Identification – Page 8

Splitting the Gray Hawk

25 July 2009 Nathan Pieplow

buteo_plagiatus — Gray Hawk, B. plagiatus, Belize, 2005. Photo: The Lilac-breasted Roller (Creative Commons Attribution 2.0).

The Gray Hawk, whose scientific name recently changed from Asturina nitida to Buteo nitidus (AOU 2006), was historically considered two species:

Gray Hawk (Asturina plagiata or Buteo plagiatus), comprising a single subspecies found from the southern United States south to northwestern Costa Rica;
Gray-lined Hawk (Asturina nitida or Buteo nitidus), including races costaricensis, nitida[-us] and pallida[-us], ranging from southwestern Costa Rica south through much of South America to northern Argentina.

In recent years the AOU has recognized only a single species, with a range from Arizona all the way to Argentina, but evidence is mounting that it should in fact recognize two. The BNA account (Bibles et al. 2002, subscription required) mentions many well-established differences between the two groups in both plumage and measurements, which led B. A. Millsap to propose a split in his 1986 master’s thesis (abstract). Then, in 2003, Riesing et al. published a molecular phylogeny of the genus Buteo which not only found that Asturina was embedded within Buteo (resulting in the aforementioned change of genus) but also found evidence for a species split:

Substantial variability was detected within B. nitidus. The subspecies B. n. plagiatus is 9% apart from B. n. nitidus and B. jamaicensis costaricensis, respectively. Thus, the earlier proposed species status of plagiatus (Millsap, 1989) is supported by our data.

The American Ornithologists’ Union Checklist Committee, however, wasn’t convinced:

Riesing et al. (2003) suggested that the groups should be recognized as distinct species, but did not provide supporting data.

I’m no molecular biologist, so I can’t comment in depth on the quality of the data or the analysis, but I can say that Riesling et al. had a pretty small sample size: only a single sample each of the Gray Hawk subspecies nitidus, costaricensis, and plagiatus. And although they looked at two genetic markers overall, only one marker seems to have been sampled from all three taxa. In that one genetic marker, however, the samples of “Gray” and “Gray-lined” Hawks were as different from each other as the northern “Gray” Hawk is from Red-tailed Hawk, which is a substantial difference indeed.

Here is added evidence for the split: the plagiatus group and the nitidus group differ substantially in vocalizations, a fact that seems to have gone unreported in the literature so far. (Wikipedia says the vocalizations of both groups are identical, but does not cite this information.) In this post we’ll start simple:

One-note (alarm) call

The most commonly heard vocalization of both species is the single-noted call, which apparently indicates alarm, at least in the plagiatus group. The single-noted call appears to be fairly stereotyped within populations, but strikingly different between them:

Alarm call of Gray Hawk (Buteo plagiatus), Guadalupe Canyon, AZ, 5/16/2009 (14-20).

Alarm call of Gray-lined Hawk (Buteo nitidus), Rio Caura south of Maripa, Bolivar, Venezuela, 1/4/2007 (03-07).

The following differences can be used to separate the two calls consistently:

Duration. The call of the Gray Hawk lasts 1.5 – 2.0 sec, while the call of the Gray-lined Hawk is typically 0.5 – 1.0 sec long.
Frequency. The call of the Gray-lined Hawk is significantly higher-pitched, with a maximum frequency of ca. 3.5 kHz, versus a maximum of less than 2.5 kHz for Gray Hawk.
Energy spectrum. In the call of the Gray-lined Hawk, the energy is overwhelmingly concentrated in the fundamental, giving the call a clearer, more piercing tone quality, while in the call of the Gray Hawk, it’s the first harmonic that is strongest, with comparatively more energy in the second harmonic as well, relative to the fundamental. This gives the call of the Gray Hawk a distinctly more nasal tone quality.
Pattern of inflection. The shape of the two calls on the spectrogram is consistently different. The Gray Hawk’s call is always a smooth overslur with a very early, very brief peak, with the final 75% of the call comprised of a long, nearly monotone “tail.” The Gray-lined Hawk, meanwhile, always shows a much more evenly overslurred shape, with a “flat-topped” look and a shorter and more sharply downslurred “tail.” In addition, the Gray-lined Hawk almost always has a “break” in its voice, a point in the terminal downslur at which the pitch drops almost instantaneously. In the above example this occurs almost exactly at the 1.5 sec mark.

