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Author: Nathan Pieplow

Florida’s Online Sound Archive

Florida’s Online Sound Archive

Looks like I missed this news when it came out at the end of 2012, but I just found out about it via the Xeno-Canto forum. The Florida Museum of Natural History has put its huge collection of bird sound recordings online in digital format for the first time. According to the museum website, the collection contains over 20,000 recordings of about 3,000 bird species, making it the Western Hemisphere’s second-largest collection in terms of species and third-largest in number of recordings.  It’s the biggest single addition to the internet’s bird sound collection in many years.

I spent a little time cruising around the website, and I have some suggestions for better browsing:

  1. Get your scientific names ready! The database doesn’t contain English names at the moment. And even the scientific names are sometimes way out of date — for example, all the California and Canyon Towhee recordings are lumped together under the old name Pipilo fuscus.  (California Towhee became Pipilo crissalis in 1989, and Melozone crissalis in 2010, so the name P. fuscus is oooooold).
  2. When you want to look through some results, you might want to click on “Table Layout” instead of “Vertical Layout.”  The Vertical Layout puts the genus in bold letters at the top of each search result, but buries the species name way down in a list of information, third from the bottom.  It’s annoying. Table Layout makes it much easier to browse search results that contain multiple species.  Plus it shows you more information about each recording, if you use the horizontal scroll bar at the bottom of the screen.

Overall, it’s great to see this collection online, and I’ll be visiting it regularly from now on.

Describing Variation in Bird Sounds

Describing Variation in Bird Sounds

Three-wattled Bellbird, Costa Rica, 4/13/2008. Remixed by snowmanradio from original photo by Ryan Kozie (Creative Commons 2.0).

Bird sounds vary on many levels.  Naturally, they vary from one species to the next. But they can also vary within a species — say, between birds from different geographic regions.  And they can also vary within a geographic region — say, between one individual bird and the next.  And they can also vary within an individual bird — say, if that individual happens to have a repertoire of multiple songtypes.  And they can even vary within one songtype of one individual bird — say, if the bird fails to reproduce that same songtype exactly each time it sings.

When talking about variation, it would be nice to be able to distinguish exactly which kind of variation we mean.  I propose a vocabulary like the following.

Differences between individuals: variable vs. uniform

I’ve started using the word variable to describe sounds that show high levels of individual variation, and uniform to describe sounds with low levels of individual variation. In other words, variable sounds differ from one bird to the next; uniform sounds are the same in all members of a species.

Variable sounds (differing between individuals)

A good example of a variable sound is the mewing call of the Spotted Towhee.  This sound takes a great many forms across the range of the species. Even in the same location, the calls of different individuals may differ sharply.

Uniform sounds (the same between individuals)

The song of the Chuck-will’s-widow is highly uniform: that is, it varies little across the entire geographic range of the species.  If you’ve heard one Chuck-will’s-widow, you’ve pretty much heard ’em all.

Differences within individuals: Plastic vs. stereotyped

Plastic sounds differ slightly each time they are produced, even by the same bird. Stereotyped sounds are always the same when made by the same bird.

Plastic songs are typical of young birds, but some sounds of certain species remain plastic into adulthood, like the “Vreet” call of the House Finch.  In adult birds, plasticity may vary with situation and season. Highly stereotyped versions of song tend to be associated with courtship. Plastic versions may be heard in winter, when levels of breeding hormones are lower.

Plastic sounds (differing within individuals)

Notice how these calls are almost never the same twice:

Stereotyped sounds (the same within individuals)

Most bird songs are stereotyped, at least during the breeding season: each time the individual repeats a given songtype, it produces a precise copy of the previous rendition. Note that sounds can be variable and still stereotyped; Eastern Meadowlark songs vary greatly across their range, and even within individuals (in the sense that each individual has multiple songtypes). But consecutive renditions of the same songtype tend to be identical down to the smallest details — the songtype never changes when the same bird repeats it.

The four vocabulary words I’ve defined here (variable, uniform, plastic, stereotyped) aren’t quite sufficient to describe all the different types of variation.  Things get complicated when you start talking about repertoires of songtypes, truncations of stereotyped songs, or mosaics of geographic variation of different song features.  But maybe this is a start.  I’ll be happy to hear what people think.

