Nathan Pieplow – Page 12

Murder Most Foul

20 December 2009 Nathan Pieplow

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:

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:

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:

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.

On Spectrogram Settings

15 December 2009 Nathan Pieplow

Today’s post is the promised follow-up to my post on the history of spectrograms. I want to explain some basic concepts of spectrographic analysis so that I can clear up some common misconceptions and explain why some things may not always look quite the way you expected.

In “A Brief History of Spectrograms” I mentioned that the original Kay Electric Co. Sona-Graph had two settings: narrow-band and wide-band. Nowadays, spectrograms are produced from digital recordings on computer software that allows much more control over the width of the “band.” But our control over how spectrograms look isn’t complete, and here’s why.

The Trade-off: Frequency Resolution vs. Time Resolution

The first thing every student of spectrograms should understand is that the more accurately you measure the frequency of a sound, the less accurately you can know when it begins and ends – and vice versa. The reason for this is a fundamental part of the mathematics behind our spectrographic analysis, and I won’t attempt to explain it here.

The main effect of this principle is that modern spectrograms are broken up into small rectangles called “windows” which are the basic “pixels” of the image. As anyone familar with digital images knows, tiny pixels make for a sharp, clear image, and big pixels make for a blocky, poorly defined image. Unfortunately, spectrographic windows are necessarily rather big and blocky. You can shorten them in one dimension, but if you do, they automatically get longer in the other dimension. Depending on your settings, you can end up with “pixels” that are long, thin rectangles, instead of squares.

Modern spectrographic analysis software generates these “windows” behind the scenes and then automatically “smooths” the resulting spectrograms so that they seem to have higher resolution than they actually do. This smoothing algorithm is basically an after-the-fact Photoshop trick, and although it’s very helpful in making visual sense of a spectrogram, it’s important to realize that the smoothing doesn’t actually increase the amount of information in the spectrogram; it’s just the computer’s best guess at what the spectrogram would look like if the resolution were higher.

Here’s a series of spectrograms of the exact same recording (an American Tree Sparrow call). On the left is the raw, unsmoothed spectrogram. On the right is the smoothed version. From top to bottom, the time resolution increases and the the frequency resolution decreases.

Window size: 23.2 mS × 61.9 Hz

American Tree Sparrow call, Minnehaha County, SD, 12/13/2009. Left: raw (unsmoothed) spectrogram; right: smoothed version. — American Tree Sparrow call, Minnehaha County, SD, 12/13/2009. Left: raw; right: smoothed.

Window size: 11.6 mS × 124 Hz

Same recording. — Same recording as above. Left: raw; right: smoothed.

Window size: 5.8 mS × 248 Hz

Same recording as above. Left: raw; right: smoothed.

Window size: 2.9 mS × 496 Hz

Window size: 1.45 mS × 991 Hz

Note that I am not “zooming” in or out on these calls; the time and frequency axes remain precisely the same in all of the above spectrograms. All I’ve done is decrease the width of the analysis windows, which automatically increases their height.

See how tremendously different the smoothed spectrograms look from one another? The difference between the second and fifth is particularly striking. In the second, we clearly see a series of horizontal sidebands in the call. In the fifth, we see only an extremely rapid series of vertical, click-like notes. How can these possibly be spectrograms of the same call? Which one is right?

They’re both right. All the spectrograms above are accurate, in that they’re all displaying different (accurate) interpretations of the same data. A complex tone comprised of whistled partials (like in the second spectrogram) and a rapid series of clicks (like in the fifth spectrogram) can be the same sound. Once a series of clicks becomes fast enough, we hear it as a harmonically complex tone. This shouldn’t be surprising when you consider that the human vocal cords are just making a series of very fast clicks, but the result is a wonderfully rich, harmonically complex sound: the human voice.

Here’s a spectrogram that shows basically the same phenomenon. Artificially generated for demonstration purposes, it’s the spectrogram of a decelerating series of groups of clicks. When the groups of clicks are closely spaced, at the beginning of the spectrogram, they don’t show up as groups of clicks, but as a single pure tone with sidebands. Only later, when the distance between clicks reaches a certain threshold determined by the window size, does the spectrogram begin to resolve them separately:

There’s been some debate in the technical literature over whether sidebands like these are a “real” phenomenon, or just an “artefact” of spectrographic analysis. For anyone interested in the debate, Watkins (1968) is required reading. If you’d like more information on where the debate went after 1968, email me. Suffice it to say that, for all intents and purposes, the winners were those who argued that sidebars were real.

