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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.

New Crossbill Compendium

New Crossbill Compendium

Red Crossbill, type unknown. Larimer County, CO. Photo by Andrew Spencer
Red Crossbill, type unknown. Larimer County, CO. Photo by Andrew Spencer

Ken Irwin is a household name — at least among the bedlamites who think untangling the mysteries of Red Crossbill call types is a fun and worthwhile activity.  Ken has haunted the seaside spruces of California’s Patricks Point State Park for years, tracking the Red Crossbills that wander in and out of the park, recording their vocalizations, capturing and measuring them, and following their nesting cycles.  According to a couple of people I talked to, he may know the individual birds by name, and rumor has it that he is close to being accepted among the crossbills as an adopted member of their tribe.

Ken is best known for discovering a new call type (Type 10), and his paper describing it is coming out in the next issue of Western Birds (which, incidentally, will also include an article on phoebe vocalizations by Arch McCallum and me — more on that later).  When I talked to Ken on the phone last year, he was also hard at work on a website that would include sound files of all the types, their excitement calls, their begging calls, their songs, etcetera.

Now that website is up, and everyone interested in crossbills should go see it.  It’s a work in progress — but even in its current form, at about 14,000 words, it’s more than a little overwhelming.  Nevertheless I recommend girding your loins and wading in.  Irwin’s site is the most important addition to the web-based crossbill literature in years.

The recordings are probably the most important contribution made by the site, and they are both good and bad.  Here’s the good news:

  • there are a lot of them;
  • they put Type 6 and Type 7 on the web for the first time (outside Jeff Groth’s original site from 1996, where all the recordings are so short and so heavily edited that they don’t really count in my opinion);
  • there are several nice head-to-head comparisons of different types;
  • most of them include lots of examples of individual birds, so that you can quickly get a strong sense of the limits of individual variation within the types;
  • they include many recordings of lesser-known vocalizations like excitement calls or “toops”, chitter calls, and songs.

Here are some things I liked less about the site:

  • The organization is confusing, and it got more so as the page went on.  The information on this one page should have been split onto several linked pages, and was apparently intended to be.  This may improve with future revisions.
  • Personally, I feel that Irwin’s word descriptions of the different calls are uneven in quality and ultimately unsuccessful, but then I have this reaction to most word descriptions of crossbill calls.
  • The recordings have been a little too heavily edited for my taste, so that the birds sound too mechanical, not quite like they would in the field.  Since Irwin typically includes 2-3 calls per individual bird, the overall effect is much better than that of Jeff Groth’s site, but if he had included longer cuts with less editing, I think his recordings could have been even more useful.
  • The spectrograms are full-contrast — bicolored black-and-white instead of grayscale — and therefore less informative than they should be.

When it comes to the science — the validity of Type 10 in general, Irwin’s boundaries for Type 10, and his conclusions regarding crossbill song — I’m going to have to postpone judgment for a while.  When I see his Western Birds paper, I’ll post again.  Until then, when you’ve got a little free time and extra brainpower, head over to his page and start the long process of digesting the enormous amount of information that he’s published — and thank him for it if you get the chance.

AOU Checklist News!

AOU Checklist News!

The North American Checklist Committee of the American Ornithologists’ Union has published the results of its deliberations on the first round of proposed changes from 2009, and it has updated the slate of proposals currently under consideration.  Here’s a quick summary of the changes that affect species splits north of Mexico.  (I won’t get into all the changes to scientific names, even though those topics are just as interesting in my opinion — you can click through to read about those yourself.)

Proposal accepted

This split will become official once the next checklist supplement is published in the July 2010 issue of the Auk.

  • Split Pacific Wren from Winter Wren. As I reported earlier, this split did indeed pass, and unanimously at that.  However, note that the names “Pacific Wren” and “Winter Wren” are not final.  The committee is considering an addendum to the proposal that would split eastern North American birds from Eurasian birds and change the names of the American species to “Western Winter-Wren” and “Eastern Winter-Wren.”  Stay tuned.