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.

The Seven Basic Tone Qualities

The Seven Basic Tone Qualities

Nothing has created more confusion about how to describe sounds than tone quality.

Tone quality is the distinctive voice of a sound — the thing that allows you to tell the difference between a violin and a trumpet when they’re both playing the same note. It comes in very handy when identifying birds by sound, but people have tended to differ in their notions of how to describe it.  Today, we’re going to break sounds down into just seven basic qualities, which in combination make up the huge variety of sounds that birds can create.

And here they are:

Whistled sounds

Whistles are the most basic and common type of bird sound. They appear on the spectrogram as simple nonvertical lines. Non-bird sounds with a whistled tone quality include typical human whistling, and the sounds of flutes and piccolos.  Bird examples are plentiful:

Hooting sounds

Hoots and coos are just low-pitched whistles, less than 1 kHz in frequency, that appear at the very bottom of the spectrogram. They resemble the sound made by blowing across the top of an open bottle, and they are typical of the voices of doves and large owls.

Clicking sounds

Instantaneous bursts of noise sound like clicks, pops, or taps, and appear on the spectrogram as vertical lines. The ticking of a clock, the drumming of a woodpecker’s bill against a tree, the bill snap of an angry flycatcher, and the ticking song of Yellow Rail all fall into this category.

Burry and buzzy sounds

When a whistle rises and falls very rapidly in pitch, it forms a squiggly line on the spectrogram and sounds trilled, like a referee whistle. If the squiggles are tall and fast enough, they sound less musical, more like an electric buzzer. What all burrs and buzzes have in common is the presence of very rapid repeated elements, resulting in audible “beats”. This makes them very similar to (and in some cases indistinguishable from) trills.
The beats in burry and buzzy sounds are often so rapid that they are not individually visible on the spectrogram. The result is a well-defined shape on the spectrogram that is vertically thicker than the thin line of a whistle. Such sounds often have a hoarse, grating quality to the ear.

Noisy sounds

Noisy sounds contain noise—that is, random sound at multiple frequencies, which looks like television static on the spectrogram and sounds like static to the ear. Unlike buzzes, noisy sounds tend to have faded, blurry edges on the spectrogram, and they often almost stretch all the way to the bottom and the top of it.

Non-bird sources of noise include rushing streams and waterfalls, and the English speech sounds “s” and “sh”.  Noisy bird sounds tend to be described as “rough” or “harsh,” like the alarm chatters of wrens and the hissing of angry swans and geese.

Nasal sounds

Many bird sounds are actually combinations of multiple simultaneous whistles on different pitches that the human brain typically perceives as a single sound (because of the mathematical relationship between the frequencies of the different whistles). This is characteristic of the sounds we identify as having a nasal tone quality. The individual whistles are called partials.  Non-bird examples include police sirens, the whine of mosquito wings, and the sounds of oboes and violins.

Polyphonic sounds

Many birds can produce two separate sounds simultaneously, one from each lung. When birds use this ability, the two original sounds blend into one polyphonic sound. Polyphonic sounds are diverse, encompassing a number of different tone qualities, but with practice, they can be consistently distinguished from all other types of sounds by ear.

On the spectrogram, polyphonic sounds may look like nasal sounds, with stacks of partials, but if the spectrogram is high enough in quality, they can usually be distinguished by having partials that are dissimilar in shape, irregularly spaced, or simultaneously rising and falling.

The quality of most polyphonic sounds is either distinctively metallic or distinctively whiny.

metallic: If the polyphonic notes are very brief or contain monotone segments, they tend to sound metallic, like certain versions of the Hooded Oriole call, some versions the “squeaky gate hinge” songs of Brewer’s Blackbird and Common Grackle, and the shimmering melodies of thrushes like the Veery.

whiny: If the polyphonic notes do not contain any monotone segments, they tend to have a whiny quality, like the Pine Siskin and Blue-gray Gnatcatcher calls, as well as the common calls of House Finch and the flight calls of meadowlarks.