Although this post was on the technical side, I hope it was useful to you. Comments are welcome (including those telling me I’ve gotten something horribly wrong).

How I Listen

11 December 2009 Nathan Pieplow

David Sibley was gracious enough to reply to my recent post on Buff-collared Nightjar, first in a comment on my blog, then yesterday in a post on his own blog. He takes issue with me on at least one point:

Nathan Pieplow seems to suggest that, for decades, observers have misidentified Vermilion Flycatchers as Cassin’s Kingbirds, and then mistakenly written that Cassin’s Kingbird sounds like Buff-collared Nightjar.

I guess I did seem to suggest that, but I didn’t really intend to. Instead, I think I meant, “an authoritative source once misidentified a Vermilion Flycatcher as a Cassin’s Kingbird, and for decades, authors have perpetuated the error by simply citing the published assertion that Cassin’s Kingbird sounds like Buff-collared Nightjar.” Given what David wrote in his comment and his post, even the latter assertion by me is a little unfair to him at least, and perhaps to many of the other people I mentioned in that post, since David didn’t just blindly repeat the conventional wisdom; he had field experience to back it up. (However, see his post for an interesting discussion of how the conventional wisdom might have influenced his field experience.)

Overall, though, regardless of who (mis)identified what, David has started a very interesting and, I think, important discussion about a sea change that may be occurring in how birders listen to bird sounds. He writes:

I learned bird songs decades ago through countless hours of field experience, supplemented by listening to a few recordings, reading detailed descriptions, and talking to other birders. It was a subjective, holistic approach to bird songs that led to a sort of gestalt style of identification – after you hear a sound often enough the identification just becomes second-nature.

Now, it still takes countless hours, but birders have a wealth of technological aids, allowing them to study and compare bird sounds with an ease and immediacy that was never possible before. In the modern world of ipods, sonagrams, and websites like xeno-canto, birders can examine the bird sounds directly, objectively, and in great detail. This may lead (as Nathan Pieplow admits) to a slightly greater emphasis on differences in pattern rather than the more subjective and hard-to-describe differences in tone.

Given how suggestible we are, and how tiny things can influence our perception, the detail-oriented objective approach to bird sound identification is probably better and more accurate. A similar shift happened in sight identification a couple of decades ago, and that shift can also be linked to technology. In the 1980s it was rapidly improving photographic equipment and optics that allowed more detailed study and comparison of living birds than ever before, leading to a whole new approach to identification based on feather details, molt, etc.

It may be that with modern technology Cassin’s Kingbird is no longer such a source of confusion with Buff-collared Nightjar. If so it has merely been replaced by another species (Vermilion Flycatcher) that is less easily sorted by the modern style.

This gives me a lot to think about. Perhaps the different ways in which we learned our bird sounds might provide insight into how David Sibley and I listen to sounds differently. He learned sounds in the field; I learned them on the floor of my bedroom in South Dakota when I was in high school, playing the Peterson Birding By Ear tapes over and over again. Those tapes (which remain the best resource I’ve ever seen for people who want to learn bird sounds on their own) didn’t take a holistic, all-at-once approach; instead they took an analytic approach, grouping similar sounds together and then pointing out key field marks or “handles” — here a distinctive tone quality, there a distinctive rhythm — to distinguish sounds within the groups.

I’ve used this same basic approach to sound identification ever since: recognize a pattern, then focus on a piece of it. The pattern gets you to the right group; the pieces narrow the identification to species. Tone quality is part of this analysis, but not the most important part.

In fact, in some ways I think I place a pretty low priority on tone quality. For several years now, I have been convinced that tone quality is the slipperiest attribute of sound: the hardest to analyze perceptually, the hardest to describe. And I think tone quality is responsible for most of the disconnect between most descriptions of sounds and the sounds themselves. I de-emphasize it precisely because it is so difficult to categorize. Other attributes of sound are much easier to describe and compare, so those are the ones I focus on.