Proposals rejected

In most cases, a 2/3 vote of the committee is required for a proposal to pass.  These proposals failed to muster that level of support:

  • South Hills Crossbill. The proposal to split South Hills Crossbill (Type 9) from Red Crossbill failed on a vote of 6 “yes” votes to 5 “no” votes, with three of the “no” voters indicating that they would be open to changing their minds if presented with more data.  Two of those voters preferred to deal with the North American Red Crossbill complex as a whole, rather than splitting one type at a time, piecemeal.  Thus, most of the committee appears to accept that the different call types of Red Crossbill are likely good species, but I think it may be a while before those species appear in your field guide.
  • The split of Western Scrub-Jay. The proposal to split the interior “Woodhouse’s” Scrub-Jay (woodhousei) from “California” Scrub-Jay (nominate californica) failed on a vote of 7 “yes” votes to 5 “no” votes.  Many members of the committee felt that more data were needed from contact zones.  The tagalong proposal to split the southern Mexican subspecies sumichrasti into yet a third species gained even less committee support.  Vocal differences between woodhousei and californica have been reported, and you can expect those differences to be discussed in a future post on this blog.

New proposals

The checklist committee never sleeps.  The following splits of North American species are now under consideration:

  • Split Black Scoter (Melanitta americana) from Common Scoter (Melanitta nigra).  I wrote about this split recently.  This proposal was originally submitted in 2006 and failed to pass at that time, but the recent publication of Sangster (2009) has revived it.  Personally, I think it’s a clear-cut split, but we’ll see if the committee agrees.
  • Split Curve-billed Thrasher (Toxostoma curvirostre) into two species: the western palmeri group and eastern curvirostre group.  The proposal makes no recommendation regarding the resulting English names.  The proposal cites various genetic data, which I won’t comment on, but it also cites vocal differences, including differences in calls.  I’m a little skeptical of these differences, but I’ll investigate them in the future and report back on what I find.
  • Split Whip-poor-will (Caprimulgus vociferus) into a nominate eastern species and the southwestern arizonae species, on the basis of subtle but easily diagnosable differences in song, differences in egg coloration, and (most importantly) a hot-off-the-presses study demonstrating that the vociferus and arizonae groups may be as genetically distinct from one another as either is from the Dusky Nightjar (C. saturatus) of Costa Rica and Panama.  I haven’t been able to track down the article text yet, so I can’t say what I think of it.

As you can see, vocal differences are playing an ever-more-prominent role in taxonomic decisions.  Look for more on this topic from me in the future.

Evening Grosbeak Call Types

Evening Grosbeak Call Types

Evening Grosbeak, Soda Springs, CA, 8/3/2009. Photo by C.V. Vick (Creative Commons 2.0).
Evening Grosbeak, Soda Springs, CA, 8/3/2009. Photo by C.V. Vick (Creative Commons 2.0).

In 2004, a paper appeared in the Condor by Kendra Sewall, Rodd Kelsey and Tom Hahn that described several different variants of flight calls in the Evening Grosbeak.  Their fascinating research immediately reminded many of the work on the call types of Red Crossbill, and I heard a few people worry out loud about whether a split of Evening Grosbeak might be in the works.

But there’s no cause for worry.  The “call types” of Evening Grosbeak are not as scary as the call types of Red Crossbill.  While Red Crossbills sort into at least 10 call types in North America, Evening Grosbeaks apparently sort into just 5.  And while multiple Red Crossbill call types often occur in one area (which is part of the justification for splitting them into separate species), the Evening Grosbeak call types usually stay in fairly well-defined, separate geographic ranges.  In fact, Sewall et al. note that the five call type groups seem to match the five subspecies groups in a decades-old taxonomy.