Obviously, these seven tone qualities are very broad categories. Some of them grade into one another, and some of them occur in combination — e.g., a note may be simultaneously burry, noisy, and nasal.  But this is the basic vocabulary we’ll use to start discussing the qualities of sounds.  More to come!

Changes in Speed and Pitch, and Multi-noted Series

Changes in Speed and Pitch, and Multi-noted Series

Now that we’ve looked at the five basic pitch patterns and the four basic song patterns, let’s explore a couple of ways to extend and combine the vocabulary we’ve learned.

Changes in speed

One of the basic questions we ask of any bird sound is, “are the notes slow enough to count, or too fast to count”?  Sometimes, the answer is both.

Some bird sounds change in speed. If the elements in a series are more closely spaced on the spectrogram as you move from left to right, then they are growing more closely spaced in time, which means that the series accelerates. If the elements grow farther apart, the series decelerates.

Here are a couple of examples. The song of the Wrentit is a series of notes that accelerates into a trill, while the drum of a Yellow-bellied Sapsucker starts as a trill of tapping notes, and slows into a series.

Changes in pitch

Phrases, series, warbles, and trills can also change in pitch. For example, a warble might sound upslurred if it shows an overall trend towards higher notes. Similarly, a series might fall in pitch if each note starts slightly lower than the last, even though each individual note may be upslurred.


Overslurred series are quite common among bird sounds. Here are two examples:

Changes in both speed and pitch

Many sounds change in speed and pitch at the same time. A quick glance at the spectrogram of the Sora’s whinny shows us that it’s an overslurred, decelerating series with an early peak:


Here’s a decelerating, downslurred series of upslurred whistles:

And here’s a phrase accelerating into an upslurred warble:

Multi-noted Series

Sometimes the repeated elements in a series may themselves consist of multiple notes. A two-noted series sounds like a two-syllabled word repeated, such as “peter peter peter;” a three-noted series, like a three-syllable word repeated, such as “teakettle teakettle teakettle.”

Examples of two-noted series

Examples of three-noted series

Yes, there are four-noted series too

With the basic vocabulary that I’ve introduced in these three posts, we can describe the pattern of almost any bird sound.  But there’s more to bird sounds than just pattern.  Stay tuned for the next installment in the series.

The Four Basic Song Patterns

The Four Basic Song Patterns

In the last post, I covered the five basic pitch patterns, introducing some vocabulary to help distinguish between different types of individual notes.  Today I’m going to introduce some vocabulary to help distinguish between different types of groups of notes — that is, different types of songs.

The four song patterns are based on two simple questions:

  1. Does the bird ever sing the same thing twice?
  2. Are the notes slow enough to count, or too fast to count?

Together, these two questions delineate four basic patterns: phrases, series, warbles, and trills.  These four simple patterns, individually and in combination, give us a precise way to describe almost any type of complex bird sound.

  • Phrases are clusters of unique notes that are slow enough to count;
  • Series are clusters of repeated notes that are slow enough to count;
  • Warbles are clusters of unique notes that are too fast to count;
  • Trills are clusters of repeated notes that are too fast to count.

“Too fast to count” is a somewhat subjective criterion, but as a general rule of thumb, it’s any speed over about 8 notes per second.  Here are some examples of each pattern, so you can practice hearing the differences.

Phrases

In these examples, each note is different from the one before, and the notes are slow enough to count.

Series

In these examples, each note is the same as the one before, and the notes are slow enough to count.

Warbles

In these examples, the notes are all different, and too fast to count.

Trills

In these examples, the notes are all the same, and too fast to count.

In the next installment in this series, we’ll look at some ways to combine and extend this vocabulary to cover almost any type of bird sound pattern.

The Five Basic Pitch Patterns

The Five Basic Pitch Patterns

The “How to Read Spectrograms” section of this blog is in desperate need of an upgrade, so today I’m starting a series of posts to help people describe and visualize sounds as simply and clearly as possible.  Our first topic: pitch patterns.