For the most part, I’m just doing what works for me, but I hope it works for other people as well. I really do believe in the objective, analytic approach. On the whole, I don’t think I can say it any better than I said it at the end of my Birding article:

When we set about describing a bird sound in words, we should avoid the temptation to describe how the sound makes us feel or what it reminds us of, since those things exist in us, not in the sound. Instead we should strive to describe what is there: what can be measured with a stopwatch, pointed out on a sonogram, and defined in an empirical fashion. I cannot claim yet to have accomplished this with pinpoint accuracy. But I firmly believe that it can be done, and I firmly believe we should start to do it.

A Brief History of Spectrograms

7 December 2009 Nathan Pieplow

1951 – 1995: The Sona-Graph Era

In 1951, the Kay Electric Co. produced the first commercially available machine for audio spectrographic analysis, which they marketed under the trademark “Sona-Graph.” The graphs produced by a Sona-Graph came to be called “Sonagrams.” For decades, all spectrograms were Sonagrams.

The original Sona-Graph had two settings, “narrow-band” and “wide-band.” The narrow-band setting was more accurate in terms of frequency, but less accurate in terms of time, and it tended to create spectrograms that looked rather anemic, like they had been drawn with a thin pencil:

Alarm calls of Lawrence's, Lesser, and American Goldfinches. From Coutlee 1971, Animal Behavior 19:559.

Here’s a classic Sonagram on the wide-band setting, which sacrificed frequency resolution for time resolution, making spectrograms look calligraphic, as though they had been drawn with a wide-bladed pen held vertically:

Varied Thrush "vreee" and "churrr" calls. From Martin 1970, Condor 72:453.

Note the discoloration of the spectrogram “boxes” above. It’s a reminder that the Sonagrams created by the original Sona-Graph were actual physical artifacts on paper. In this case Martin cut them out and pasted them onto another sheet of paper to create his figure, which was a common practice at the time.

Another common practice was to cover the paper Sonagram with a sheet of acetate and trace the spectrogram with a pen to produce figures for publication. Many authors preferred this method because it created “cleaner” results — the pen eliminated background noise and equalized levels in the bird’s sound:

Yellow-eyed Junco song. From Marler & Isaac 1961, Wilson Bulletin 73:194.

These traced spectrograms were some of the best that could be created in their time, but they were also in some ways insidious: they resulted in a simplification and sometimes a distortion of the sound, as human artistry made “prettier” what the Sona-Graph had rendered. I tend to think that many authors of the day actually traced the spectrograms they published even if they didn’t admit to it in their Methods section: for example, the spectrograms of Coutlee above look like they may well have been traced.

Logarithm Wars

There were a few early attempts to publish spectrograms on a logarithmic frequency scale rather than a linear one, like this:

Canyon Towhee song, displayed on a logarithmic frequency scale. From Marshall 1964, Condor 66:346. — Canyon Towhee song, displayed on a logarithmic frequency scale. Note that the octaves (denoted by "c") are evenly spaced, while the kilohertz labels are not. From Marshall 1964, Condor 66:346.

Marshall was rather militant about his unconventional y-axis:

Graphs of the calls were automatically scribed by the sonagraph machine. I have rendered tracings of them on a logarithmic frequency scale of musical octaves. This equalizes pitch intervals over the entire compass of the graph. For it is pitch and not frequency to which our hearing and that of the birds respond in nature, and for this reason the gross stretching apart of musical intervals in the upper part of the ordinary sonagram is absurd!

The Golden Field Guide to Birds of North America, first edition, 1967. — The Golden Guide, first edition, 1967.

The “problem” that Marshall “solved” with his logarithmic axis is an actual phenomenon that we’ve seen before (albeit in a slightly different form): on a typical linear axis like those we use today, an octave takes up less vertical space near the bottom of the spectrogram than it does near the top. Perhaps because most scientists valued ease of measurement more than they valued ease of matching spectrograms to sounds (or, just as likely, because the Sona-Graph didn’t easily adapt to the logarithmic scale), Marshall lost this battle and the vast majority of all published spectrographs to date have maintained the linear frequency scale.