Learning to identify Evening Grosbeak call types is a fascinating exercise, especially if you come upon a wandering flock and want to know where they likely originated.  This post aims to provide an introduction to the different “types” and how to tell them apart.

“Flight calls” vs. “Trills”

The terminology used by Sewall et al. (2004) as well as the BNA account of Evening Grosbeak distinguishes two main calls that are typically heard from the species: “flight calls” and “trills.”  Neither source mentions how the “trills” may vary among groups; this post is going to concern itself solely with the flight calls, which are the most common vocalizations.

Type 1

Range: The northern Rockies and the Cascades, from at least British Columbia south to Oregon, northern Wyoming, and the Black Hills of South Dakota.  Wanders to the northern Sierra Nevada and to Colorado.

Flight call:

Evening Grosbeak Type 1 flight calls, Whitewood, SD.
Evening Grosbeak Type 1 flight calls, Whitewood, SD, 11/20/2007.

Even though the spectrogram shows that it tends to start at a higher frequency than other types, Type 1 sounds relatively low-pitched, especially compared to Types 2 and 4.  It  has a very clear sound that is distinctive once you learn it.  More than the other types, this one reminds me of a particular Pine Siskin call (but beware!  Pine Siskins can mimic other Evening Grosbeak types in their songs).  Here’s another good recording of Type 1.

Type 2

Range: The Sierra Nevada of California; wanders at least occasionally north to southern Washington.

Flight call:

Evening Grosbeak Type 2 flight calls, California.
Evening Grosbeak Type 2 flight calls, Sierra County, CA, 6/14/2004 and 6/16/2004.

To my ear, this sounds like the clearest, most purely whistled type, even clearer than Type 1, but it is distinctly higher-pitched and more piercing than Type 1.  Type 2 is quite similar to Type 4 and the two may be difficult to distinguish by ear in the field (see below).

Type 3

Range: Boreal forests of Canada east of the Rockies and in the northeastern United States.  Wanders south throughout the East.

Flight call:

Evening Grosbeak Type 3 flight call, Canada. Recording by Chris Parrish on Xeno-Canto (click for link).
Evening Grosbeak Type 3 flight call, Sanguenay, Quebec, 5/21/2007. Recording by Chris Parrish on Xeno-Canto (click for link).

The distinctive Type 3 differs from Types 1, 2, and 4 by being slightly longer and lower-pitched and distinctly burry.  Field guides with an eastern focus have often compared the calls of Evening Grosbeak to certain vocalizations of House Sparrow, and Type 3 is the reason why.

Type 4

Range: The southern Rockies (Colorado and New Mexico), occasionally wandering north at least to the vicinity of Jackson Hole, Wyoming.

Flight call:

Evening Grosbeak Type 4 flight calls, Colorado.
Evening Grosbeak Type 4 flight calls, Delta County, CO, 3/9/2008.

The high-pitched and piercing Type 4 flight calls are most similar to Type 2 flight calls, both on the spectrogram and to the ear, but slighty huskier and less clear.  I’m not certain I could tell them apart in the field with confidence, but the two have never yet been recorded in each others’ range to my knowledge.  Here’s another recording of Type 4.

Type 5

Range: The Sierra Madre of Mexico, north to southeastern Arizona.

Flight call: To my knowledge, only one recording of this type has been made, and here it is:

Evening Grosbeak Type 5 flight call, Arizona. Recording by Rich Hoyer (used here with permission).
Evening Grosbeak Type 5 flight call, Cochise County, AZ, 4/14/1999. Recording by Rich Hoyer (used here with permission).

If this recording is typical, then Type 5 is distinctive: even longer and burrier than Type 3, but high-pitched like Types 2 and 4.  If I had to guess, I’d say that the doubled rhythm is probably due to the whim of this individual bird, not characteristic of Type 5 in general, but who knows? — maybe Type 5 is the Mountain Pygmy-Owl of Evening Grosbeaks.  If you have any recordings of Evening Grosbeak from Arizona or Mexico (or you know someone who does), please let me know!