To identify birds, you don’t need musical training.  You don’t have to name the notes that a bird is singing.  You only have to recognize whether the pitch of a sound is rising, falling, or staying the same.  Five simple patterns allow us to describe most sounds:

  • Monotone sounds do not change in pitch, and appear horizontal on the spectrogram.
  • Upslurred (or rising) sounds rise in pitch, and appear tilted upward.
  • Downslurred (or falling) sounds fall in pitch, and appear tilted downward.
  • Overslurred sounds rise and then fall in pitch, appearing and sounding highest in the middle.
  • Underslurred sounds fall and then rise, appearing and sounding lowest in the middle.

Let’s listen to some examples.

Monotone sounds

These sounds are characterized by horizontal lines on the spectrogram. Even if those lines are very short (as with the Townsend’s Solitaire call), it’s still easy to hear that the sound isn’t going up or down, just remaining on the same pitch from start to end.

Upslurred sounds

Listen to these sounds and practice hearing how they rise in pitch.

Downslurred sounds

Listen to these sounds and practice hearing how they fall in pitch.

Overslurred sounds

One of the most common pitch patterns in bird sounds is the overslur, which rises and then falls in pitch.  These sounds are often mistaken for upslurs or downslurs, so listen carefully to hear both the initial rise and the ending fall.

Underslurred sounds

This is not a common pattern, but when heard, it is distinctive.

These five basic pitch patterns are the starting point for talking about the different types of notes that we hear from birds, but there’s much more to discuss.  Next up, we’ll discuss the four basic patterns of repetition and speed.

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.

Common and Hoary Redpolls

Common and Hoary Redpolls

Apparent Hoary Redpoll, eastern Ontario, 2/4/2009. Photo by Seabrooke Leckie (CC 2.0).

Last winter, in the Great Redpoll Invasion of 2012-2013, huge numbers of these little Arctic birds pushed farther south than anytime in recent memory, prompting a surge of interest in redpoll identification and taxonomy.  My good friend Andy Boyce even got people talking about whether Hoary and Common Redpolls are separate species, or identifiable forms, and the many resulting discussions taught me (and others, I’m sure) a lot about how we define and detect species boundaries.  And the conversation hasn’t quit: Tom Johnson and Luke Seitz are contributing with a redpoll identification article in the July/August issue of Birding.

During the course of these discussions, a couple people argued that Common and Hoary Redpolls have been shown to differ in vocalizations.  To verify this claim, I set out to track down the relevant peer-reviewed literature, including a paper in Swedish, two key publications in Russian, and a book in German.  It took some six months, but thanks to the help of a terrific interlibrary loan crew (and some assistance from Albert Lastukhin in Russia), I finally managed to get copies of all the sources.  My dusty old fluency in Russian came in handy, as did my one year of college German.  (Oh, and Google Translate.)

The original claims of differences in the literature

In 1981, Maria Zablotskaya provided a detailed spectrographic and behavioral analysis of the vocalizations of Common Redpoll; the following year, she teamed up with Boris Veprintsev to do the same for Hoary Redpoll.  These authors are often cited as having found differences in the sounds of the two species, but it’s important to note that they did not explicitly address the issue of species differences (or species boundaries) at all.  The first paper treated Common Redpoll only; the second paper discussed Hoary Redpoll only, with only a few passing comparisons to Common.  They named several more calls for Common than they did for Hoary, but this is likely due to the fact that they spent less time with Hoaries and had fewer recordings available for analysis.  A careful reading of both papers (along with Ernst 1998) shows that there probably aren’t any sounds in the repertoire of one species that don’t have an equivalent in the other species.  This doesn’t necessarily mean that the species sound the same, but it does mean that they give similar types of calls.

In the face of doubt about whether the two redpoll species should be lumped, a couple of authors stepped forward in the mid- to late 1980s to defend the two-species concept.  Ulf Molau’s (1985) “The redpoll complex in Sweden” focused on plumage and measurements, but also made the following important claims about vocalizations (translated from the Swedish by me, with help from Google Translate):

Common and Hoary Redpoll differ not only in size and plumage characters, but also in vocalizations. The low-key contact sounds uttered on the ground or in a tree crown (or in a cage) may in Common Redpoll be described as a catchy “chit-chit-chit.” Hoary Redpoll’s contact vocalization is a rougher, almost House Sparrow-like “chirp-chirp.” Similar differences also exist in the familiar “flight song” which is rougher and more metallic in Arctic Redpoll. Both Common Redpoll races flammea and cabaret are, however, completely identical as far as vocalizations are concerned.