1967 – 1983: The Golden Age

A landmark in the history of American birding (and spectrograms), the Golden Field Guide to Birds of North America was the first (and to date only) major American field guide to include Sonagrams. This book, above all else, cemented the name and the notion of the “sonagram” in the consciousness of birders. Unfortunately, the spectrograms were widely considered something of a failed experiment. Stuart Keith’s otherwise mostly-positive review in the Wilson Bulletin (79:251-254) pretty much summed up the public reaction:

Another unique feature of the book is the use of sonagrams for depicting songs and calls. To my mind this is the least successful feature. While sonagrams have value in scientific studies of bird calls, their usefulness as an aid to field identification is very limited. To begin with, considerable practice is needed in order to be able to read sonagrams; but even when some proficiency is acquired, I doubt if anyone can really imagine or “hear” a new song simply by reading its sonagram. I challenge anyone who has never heard the call of a Red-bellied or a Gila woodpecker to “hear” the difference between their calls by reading the sonagrams on page 182. Admittedly it is interesting to see what a call which you already know looks like as a sonagram, but this is not the point. A field guide should teach you to have an idea of a song before you hear it. I maintain that you cannot learn bird songs from sonagrams.

I maintain that Stuart Keith was wrong on most of these points, and I hope this website will eventually prove it. I will grant him, though, that it was hard to learn bird songs from the spectrograms in the Golden Guide, which were half an inch tall and frequently quite illegible. Had they put more effort into the spectrograms in the field guides back then, who knows what earbirding powers modern birders might have by now?

1995 – present: The Digital Era

It wasn’t until the mid-1990’s that software finally displaced the Sona-Graph (albeit a fancier, updated version of it) as the audiospectrographic analysis tool of choice. Modern software continues to make spectrograms faster and more customizable: they can now be instantaneously adjusted to show finer gradations in the relative loudness of parts of the sound, using a grayscale digital display. Here’s an example of a spectrogram published recently by authors who really know how to use the modern equipment:

Anna's Hummingbird dive sounds and song. From Clark & Feo 2007, Proceedings of the Royal Society B 275:957.

Unfortunately, some modern authors fail to use the modern equipment to its full potential, preferring instead to emulate the “old” black-and-white traced spectrograms. More on that later, in another post!

You Misidentified It Wrong

1 December 2009 Nathan Pieplow

For better or worse, this sign usually means "good birding ahead." Cochise County, AZ. Photo by Tom Peck (Creative Commons 2.0).

The Buff-collared Nightjar is a little-known but highly-sought bird from Mexico that can be found in some of the remote canyons of southernmost Arizona. Seeking this nocturnal rarity can feel like a real adventure. On your way to look for it, you’re guaranteed to pass a sign warning you of terrible dangers, intended to dissuade you from wandering around in the lawless border country lest you meet humanity’s worst elements alone in a dark arroyo.

But the dark arroyos of this remote wilderness are precisely where you must venture if you want to hear the remarkable song of the Buff-collared Nightjar, an evocative rising, bubbly, knocking series that some in Mexico transliterate as préstame tu cuchillo, “lend me your knife” — one of the phrases birders most want to hear from any bird (and, presumably, one of the last phrases they want to hear from a shadowy human figure lurking in the dark thornscrub).

The song of the Buff-collar is so unique that it would seem impossible to mistake for any other bird. But in fact, in the predawn darkness in the very same canyons where the nightjar lives, a strikingly similar sound is often heard from a different bird — a flycatcher that begins its dawn song long before most birders expect day birds to be singing. Over the years, many reports of singing Buff-collared Nightjars have turned out to be flycatchers instead.

According to the classic 1964 publication Birds of Arizona by Phillips, Marshall, & Monson, the source of the nightjar-like dawn song is none other than Cassin’s Kingbird. And this assertion has been repeated by many subsequent credible sources, including Joe Morlan, Kenn Kaufmann (in both North American Birds and in Kingbird Highway), the Arizona Bird Records Committee, the BNA account of Cassin’s Kingbird, and even the Sibley Guide to Birds.

The only problem is, Phillips et al. were mistaken. The dawn song of Cassin’s Kingbird sounds nothing like a Buff-collared Nightjar. It’s the dawn song of Vermilion Flycatcher that causes the confusion. To wit:

Buff-collared Nightjar song, Santa Cruz County, AZ, 5/21/2009. Recording by Andrew Spencer.

(click here for audio)

Vermilion Flycatcher dawn song, Santa Cruz County, AZ, 5/13/2009.