Regions of Mystery

There are some places where we don’t really know which type to expect:

  • Southwest Oregon and northern California: Types 1 and 2 have both been recorded in this region, and the actual limits of their distribution here are poorly known.
  • Black Hills of South Dakota: The one recording I have is of Type 1, but I think Type 3 might also be likely, and Type 4 might wander in.
  • Arizona: My guess would be that Type 4 is most common in the northern and central parts of the state, while Type 5 is the most likely type to be encountered in the southeastern mountains, but we need more data.

You know what that means: more recordings necessary!

What We Don’t Know About Bird Sounds

What We Don’t Know About Bird Sounds

A while back I mentioned my long-standing desire to post a list of things we don’t know about North American bird sounds, with an emphasis on the simple questions that amateur sound recordists could answer.  I’ve finally decided to take a crack at it.

Below, you’ll find my first attempt to list some things we don’t know.  It’s not even close to an exhaustive list, nor is it necessarily up-to-date — it’s merely a teaser, mostly based on a quick perusal of a few select BNA accounts.  My whole purpose is to inspire some amateur research projects. Most of these are questions that amateurs can answer in whole or in part.  You might be surprised at what you could contribute to science with a little time and energy.

Song Repertoire

How many different songs can one male bird sing?  This question can be easily answered by simply recording singing individuals for an extended period. The answer is sometimes quite different even between closely related species, or within populations of a single species.  Here are some birds whose song repertoires are poorly known.

  • Northern Shrike
  • Loggerhead Shrike
  • Mountain Bluebird
  • Virginia’s Warbler
  • Black-and-white Warbler
  • Hepatic Tanager
  • Lark Sparrow
  • Dickcissel
  • Orchard Oriole

Begging Calls

An easy way to contribute is to record the sounds of young birds, either in the nest or out of it.  Ideally, locate a nest and monitor it, noting the dates of hatching and fledging, and making recordings on a regular basis in between, to document the development of the sounds.

  • Mountain Bluebird
  • Lucy’s Warbler
  • Dickcissel
  • Blue Grosbeak
  • Spotted Towhee

Geographic Variation

Birds in this category may sound different in different parts of their range.  Some of these differences may have taxonomic implications.  On the other hand, some of these birds may not sound much different across their ranges; we don’t really know.

  • Cave Swallow
  • Curve-billed Thrasher
  • Spotted Towhee (calls)
  • Great-tailed Grackle

Call Repertoire

The birds in this category may make sounds that do not appear on commercially available bird sound recordings and are poorly described in the scientific literature.  To solve the problem, we need recordings of all the sounds birds make — not just the pretty ones, or the loud ones — plus detailed notes on the behavioral context of the sounds: what was the bird doing when it made the sound?  What time of year and day was it?  What was the bird’s age and sex?  And so forth.

  • Clark’s Grebe
  • Common Moorhen
  • Olive-sided Flycatcher
  • Greater Pewee
  • Loggerhead Shrike
  • Blue Grosbeak
  • Vesper Sparrow
  • American Tree Sparrow (more on this in an upcoming post)
  • Pine Siskin
  • Bullock’s Oriole

Spectrographic Analysis

Many vocalizations have been described in the literature only phonetically, and it can be difficult to determine which call the author was hearing — or which one you are hearing — unless you have spectrograms to compare.  These species could use a formal description of repertoire with spectrograms:

  • Northern Shrike
  • Phainopepla
  • Common Myna
  • Bewick’s Wren (calls)
  • Rock Wren
  • Hepatic Tanager
  • Summer Tanager
  • Lark Sparrow

Flight Calls

Not enough flight calls have been recorded from these species (during the daytime) to determine the limits of variation in the sounds they might make during nocturnal migration.