These conclusions are based on Molau’s own observations of wild, banded, and long-term captive birds.  He did not provide spectrograms.

Marc Herremans (1989), on the other hand, does provide spectrograms in support of the notion that the redpoll species differ in at least two vocalization types.  He says of the contact calls:

Common [gives a] characteristic “machine gun”-like low and pure chatter, che-che, che-che-che, che-che-che-che-che. Arctic [=Hoary] sounded clearly slower, higher-pitched and less pure, djeet, djeet-djeet, djeet-djeet-djeet.

He illustrates these with spectrograms from two individuals of each species:

Contact calls of two Common Redpolls, from Herremans 1989

Contact calls of two Hoary Redpolls, from Herremans 1989

The two Commons (D and E) resemble each other on the spectrogram, and the two Hoaries (A and B) more or less resemble one another, but there are clear differences between the species, according to this graphic.

Case closed?  No, not quite.

You see, redpolls are cardueline finches, and Paul Mundinger showed way back in the 1970s that in this subfamily, many calls are learned, not innate.  Members of pairs change their call types to match one another, as a bonding mechanism.  Mundinger (1979) paired a captive female Common Redpoll with a male Pine Siskin, and a male Common Redpoll with a female Eurasian Siskin.  In both pairs the two members ended up with nearly identical flight (contact) calls.  In these cases Mundinger wasn’t certain which individuals had changed their calls to match the other’s, but he thought it likely that the male Pine Siskin had switched calls to match his redpoll mate, and that the male redpoll had matched calls with his Eurasian Siskin partner.

Herremans certainly knew of Mundinger’s work.  In fact, he replicated it: he demonstrated that three individual redpolls (a male Common, a female Common, and a female Hoary) all adopted identical “breeding calls” when paired with one another in captivity.  But he didn’t seem to appreciate the implications of this work, which called his earlier claims of species differences into serious question.  Herremans seemed to believe that call matching only happened with “breeding calls” among mated pairs, but Mundinger’s work was with the flight/contact calls, and at least in one species (Pine Siskin), he showed that even two males matched calls when caged together.  (Two females, however, did not.)

So redpoll calls are learned.  Does that mean there can’t be consistent differences between the species?  Not at all.  But if the calls are learned AND flockmates match one another’s calls, we might expect to see flock-specific call dialects.

And that’s exactly what we see when we compare online recordings.  There’s tremendous variation from one Common Redpoll to the next:

 Common Redpoll, Okanagan Co., Washington, 12/22/2011. Click to listen  Common Redpoll, Grand County, Colorado, 1/15/2013. Click to listen  Common Redpoll, Parkland County, Alberta, 4/22/1974. Click to listen  Common Redpoll, Lac La Biche County, Alberta, 6/6/1981. Click to listen

And from one Hoary Redpoll to the next:

Hoary Redpoll, Safety Sound, near Nome, Alaska, 5/14/2013. Click to listen Hoary Redpoll, Kougarok Road, near Nome, Alaska, 6/4/2013. Click to listen Hoary Redpoll, Dalton Highway, Alaska, 6/10/2006. Click to listen

Within flocks, redpolls tend to sound the same.  Between flocks, they tend to sound different.  These differences can be pretty large in geographic scope: I got recordings of three different redpoll flocks last winter from three different Colorado counties, and they are all pretty similar to one another.  But they are quite different from the redpolls in Washington and Alberta.

This is the pattern we would expect to see if flockmates match one another’s calls.  We would expect birds in one flock to converge on a common pattern, while birds in another flock converge on a different common pattern.  If redpolls respond preferentially to birds of a similar call type (like crossbills, their closest relatives within the Carduelinae), that would explain why Herremans’ captive Hoary Redpolls showed little response to the calls of wild Commons flying by.  Maybe it was because they weren’t conspecifics — but maybe it was just because they weren’t flockmates.