Cassin's Kingbird dawn song, Santa Cruz County, AZ, 6/4/2009. Recording by Andrew Spencer.

(click here for audio)

You can see the resemblance between the first two songs on the spectrogram. Of course there are differences: Vermilion Flycatcher’s dawn song is faster and higher-pitched than Buff-collared Nightjar’s song, with a different tone quality. But the similarity in overall pattern is quite striking.

If you’re having difficulty seeing the similarity between Cassin’s Kingbird dawn song and the first two, that’s because it’s completely different. The spectrogram looks nothing like the others, and the song doesn’t sound anything like the others either. And as far as I can tell, nothing else in Cassin’s repertoire comes any closer to resembling the nightjar. However it happened, it looks to me like Phillips et al. named the wrong bird as the confusion species for Buff-collared Nightjar, and most other authors have followed suit for 45 years.

A Hybrid Hummingbird?

23 November 2009 Nathan Pieplow

Rich Hoyer has posted photos and spectrograms of an apparent Calypte x Archilochus hummingbird at his blog this morning. He’s also posted a sound file in the “mysteries” section of Xeno-Canto.

I’m no expert in the visual identification of female hummingbirds, so I can’t make too many comments on his photographs, but the vocalizations of hybrid birds are of long-standing interest to me, so his sound files and spectrograms certainly got my attention. A morning’s investigation convinced me that the sound file he posted does indeed provide good evidence that the bird at his feeder could be a hybrid, probably the progeny of a Black-chinned Hummingbird and a Costa’s Hummingbird.


Female Black-chinned Hummingbird, Moab, Utah, June 2006. Wikimedia.org (Creative Commons 3.0).		Male Costa's Hummingbird, 16 April 2009. Photo by Chris Fritz (Creative Commons 2.0).

According to the excellent Hybrid Hummingbirds page at Trochilids.com, the hybrid combination of Black-chinned x Costa’s (which seems most likely for Rich’s bird given his comments on its plumage) was documented by Short & Phillips (1966), so if the bird is confirmed to be of that mix, I believe it would be the third documented such hybrid and the second known female.

Rich has already posted some spectrograms over at his place, but I’m going to go ahead and supplement his with some of my own. Since the fine details of hummingbird chips are pretty fine indeed, I’ve zoomed these things in MUCH farther than usual and widened the filter bandwidth for better time resolution.

First, here’s the typical chip of a female Black-chinned Hummingbird:

Black-chinned Hummingbird call, Pima County, AZ, 5/13/2009.

Note the downslurred intonation and the strong partials, with the third one strongest. If this call lasted 20 times longer, we would hear its nasal tone quality. Since it’s so brief, we just hear a high-pitched, fairly clear downslurred “squeak.”

Here’s the standard call of the female Costa’s Hummingbird, first at the same zoom level as above, then zoomed out to a slightly more sane perspective:

Costa's Hummingbird calls, Maricopa County, AZ, 12/24/1988. Recording by S. Gaunt. Borror Library #16973. — Costa's Hummingbird calls, Maricopa County, AZ, 12/24/1988. Recording by Sandra Gaunt. Borror Library #16973.

Same as above, zoomed out slightly in the time axis. — Same as above, zoomed out in the time axis.

(Click here to listen to the audio at the Borror Lab’s website. It takes a bit for the bird to call.)

Obviously, the calls of Costa’s and Black-chinned Hummingbirds are extremely different on the spectrogram, and they can even be distinguished easily by ear with experience. As Rich’s spectrograms show (and my research has so far corroborated), Costa’s is the only hummingbird in the Calypte/Archilochus group with an upslurred call note (actually an overslur, as you can see above) — and the upslurred beginning of the Costa’s call is often perceptible to the ear. Black-chinned, Ruby-throated, and Anna’s all have perceptibly downslurred calls.

The calls of Black-chinned and Ruby-throated are by far the lowest-pitched, with many harmonics visible; they are less sharply inflected and therefore more musical than the calls of Anna’s Hummingbird, which start at a far higher pitch (around 9 kHz) and descend much more quickly, giving them a less musical “ticking” quality.