  • MacGillivray’s Warbler
  • Western Tanager
  • Black-headed Grosbeak
  • Brewer’s Sparrow
  • Western Meadowlark

Other Questions

  • Goldfinches (at least Lawrence’s and Lesser, and probably American also) apparently sing two types of songs: a long, continuous one and a disjointed one that sounds like a long string of calls.  The two song types grade into one another.  The disjointed song has never been described in the literature and its purpose and behavioral context remain unknown.
  • Male Painted Buntings may continue learning new songs after their first year of breeding; extensive recordings of the same individual across multiple years would help resolve the question.
  • The BNA account on Bullock’s Oriole says that “Males seem to sing only a single song,” but I suspect the situation is much more complex, as it is in the closely related Baltimore Oriole.  Shall we find out?

And that, folks, is just what I found in a perusal of roughly 50 BNA accounts.  This is just scratching the surface.  Note how many common and widespread species are on the above lists.  Everybody in North America can contribute if they’ve got the time — and especially if they have recording equipment.

If you’ve got anything to add to this list, post it in a comment!  I’ll try to get a master list put together eventually.

The Alternate Song of Prothonotary Warbler

The Alternate Song of Prothonotary Warbler

Prothonotary Warbler, Chatham-Kent, Ontario, 5/4/2008. Photo by Gavan Watson (Creative Commons 2.0).
Prothonotary Warbler, Chatham-Kent, Ontario, 5/4/2008. Photo by Gavan Watson (Creative Commons 2.0).

They don’t call it the Golden Swamp Warbler anymore, but name would still be apt, because the flame-yellow Prothonotary is a familiar sight in the swampy areas of southeastern North America.  It’s a wonderful and evocative bird, one that even non-birders tend to notice when it perches or sings nearby.  It’s one of the few warblers that nests in cavities, and it is the sole member of the genus Protonotaria.

In 2006, I joined a volunteer team in Cornell’s search for the Ivory-billed Woodpecker in the White River National Wildlife Refuge of Arkansas.  During the two weeks I spent walking around in the untrammeled, uncampephiled wilderness, I had many spectacular close-up encounters with wildlife, but the most amazing was with a male Prothonotary Warbler.  I was standing in hardwoods on the edge of a flooded swamp when the golden bird popped up over the water and began to sing.  I switched on my microphone to record it, and suddenly it flew into a leafless sapling right over my head.  I didn’t dare breath or move; I just kept the microphone running, hoping the bird would stay in the tree, hoping it would sing again.  Sure enough, after a few minutes of foraging it began to belt out its familiar primary song: a fast monotone series of high clear upslurred whistles, not particularly musical, often transcribed as “sweet sweet sweet sweet sweet.”

Prothonotary Warbler primary song, Phillips County, Arkansas, 4/4/2006.
Prothonotary Warbler primary song, Phillips County, Arkansas, 4/4/2006.

But then the bird did something even more extraordinary.  It began to sing another song, one that was so faint that if the bird hadn’t been within five meters of me, I surely wouldn’t have heard it.  And it was like nothing I’d ever heard from a Prothonotary before:

Alternate song of Prothonotary Warbler (same individual as above).
Alternate song of Prothonotary Warbler (same individual as above). Note that the song has three parts in a strict syntax AAAABBBBBBBCCC. The four calls at the end were not part of the song structure; I only heard such calls a few times, usually right before or after a song strophe. They appear to correspond to the typical flight call of the species, as recorded by Evans & O'Brien (2002).

I went to the literature to find out what I had recorded, and discovered this in Lisa J. Petit’s Birds of North America account (emphasis mine):

Second, less frequent song is sung primarily during interactions with females, often in aerial Flight Display. This extended song (Spector 1992) is longer and slightly more complex than primary song, beginning rapidly and slowing down at end: chwee-chwee-chwee- chwee, teer, teer, teer (LJP) or che-wee-che-wee-chee-chee, chee-chee-che-wee-che-wee (Walkinshaw 1979). Brewster (1878) described this song as resembling song of Canary (Serinus canaria), sung quietly, and consisting of “trills or water-notes interspersed.” Roberts (1899) referred to the song as beginning with the “usual rapid monotone” and ending with a “varied warble.” No sonograms of this song are known to exist.