So…

There may be consistent differences between the vocalizations of the redpoll species.  Perhaps they use vocal differences to reject mates of the wrong species.  Perhaps we can use differences to tell the species apart.  But we can’t do that on current knowledge.  There simply aren’t enough available recordings to document the limits of variation within species, in order to hash out the differences between species, if they exist.

There’s also the question of whether Hoaries and Commons in the same winter flocks may match each other’s calls.  We don’t know whether they do, but given the willingness of these species to match calls of even Pine and Eurasian Siskins in captivity, it’s at least possible.

So it’s premature, I think, to try identifying redpolls by voice.  But that’s no excuse to ignore it.  We need to learn more about the calls of these birds, and for that we need more recordings.  The next time the redpolls come south, I hope they meet a barrage of microphones.

The Warbler Guide

The Warbler Guide

(Updated 7/10/2013 to include discussion of the audio files now available for download)

Princeton University Press recently sent me a review copy of Tom Stephenson’s and Scott Whittle’s The Warbler Guide, published this month.  This is one of the most remarkable books about bird identification that I’ve seen in recent years.

The quick summary:

  • It’s huge. Only one inch shorter and 3 ounces lighter than the “big” Sibley Guide.  You won’t be slipping it into your jacket pocket.
  • It has TONS of photographs — 38 photographs of Blackburnian Warbler in that species’ account, not counting the blown-up vignettes and comparison photos of similar species, or the photos in the wonderful flight comparison plates at the back of the book.
  • It’s got spectrograms — illustrating an average of 4 song types per species, plus the “chip” and the “flight call.”  At last, a field guide that gives bird sounds the attention they deserve!
  • It’s groundbreaking.  There’s more information here on warbler identification than you can learn in a year (if you don’t already know it) — and the authors have come up with multiple original ways to present it, many of them quite brilliant.

Disclaimer

I got the fine opportunity to review this book in part because it puts so much emphasis on identification by sound, including by spectrogram — which is what this blog is all about.  As you know, I’m currently at work on my own field guide to bird sounds. In some ways, The Warbler Guide treads some of the same ground, but it does so in its own way, and I have no connection to the authors or the publisher.

Visuals

The visuals in this book are tremendous.  The quantity and quality of the photographs outstrips anything I’ve seen in a field guide.

Maybe the best part is the comparison pages, most of which are called “finder guides”.  You want all the warbler heads on one plate?  All the undertails?  All the side views?  All the song spectrograms?  All the flight shots?  This book’s got comparison plates for all of these and more.  These pages alone are worth the cover price.

Layout

The book’s layout can be confusing, contributing to an overall sense of “information overload.”  For example, the Blackburnian Warbler species account proceeds as follows:

  • Pages 1-2: photos of bright Blackburnians;
  • Page 3: more photos of bright Blackburnians, plus photos of some comparison species (in this case, Yellow-throated and American Redstart);
  • Page 4: how to age and sex Blackburnians, plus range maps;
  • Pages 5-6: spectrograms: Blackburnian on the left, confusion species on the right;
  • Pages 7-8: photos of drab Blackburnians;
  • Page 9: more photos of drab Blackburnians, plus comparison species;
  • Page 10: a full-page photo of a Blackburnian, just to keep the number of pages even.

The design makes it hard to tell when you’re “home” in a species account — that is, when you’re at the beginning.  And the ubiquity of comparison species, both in photos and spectrograms, blurs the borders between accounts even further.  If you, like me, are in the habit of scanning photos rather than words when looking for a particular species, then abandon all hope of navigating this book with ease.  (If you’re in the habit of scanning words, you’re still in some trouble, because all the photos are helpfully labeled.)  The only thing that saves this book from complete organizational disaster is the decision to order the species accounts alphabetically rather than taxonomically.  Normally I’m not in favor of this, but here, it’s a life-saver.

Spectrograms

The big news is that this book has spectrograms!  That fact alone makes me want to shout with joy from the rooftops.  At last we can see the sounds we’re describing.  This is the first major attempt to use spectrograms for identification since at least the 1980s, and it is long overdue.