The hybrid at Rich’s feeder has downslurred calls with many visible harmonics, much like a Black-chinned Hummingbird, except higher-pitched and more sharply inflected:

Possible hybrid hummingbird, Tucson, AZ, November 2009. Recording by Rich Hoyer.

(again, click here for Rich’s audio at Xeno-Canto.)

By itself, the higher pitch and sharper inflection (noted by Rich’s keen ears as “too high and percussive for Black-chinned”) didn’t at first convince me the bird was a hybrid. A careful reading of Rusch et al. 1996 finds mention of a rather similar vocalization from Black-chinned Hummingbird, which the authors called the “E note,” but even this note is not high-pitched enough to match the hybrid, and it is apparently never given outside the complicated chatters that hummingbirds make when sparring with each other. The same apparently holds true for Ruby-throated Hummingbirds (Rusch et al. 2001). So Rich’s recording is at least suggestive of hybridity.

But here’s something even more interesting: not every note on Rich’s recording is identical. Most of the calls on the cut actually start with a slight but noticeable upslur:

And sometimes it is very pronounced:

Although I don’t think it constitutes proof, this definitely suggests to me that the bird has some Costa’s Hummingbird genes. Rich, I think it’s time to contact your friendly neighborhood hummingbird bander. And keep that microphone running!

Learn to Record Birds

22 November 2009 Nathan Pieplow

When I took the Sound Recording Workshop in 2004, Evening Grosbeaks were everywhere. Photo by Jean-Guy Dallaire (Creative Commons 2.0). — During the Sound Recording Workshop in 2004, Evening Grosbeaks were everywhere. Photo by Jean-Guy Dallaire (Creative Commons 2.0).

Some people have asked how I learned to record bird sounds. The answer is simple: in 2004, I took the Macaulay Library’s annual Nature Sound Recording Course in California. If you’re interested in getting into audio recording in nature, I can’t recommend this course more highly.

The price ($945 in 2010) is tremendously reasonable, given that it includes all the personal attention, intensive training, transportation to local recording locations, amazing (though rustic) accommodations, and great food that you get for the entire week of the course. It’s held in a spectacular area of the country that allows participants to record in at least four completely different habitats in as many days, all the way from the sagebrush steppe and cattail marshes of the valley floor to the high-elevation spruce-fir forest and willow carrs of Yuba Pass and vicinity.

I arrived at the Sierra Nevada Field Campus never having wielded a microphone of any kind, never having worn recordist’s headphones, never having analyzed a single bird sound spectrographically. I didn’t own a single piece of recording equipment. Luckily, however, the Library was able to lend me some. In fact they lent me several different rigs over the course of the week, so that I gained experience recording in both analog and digital formats, through both parabolic and shotgun microphones. In a way, since I had already decided I wanted to save money to buy equipment, the workshop turned into a kind of extended test drive of potential future purchases. I was able to keep all the recordings I made, and they became the nucleus of the recording library I’ve been compiling since then.

If you get a chance to participate in this workshop, jump at it. If there’s one thing this world definitely does need in my opinion, it’s more people running around pointing microphones at birds!

White-breasted Nuthatch, Part Three

21 November 2009 Nathan Pieplow

During my research for the last couple of blog posts, I’ve arrived at a surprising conclusion: when it comes to regional variation in calls, few common birds are as poorly understood as the White-breasted Nuthatch, particularly the Rocky Mountain and Pacific populations.

In the first two parts of this series we explored the “quank” calls, which are some of the most common vocalizations of the three populations, and the “fast songs.” Today we’ll investigate two more types of rapid-fire calls, the “rapid quanks” and the “hit-trills,” and then I’ll leave the subject of nuthatches alone for a little while!

Rapid Quanks

The term “rapid quank” was coined by Ritchison (1983) to describe the long strings of calls that eastern nuthatches would give in high agitation. The “rapid quanks” are a little tricky to compare among the three populations, because they grade into the regular “quanks,” the “fast songs,” and even the “hit-trills” (see below). In some ways “rapid quank” is just a catch-all term for agitated calls.

In my search through all the recordings available to me, the “rapid quanks” of Pacific birds have been the hardest to find. I suspect this is due to a relatively small sample size rather than a lack of “rapid quanking” by Pacific birds, but I’m not entirely certain of that. (Note, however, some very excited Pacific birds failing to rapid-quank on this recording.)

