbird. Same recording as above.

Within a couple of minutes, the squeals stopped, and I could see the female cowbird eating something out of the nest.  After another minute she fled the scene, leaving the adult vireo alone with the ruined nest, and me as a witness to a particularly brutal version of a very rare event.

It has long been known that Brown-headed Cowbirds will occasionally destroy the eggs of their host species instead of parasitizing the nest.  It is rarer for cowbirds to attack nests after the eggs have hatched, but even so, the removal of nestlings by cowbirds has been documented one or two dozen times in the literature.  In some of these cases, the cowbirds have been seen to eat the nestlings.  However, the vast majority of all such attacks have involved solo females.  In only two or three cases has nest predation involving male cowbirds ever been documented (see Igl 2003 and the references cited therein).

Why do cowbirds do this?  One fascinating line of thinking is the “mafia hypothesis,” which holds that cowbirds come back frequently to check on the eggs they have laid in other species’ nests — and if they find the cowbird egg has gone missing (presumably because the host parents have recognized it as an imposter and ejected it), the cowbirds destroy the nest in retaliation (Hoover & Robinson 2007).  By forcing the host parents to build a new nest, the cowbirds may be giving themselves another chance to parasitize it at a later date.

I can’t comment on the validity of the mafia hypothesis, but I can say that what I witnessed was fascinating, and a little disturbing — and yet another reason to follow up on odd, unidentified squeaks in the forest.