On this page you will find comparative spectrograms from Xeno-Canto, with (as of this writing) 13 examples of Gray-lined Hawk’s alarm call and 2 examples of Gray Hawk’s. Xeno-Canto’s one recording from Panama, apparently the only representative of the Gray-lined subspecies costaricensis, seems odd, so a little more digging is in order there. Other than that, however, the distinctions I noted above hold in all cases, and I don’t note any systematic differences between subspecies nitidus and pallidus.

I’d like to revisit this issue in a future post, to investigate possible differences in the series call and to bring in results from the Macaulay Library‘s website, which appears to be under the weather at the moment. Stay tuned.

Pygmy-Owl vs. Chipmunk

16 July 2009 Nathan Pieplow

In addition to the comments on my recent pygmy-owl post, I got five private emails, all of which also implicated Merriam’s Chipmunk as the likely source of the pygmy-owl-like sound. I emailed Doug Von Gausig, and he was very amenable to the possibility that he might have recorded a chipmunk instead of a pygmy-owl. I think this is likely the case.

The best evidence came from a 1976 paper by Leonard Brand in the journal Animal Behaviour: “The vocal repertoire of chipmunks (Genus Eutamias) in California” (email me for a PDF copy). In addition to the “chip” calls that are the most common form of alarm note in all ten chipmunk species in California, Brand mentions a “chuck” call that matches our mystery sound:

Chucks were lower pitched than chips, with their fundamental frequency between 0.5 and 2.0 kHz. Their lowest frequencies were at the beginning and end, with higher frequencies in the middle of the syllable. Eutamias townsendii chucks had from zero to five harmonics at approximately 2 kHz intervals. Each chuck was from 0.03 to 0.05 sec long. Chucks were given by all species, and they all had a form similar to E. townsendii [emphasis mine]. Chucks were usually given…in a steady series, from 50 to 178 per min.

The description is a pretty good match for the pygmy-owl-like sound, but I think the real clincher is Brand’s spectrogram of the “chuck” call:


"Chuck" call of Townsend's Chipmunk (Tamias townsendii), adapted from Brand (1976), Fig. 5.	Probable "chuck" call of Merriam's Chipmunk (T. merriami, Chews Ridge, Monterey County, CA, 1/12/2009. Recording by Andrew Spencer.

I fiddled with the axes on the spectrogram of Andrew’s recording to make the two as comparable as possible, and although there are slight differences, the similarities are striking, right down to the faint third voice in between the fundamental and the first harmonic.

Brand was using a Kay Electric Company spectrograph machine on the wide-band setting, which explains the much thicker lines on his spectrogram. Although I’m not a fan of the wide-band setting, I do have to applaud Brand for resisting the temptation to trace his spectrograms, as was the rage in the 1970s. Thank goodness we have computers to do the dirty work for us these days!

Overall, I see no reason not to identify Andrew’s recording as the “chuck” call of a chipmunk, which would make it a Merriam’s Chipmunk (Tamias merriami), the only species in Monterey County. Here’s another link to the sound:

I still marvel at the uncanny resemblance to an owl!

Macaulay’s Red Crossbill Types

14 July 2009 Nathan Pieplow

By popular demand, here’s a natural extension of my first post: an index to the Red Crossbill call types on some of the cuts in the Macaulay Library collection. First, a couple of introductory notes and caveats:

Typing Red Crossbills from recordings is not an exact science. It’s not difficult if the bird is giving actual flight calls, but if the bird is singing, things can get confusing in a hurry, because the songs of Red Crossbills frequently contain strings of repeated sounds that resemble flight calls, but are really just notes in the song. These song notes might be variations on the bird’s own flight call type, or they might somewhat resemble another flight call type, or they might just be something else entirely. The point is that a solid identification to type requires a good string of call notes outside the context of song — and not all recordings provide such.
In addition to song and flight calls, crossbills also give other calls, most notably the excitement calls (or “toops”) and the juvenile begging calls (or “chittoos”). The excitement calls do vary from type to type. It is not known whether the begging calls do too. To avoid confusion, I’ve limited the examples in this post to cuts of flight calls only.

All identifications to type have been corroborated by Matt Young at Cornell. Thanks for your help, Matt!