Above are some relatively rapid short notes from a bird near its nest in California. By comparison, the Rocky Mountain birds sound like they’re on speed:

"Rocky Mountain" White-breasted Nuthatch rapid quanks, San Miguel County, CO, 9/3/2006.

Especially when they get a little bit upset:

"Rocky Mountain" White-breasted Nuthatch rapid quanks, Clark County, NV, 9/27/2007.

As far as I know, nothing but a “Rocky Mountain” White-breasted Nuthatch ever gives notes at this frantic rate (up to 25-30/sec). This type of vocalization is highly variable, however, and I particularly recommend checking out a couple of other distinctive recordings of it, here and here (the latter recording, in particular, is repeated so many times in a row that it could be functioning as a kind of song).

When the “Eastern” nuthatches get excited, they’re still much slower, along the lines of the “Pacific” birds:

"Eastern" White-breasted Nuthatch rapid quanks, Lincoln County, SD, 9/1/2007.

This is about as crazy as they get (in response to an Eastern Screech-Owl tape):

"Eastern" White-breasted Nuthatch rapid quanks, Yuma County, CO, 12/27/2008.

For extra credit, you can listen to more fast-quanking Eastern birds here and here. Note the tendency to revert to paired notes, the “double quanks” of Ritchison (1983), whenever the bird “catches a breath.” Again, beware confusion with the diagnostic disyllabic quanks of Rocky Mountain birds.

Hit-trills

Ritchison (1983) didn’t mention a “hit-trill” vocalization, but he did identify a short contact note he called the “hit,” which is frequently extended into a trill, so I figured the name wasn’t much of a stretch. This is a rather quiet call given in close contact with other nuthatches, and it is very similar in all three populations, although like most of the other calls, it appears to increase in pitch from east to west, and increase in speed in “Rocky Mountain” birds:

"Pacific" White-breasted Nuthatch "hit-trill," Contra Costa County, CA, 3/26/2009. Note begging calls of this species also on the cut (at top of spectrogram).

"Rocky Mountain" White-breasted Nuthatch "hit-trill," Larimer County, CO, 6/3/2007.

"Eastern" White-breasted Nuthatch hit-trill, Monroe County, AR, 3/24/2006. Recording by Randy Little. Macaulay Library #129818.

Click here to listen to the above (at 1:15).

White-breasted Nuthatch, Part Two

16 November 2009 Nathan Pieplow

"Rocky Mountain" White-breasted Nuthatch, Madera Canyon, AZ. — "Rocky Mountain" White-breasted Nuthatch, Madera Canyon, AZ, 4/25/2007. Image courtesy Alan D. Wilson, www.naturespicsonline.com

Last time we looked at the most common calls of the three populations of White-breasted Nuthatch. Here in Colorado, we have both the “Rocky Mountain” and “Eastern” forms of the White-breasted Nuthatch, and I’ve heard a couple of people proclaim that any bird giving a rapid-fire series of calls is a Rocky Mountain individual, while any bird giving a single “yank” note is an Eastern. Unfortunately, it’s more complicated than that. All three populations of the species give rapid series of calls from time to time, so the first thing you’ve got to figure out is which type of call you’re listening to.

Since White-breasted Nuthatches have a lot of different call types, it will probably require several posts to discuss them all. Over the course of this series we’ll mostly follow the terminology of Ritchison (1983) in our discussion of “fast songs,” “slow songs,” “rapid quanks,” and “hit-trills.” Today’s installment looks at the “fast songs.”

Fast songs

Ritchison distinguished between “slow songs” (which we’ll explore in a later post) and “fast songs.” Fast songs consist of rapid strings of simple overslurred nasal notes at a rate of about 10 notes/second, and they appear to be similar in all populations of the White-breasted Nuthatch:

"Pacific" White-breasted Nuthatch fast song, Contra Costa County, CA, 3/26/2009.

"Rocky Mountain" White-breasted Nuthatch, Larimer County, CO, 6/18/2008. — "Rocky Mountain" White-breasted Nuthatch fast song, Larimer County, CO, 6/18/2008.

"Eastern" White-breasted Nuthatch fast song, Tioga County, NY, 3/16/1991. Recording by Steven Pantle. Macaulay Library #53158.