“No sonograms known to exist,” of course, is the same thing as saying “no recordings known to exist.”  Well, we fixed that, didn’t we?

Or did we?  Upon reflection, the quote above demonstrates some of the difficulties inherent in trying to match old voice descriptions with modern recordings.  Is this really the “alternate” song of males?  After all, no female was present, and the bird wasn’t singing in flight.  Could it be some other type of song?  In her account, Petit also mentions two other potential candidate vocalizations, apparent juvenile subsong and female song:

Two separate observations by LJP during Jul 1985 of immature birds (sexes unknown, both in femalelike plumage-one color-banded, 45 d old; the other unbanded, assumed immature on basis of behavioral interactions with adult pair) singing quiet, raspy, oriolelike warble that did not resemble primary song of adults. Songs were 2-3 s long and were repeated 3-4 times. In Jun 1987, an unbanded female (apparently adult, since it was building nest) was heard to give same type of song, repeated 3 times.

I’m not sure how female song fits into the picture, or whether some of the observers cited in the first quote might have been describing it, but one thing is clear: What I recorded was not subsong.  Subsong is given by juvenile birds between fall and spring as they practice for their big debut on a breeding territory.  It’s poorly structured, with individual notes randomly mixed and rarely repeated, or repeated in garbled form.  The song I recorded, on the other hand, was crystallized: the bird repeated it more than a dozen times, and each time it followed the exact same syntax pattern, with small variations in the exact number of notes A, B, and C, but absolutely no variation in their order, fine structure, or rate of delivery.

Many warblers have complex alternate songs.  Some better-known examples include the “flight songs” of Ovenbird and Common Yellowthroat (for the latter, listen here, between the 21 and 24 second marks).  Paul Driver’s got a neat recording of the extended song of Worm-eating Warbler, and Andrew Spencer has posted to Xeno-Canto what may be an alternate song of Black-and-White Warbler, although it may also be a type of call.  Many of these song types are rarely heard and even more rarely recorded, so I’d love to hear of more examples.

Given that Prothonotary Warbler has attracted a good deal of research attention over the years, I would be surprised if nobody else had recorded the alternate song by now.  If you have any information to share, please let me know.  It’s probably worth writing up a note for publication in a journal.

The Crossbill Quiz: Answers

The Crossbill Quiz: Answers

Here are the answers to the quiz from the last post:

a. Type 4

Type 4 is believed to specialize on the cones of Douglas-fir.   It is widespread but somewhat irregular in its distribution: it is usually common in moist forests of the Pacific Northwest and can be frequently found in dry forests there also.  It is regular in southeast Arizona, and indeed this particular recording was made at Barfoot Junction in the Chiricahuas in May 2009.  It appear to be absent some years from Colorado, but fairly common in other years; 2009 saw a decent influx of this type into the state.

Ken Irwin (unpubl.) has proposed that hidden inside Type 4 there is another call type,  Type 10, that specializes on sitka spruce in coastal California.  It’s still unclear to me whether Type 10 is a separate call type or just a variation on Type 4.  Whatever the case, Type 10 seems to wander widely, at least across the northern states, out to New England and Maryland.