Type 1

#138304	New York	8/6/06
#138305	New York	8/6/06
#138306	New York	8/6/06
#138312	New York	8/6/06
#138320	New York	8/6/06
#138323	New York	8/6/06

Type 2

#39869	Oregon	9/4/85
#44960	Oregon	6/18/89
#48897	California	6/13/90
#49601	California	6/13/90
#84567	California	6/10/97
#99362	California	6/4/92
#111103	Oregon	4/20/90
#111104	Oregon	4/20/90
#119400	California	5/29/01
#120416	California	6/5/02
#120423	California	6/7/02

Type 3

#94205

Maryland

12/28/1997

(with Type 10)

Type 4

#58167

Alberta

5/23/61

Type 10

Groth’s (1993) monograph identified eight Red Crossbill types in North America. Benkman (1999) identified a ninth type endemic to the South Hills of Idaho. Ken Irwin (unpubl.) has proposed that there is a tenth type, which was actually recorded by Groth, but lumped with Type 4. Ironically, my Colorado Birds article mentions this call type as a variant of Type 4 (the variant without the initial downslur). Right now, expert opinions vary somewhat on whether this variant is actually separate from Type 4, but whatever it is, it seems to be relatively common and widespread, or at least widely wandering.

#94201	Maryland	12/28/97
#94205	Maryland	12/28/97	(with Type 3)
#112167	Maine	7/16/98
#130478	New York	5/17/98

I hope this post is helpful to those who want to try to sort these types out for themselves. In conjunction with the Red Crossbill cuts on Xeno-Canto, the Macaulay cuts should get you off to a good start!

Pygmy-Owl Confusion

11 July 2009 Nathan Pieplow

On 12 January 2009, my friend Andrew Spencer recorded an unseen creature on Chews Ridge in Monterey County, California:

Chews Ridge, Monterey County, CA, 1/12/2009. Recording by Andrew Spencer

To my ear this sounds like a Northern Pygmy-Owl (sensu stricto: Glaucidium gnoma californicum), and the spectrogram shows many of the characteristics of that species. The note shape is pretty classic, with a sharp initial upslur and terminal downslur, and an overall barely downslurred trend to the rest of the note. Almost all of the energy is concentrated in the fundamental, but a couple of faint harmonics are visible, which is standard for pygmy-owls.

But a few things about this recording are strange:

The notes are quite short, about half the length of the average Northern Pygmy-Owl note;
The rate of the series is quite fast (on average about 1 note every 0.66 sec), which is more than twice as fast as you’d expect from pygmy-owls from California;
The pitch of the notes is just a little high, about 1.5 kHz, while most Northern Pygmy-Owl notes fall just above 1.0 kHz;
Oddly, Andrew reports that the sound was coming not from a tree or bush, but from somewhere on the ground. It’s unlikely that Andrew misjudged the origin of the call: he was aiming at it with a parabolic dish, and if the source of the sound hadn’t been close to the focus of the parabola, most likely the harmonic would be absent from the spectrogram and the echo would be louder in relation to the original sound.

Because the sound came from the ground, Andrew surmised that he might have recorded some kind of mammal. But what kind of mammal could sound so remarkably similar to a pygmy-owl? If there is a mammal in California that sounds like this, then I want to know about it.

I did manage to find a recording that matched Andrew’s: Doug Von Gausig made this recording in almost the same place: along the Carmel Valley Road just east of Carmel, California, on 24 March 1999. In an email, Doug told me his pygmy-owl was unseen, but positioned high within the trees in a dense gallery forest.

The bird on Doug’s recording is even higher-pitched and faster than the one on Andrew’s. Together, these two recordings represent quite a departure from what I’ve come to think of as the “typical” song of californicum. Xeno-Canto, the Macaulay Library and the Borror Lab, between them, have nine recordings of the primary song of Northern Pygmy-Owl, from California, Oregon, Montana, Colorado and Utah. None of the birds in these recordings quite match the Spencer/Von Gausig birds in note length or pitch, and most strikingly, none of them come close in rate: the Borror bird from Utah and Jason Beason’s Colorado bird average about one note every 1.5 sec, while the rest, including the Montana bird, average a note every 2.0 sec or more. At the moment, I’m still a little skeptical that “interior” Northern Pygmy-Owls sing significantly faster than “coastal” Northern Pygmy-Owls on average, but I have long agreed that “Mountain” Pygmy-Owls (Glaucidium gnoma gnoma), which breed from southern Arizona south through Mexico, sing very differently from californicum and probably deserve species status. Here’s their standard song:

"Mountain" Pygmy-Owl (Glaucidium gnoma gnoma), Big Bend National Park, TX, 3/28/2008.