(click here to listen to the above recording at the Macaulay Library)

The length, rate and pitch of fast songs are fairly variable within groups, as far as I can tell, but there appears to be a general trend of increasing pitch as you move from east to west. With more investigation, these differences may turn out to be systematic.

How can you tell when you’re hearing a fast song as opposed to some other vocalization? Two ways:

Rhythm. Fast songs contain long strings of single notes (not double notes like in the “disyllabic quank” call of Rocky Mountain birds) in strict rhythm (not accelerating or decelerating).
Behavioral context. According to BNA, fast songs are given by males hoping to attract a mate; they are often sung loudly many times in a row in late winter and spring. This behavioral context helps differentiate them from some of the “rapid quanks” we will see next, since the two types of vocalizations seem to integrade.

The take-home lesson: long strict series of single nasal notes don’t necessarily identify a bird as a member of the “Rocky Mountain” group. Double notes in series, though, are a good indicator — see the last post for an example.

White-breasted Nuthatch, Part One

10 November 2009 Nathan Pieplow

Eastern White-breasted Nuthatch, 30 September 2008. Photo by Gary Irwin (Creative Commons 2.0). — Eastern White-breasted Nuthatch, 9/30/2007. Photo by Gary Irwin (Creative Commons 2.0).

Birders have known for a number of years now that White-breasted Nuthatches sort out into three distinct vocal groups in North America — Pacific, Rocky Mountain, and Eastern — following a pattern of three-way separation that mirrors those of several other bird species, including the Solitary Vireo complex (split into Cassin’s, Plumbeous, and Blue-headed) and the sapsuckers (split into Red-breasted, Red-naped, and Yellow-bellied).

However, with the exception of field guides, the ornithological literature has been silent on this point. Nobody has done a systematic study on the marked regional variation in vocalizations of the White-breasted Nuthatch. The only in-depth study on vocalizations in the species was done by Gary Ritchison in Minnesota, and so the vocalizations of the Eastern form have been the only ones described in the literature for years; they were the only ones available on commercial bird sound recordings for years too. Even though the Birds of North America account was revised by its authors in 2008, they made no mention of vocal variation, which seems a shocking oversight. Spellman & Klicka (2007) published a molecular phylogeny of the species and found evidence for four distinct clades in the species, with boundaries exactly matching those of the vocal groups (except that they found the Rocky Mountain group was divided into two clades, apparently with identical vocalizations).

Thus, since I can’t find this information anywhere else, starting with this post, I’m going to start exploring these vocal differences in some depth.

“Quank,” etc.

Here are the most common calls of the three nuthatch groups. For simplicity’s sake, we’ll always travel left to right across the country, so you’ll always see Pacific, Rocky Mountain, and Eastern birds in that order.

Pacific White-breasted Nuthach "quank" call, Contra Costa County, CA, 3/26/2009. — Pacific White-breasted Nuthatch "quank" call, Contra Costa County, CA, 3/26/2009.

Rocky Mountain White-breasted Nuthath "disyllabic quank" call, Boulder County, CO, 11/10/2009. — Rocky Mountain White-breasted Nuthatch "disyllabic quank" call, Boulder County, CO, 11/10/2009.

Eastern White-breasted Nuthatch "quank" call, Scott County, MN, 7/6/2009.

The first thing you’ll notice is that the Pacific and Eastern birds sound much more similar to one another than they do to the Rocky Mountain birds. Thus begins a theme we will see repeated many times. Spellman & Klicka found that the Pacific and Eastern birds were sister taxa, separated from one another by the less closely-related birds in the Mountain West. If this seems surprising, remember that the Solitary Vireo complex follows a similar pattern, with Cassin’s and Blue-headed Vireos looking and sounding more like each other than like Plumbeous.

The calls you see above are variable in each of the groups, so some of the differences you see between Pacific and Eastern in call length and overall inflection may not always apply. The most consistent difference seems to be one of pitch: the Pacific birds, with their more widely spaced partials, sound a lot higher-pitched than their huskier-voiced, more nasal Eastern cousins.

Identifying the Rocky Mountain birds, meanwhile, seems like a slam-dunk. Eastern and Pacific birds never make rapid-fire series of call notes, right? Well, actually, yes they do — several different kinds, in fact. I’ll be looking at those in my next post!

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