The Type 4/10 group, as a whole, sounds very distinctive because of its upslurred calls.  It may be a little hard to hear that they are upslurred because they are delivered so fast, but the rising, flicking quality of the calls is pretty distinctive, reminding some people of the “whit” calls of Empidonax flycatchers.

b. Type 9, the South Hills Crossbill

This type is sedentary and restricted to the South Hills and Albion Mountains of Idaho, where it feeds on the local variety of lodgepole pine.  It sounds kind of like Type 2, clear, simple, and downslurred, but it is noticeably low-pitched.  I think it is kind of “dull-sounding,” without much ring or resonance, but I’d be interested to hear how other people describe the difference.  I recorded this in the South Hills in September 2009.

c. Type 2

Here’s a Type 2.  This is probably the most numerous crossbill in North America; it is common almost everywhere Red Crossbills can be found.  It is surmised to specialize on ponderosa pines.  Across its range its calls are variable, but the high-pitched, clear, downslurred quality is fairly distinctive.  This recording was made in Boulder County, Colorado, in July 2007.

d. Type 3

This is one of the smallest crossbills (only Irwin’s proposed Type 10 is similarly small) and is one of the most common crossbill types in moist northwestern forests, apparently specializing on western hemlock.  It also can be found across the boreal forest, occasionally into New England, and it wanders rarely into the southern Rockies — there are now two certain records for Colorado and more in the “probable” category.  There are also recordings from Arizona.

Types 3 and 5 sound similar to my ear: they are more complex than the types we heard above, less clear and less obviously upslurred or downslurred.  Type 3 is the duller-sounding of the two, but I must admit I need practice with this identification.  This particular recording, the second-ever for Colorado (from the Grand Mesa, February 2009), was made by Andrew Spencer when I was right beside him–and I didn’t turn on my microphone because I thought they were “just” Type 5s.  To be fair, Andrew recorded them because he thought they were White-winged Crossbills.  🙂  He didn’t identify them until days later when he looked at the spectrogram.

e. Type 5

This is the “other” common crossbill in Colorado (besides Type 2), a widespread bird of high elevations in the West, apparently adapted to feed on lodgepole pine but also very fond of Engelmann spruce.  In direct comparison I think it sounds more “metallic” than Type 3, but it’s a tough call in the field.  A distant flock can sound a lot like a bunch of crickets.  This recording was made in Larimer County, Colorado, in June 2009.

The Crossbill Quiz

The Crossbill Quiz

Last week I facilitated the Sound Identification Panel at the Western Field Ornithologists Conference, which is a wonderful privilege I have been treated to for each of the last four years.  For those who don’t know, the Sound ID Panel is an annual WFO tradition started by Sylvia Gallagher. In front of a large live audience, a moderator (that’s me) quizzes an expert panel on the identification of mystery bird sounds.  This year our panelists were Ted Floyd, Oscar Johnson, Jon Feenstra, Rich Hoyer, and Tayler Brooks, and I must say they did an outstanding job.  In collaboration with each other, and notwithstanding the occasional wrong answer, they managed to identify almost every mystery sound in the end, and believe me, that’s not an easy feat.

In 2009 I decided to cross a line I’ve been reluctant to cross in the past.  I put Red Crossbills in the mix.  It seemed natural, since the conference was in Idaho, home to the endemic South Hills Crossbill, and our keynote speaker was crossbill guru Craig Benkman.  I gave the panel the following quiz:

Red Crossbill Call Types: Matching

In this quiz you’ll hear one example of each of the four most common and widespread crossbill types in the western United States, listed below with the tree species they are believed to specialize on:

  • Type 2 (Ponderosa Pine)
  • Type 3 (Western Hemlock)
  • Type 4 (Douglas-Fir)
  • Type 5 (Lodgepole Pine, Rocky Mountain variety)

Plus, given the location of the conference, we’re tossing in the sedentary and range-restricted South Hills Crossbill, endemic to Idaho, which has been proposed as a separate species, Loxia sinesciuris:

  • Type 9 (Lodgepole Pine, South Hills variety)

Here are the sound clips in random order.

a.

b.

c.

d.

e.

How well can you do?  Answers will be posted in a subsequent message.