It’s also a watershed moment for birding by ear.  A lot of people will use this book to decide whether spectrograms are worth using.  I fervently hope they will think so.  But based on the way the sounds are taught and presented, I fear that some readers, especially casual birders, may persist in the prevailing misconception that spectrograms are difficult, and “for experts only.”  If this happens, it will be the fault of the authors’ vocabulary.  A choice as simple as using the term “element” instead of “note” sends the message that song identification is a technical endeavour, not an intuitive one.

Their narrow focus on warblers both hurts them and helps them.  It allows them to simplify the discussion to three tone qualities — “clear, complex, and buzzy” — which is a simple and helpful distinction.  But the focus on warblers also tempts them to divide all songs into “phrases” and “sections.”  This terminology is great for explaining the difference between, say, Nashville and Tennessee Warbler songs, but it becomes very awkward when applied to, say, Canada Warbler, forcing the authors to write “many Phrases, almost all 1 Element” instead of the much simpler “almost never repeats a note.”  And their descriptions of “Expanded” and “Compressed” elements are so opaque that I fear they may do more harm than good.  I fear the same for the section on distinguishing between flight calls.

Again, though, they get the visuals right.  The spectrograms are high-quality, and underneath each one is a series of symbols intended to give a sense of how the song actually sounds.  When it comes to the pitch and rhythm of the sounds, these symbols are pretty intuitive, and they had me hearing the sounds in my head almost immediately.  I don’t know if they’ll work for everybody, but they might provide a “stepping stone” to help beginners translate between picture and sound.

Sounds

The book is accompanied by a downloadable playlist of audio files.  In a couple of years, we’re going to forget that serious books on bird ID were ever published without accompanying audio files.  And we’ll get used to paying more: it costs an additional $5.99 to download the audio collection.  You can purchase it separately from the book if you like.

The audio collection mirrors the book exactly.  The sound file named 180 a Blackpoll  Chip Call.mp3 accompanies spectrogram a on page 180, making it easy to go back and forth between audio and book.  If a particular sound appears more than once in the book (due to being included on multiple comparison pages), then it appears more than once in the audio collection as well. Unfortunately, the naming convention for comparison songs is confusing: 165 d Black-and-white  Blackburnian.mp3 is the Blackburnian song shown on the comparison page for Black-and-white Warbler.  There’s no Black-and-white Warbler in the audio clip.

The audio files are generally high in quality.  They are very short — a single song or a single call — and have been assiduously cleaned of background noise.  One really cool thing is that the audio files use spectrograms as the “album art,” so on most devices, the appropriate spectrogram pops right up when you play the song.  This little feature, more than any other aspect of the entire project, has the potential to get people visualizing sounds and change the way they listen.

One downside to the audio aesthetic is that it forces a narrow focus on single songs. There’s little mention of patterns of delivery — whether consecutive songs are similar or different — which can be useful for ID at times.  More distressingly, the single-serving recordings of chips and flight calls provide zero information about the range of variation in each species’ calls, and the careful scrubbing of background noise makes some of them sound unnatural.  Compared to Evans and O’Brien’s CD-ROM of flight calls, The Warbler Guide’s recordings are far easier to listen to and compare.  But Evans and O’Brien’s longer and more natural-sounding clips, even though they often roar with noise, provide lots more information to the ear.

Biology

This book is pretty much all identification, all the time.  There’s very little about biology and behavior — only what the authors deem useful in identification.  Many warblers employ a two-category song system, in which different categories of songs are deployed in different patterns for different purposes.   The research into these song systems is extensive, complex, and mostly absent from this book.  Many will applaud the narrow focus on identification, but I, for one, am sorry that the book teaches me little more about these fascinating birds than simply how to tell them apart.

The bottom line

All in all, this book is a must-have for serious birders.  Beginning and intermediate birders should also check it out, and not be too discouraged by the sheer volume of information.  I am confident that this book will enhance the way people look at warblers.  I am less confident, but ardently hopeful, that it will enhance the way they listen to warblers as well.