New Listserv Alert

New Listserv Alert

Last spring Chris Tessaglia-Hymes of Cornell University started a listserv devoted to the discussion of nocturnal migration.  Here’s how Chris described it in his inital post:

The primary purpose of the List is to provide an effective electronic forum for experienced birders to discuss the identification of night flight calls of migratory birds, exchange ideas about recording equipment design and setup, disseminate information about active or predicted night flights in your area, and to better understand weather and RADAR data as they relate to patterns of nocturnal bird migration.

The listserv started off slow, but it has slowly gained participants (including, just recently, yours truly), and now that the southbound nocturnal migration is in full swing across North America, the postings are really picking up.  You can monitor the discussion at the online archive.  To join the list, you can email Chris to request that he add you, or you can check out the Welcome and Configuration page.  Either way, this is a great opportunity to join (or just to listen in on) the national conversation about nocturnal flight calls!

The Fall Challenge

The Fall Challenge

I’ve noticed that an awful lot of nature sound recordists in North America have traditionally focused on recording in the spring and early summer.  If you browse the Macaulay Library catalog, or the Borror Lab‘s recordings, or Xeno-Canto‘s North American collection, you’ll see exactly what I mean.  The vast majority of recordings are made from April to June, with a fair number from March and July as well.  Late winter (January-February) is an underrepresented period, but it pales in comparison to the period from August to December, when it seems like almost nobody goes out with a microphone.

We’re heading into that traditional “dead period” now, and I just want to point out that no matter where you live, there are some terrific opportunities for recording (and listening to)  some of the most interesting and worthwhile bird sounds of the entire year!  For example:

  1. Begging calls, begging calls, begging calls. I said it thrice because I believe it’s one of the most shamefully neglected classes of bird vocalization, and the Fledgling Project agrees with me.  You won’t have to browse many Birds of North America “Sounds” accounts before finding the phrase, “development not described.”  That’s because not enough microphones have been pointed at squalling baby birds, whether in or out of the nest.  This is one of the easiest ways for an amateur recordist to make a big contribution to our knowledge of birds.
  2. Juvenile subsong. In many species of bird, youngsters have already started to practice their songs, in a developmental process akin to the “babbling” of human babies.  The results can be fascinating, beautiful, and scientifically significant.
  3. Shorebird calls. Millions of shorebirds are headed south right now throughout North America, and some of them will still be southbound as late as October.  Shorebirds are traditionally pretty poorly represented in audio collections, but there is a lot to learn about their calls also.
  4. Fall song. Some birds can occasionally sing as much on fall migration as they do on spring migration, or even more, with vireos being a great example.  Phoebes and other flycatchers can occasionally give variable renditions in fall of their typically stereotyped spring songs.  How and why does fall singing differ from  spring singing?  More recordings would help answer the question.
  5. Nocturnal flight calls of fall migrants. Many people have jumped on this bandwagon in the East in recent years, and some are starting to do so in the West — in fact, in just two weeks I’ll be co-leading a workshop on nocturnal migration here in Colorado that filled up some time ago.  I know people in several states who have just begun putting microphones out to capture the sounds of the overnight flight, and there are a lot of online resources to help people get involved.  Start with Oldbird.org, the website of Bill Evans*, one of the original flight call gurus, where you can listen to flight calls online and learn how to build your own cheap nocturnal sky microphone. You can hear more flight calls from the East on the websites of Steve Kelling., A.P. Martin, and Matt Orsie,  and get updates on western nocturnal migration by following Ted Floyd on Twitter.
  6. Winter specialties. Crossbills, juncos, American Tree Sparrows, Evening Grosbeaks, redpolls, longspurs, Snow Buntings, swans, geese, gulls, ducks.  And crossbills.  Need I say more?

If you already record sounds, don’t leave your microphone at home in the bottom half of the year!  Recordings from fall and winter are rarer, and therefore more valuable.  And if you don’t yet record, but have the wherewithal to start, now’s a great time!

*revision 8/18/2009: thanks to Ted Floyd for pointing out to me that Oldbird.org is Bill Evans’s website, not Michael O’Brien’s.