In addition to the typical song with the irregular rhythm, “Mountain” Pygmy-Owls apparently sometimes give a faster, stricter song that is very similar to the song of the Northern Saw-Whet Owl (so similar, in fact, that I suspect the two may represent a vastly underrated ID problem). See the Xeno-Canto forum discussions (here and here) of Allen Chartier’s seven cuts of fast Mountain Pygmy-Owl song from Oaxaca. I was particularly struck by Rich Hoyer’s understanding of a stepwise slowing trend in pygmy-owl song rates as you move counterclockwise from Mexico to Colorado to California to Baja California Sur. Up to a point, that jives with the information I have, but what to make of the two birds from Monterey County that sing at a rate of about 80 notes/minute? Are they representatives of an anomalous local dialect? Or of a different type of vocalization than the primary song? Are they not even pygmy-owls at all?

What gives?

Beware the Bendire’s

10 June 2009 Nathan Pieplow

In the middle of the afternoon a few weeks ago I was sitting in the public library in Sierra Vista, Arizona–a wonderful facility, by the way–escaping the heat of the day to download my bird sound recordings, recharge my batteries, and check my email, when my attention was drawn to a bird hopping directly toward me on the ground. No, it wasn’t in the library–it was on the other side of the floor-to-ceiling plate-glass windows, out in the desert garden. But it might as well have been in the library, because it ended up hopping right up to the window, less than four feet from my face, so that even without binoculars I could clearly see its pale yellow eye, its short, almost straight bill, its nearly-unmarked breast with a few spots front and center…in short, every field mark necessary to confirm its identity as a Bendire’s Thrasher–a scarce species I had seen only three times before.

And then, through the window, I heard it begin to call: a slightly noisy, one-syllabled note reminiscent of the “cheep” call of the American Robin. Naturally, I raced right out to record it:

The call note clinched the ID. It was completely different from the characteristic call of the very similar-looking Curve-billed Thrasher, the loud wit-weet! that is a trademark sound of the southwestern deserts:

Curve-billed Thrasher call. Catalina State Park, Arizona, 2/23/2008 (08-19).

I was particularly excited to record the Bendire’s because their one-syllabled call note had been described in the literature, but as far as I could tell, never recorded — I didn’t know of any commercially available recordings that included it, nor had I ever seen published spectrograms of it. The Macaulay Library didn’t have it, and in the two different mornings I’d spent recording Bendire’s Thrasher in Arizona and California, I’d never even heard it, much less caught it on tape. So I was pretty stoked.

I relayed the details of my sighting to my friend Andrew Spencer, who was due to arrive in southeast Arizona shortly after I returned to Colorado. He was equally excited about this rare recording opportunity, and he made a point of stopping at the Sierra Vista Public Library as well. That morning I got a message from him that relayed some good news and some bad news. The good news: he’d found the bird right where I said it would be, acting just as I’d said it would, giving calls just like the ones I’d recorded. The bad news? It had been accompanied by, and fed by, two adult Curve-billed Thrashers. It wasn’t a Bendire’s at all–it was just a juvenile Curve-billed.

Sure enough, when I went to look at the Bendire’s Thrasher chapter in Kenn Kaufmann’s Advanced Birding, there was the description of a juvenile Curve-billed Thrasher, matching my bird to a T. I had forgotten that Bendire’s has a pale base to the lower mandible, which my bird had lacked. And Kaufmann even mentions the single-syllabled call note of the juvenile Curve-billed. Blast.

The morals of this story:

Juvenile Curve-billed Thrashers look and sound far more like Bendire’s than I ever thought possible;
Even the most seemingly slam-dunk IDs can be wrong;
I still don’t know of a recording of the call of Bendire’s Thrasher. Anyone? Anyone?

Meadowlark “bzerts”: identifiable?

7 June 2009 Nathan Pieplow

I wanted to follow up on my last ID post with an exploration of call notes in Lilian’s and Eastern Meadowlarks. Since meadowlarks learn their songs but not their calls (i.e., their calls are genetically determined), in theory, any significant differences between their calls might provide evidence that they should be split at the species level. Cassell (2002) didn’t analyze calls; the Birds of North America account claims that Lilian’s and Eastern calls are similar. And indeed they are–but there might be some perceptible differences too, as we shall see.

Caveats will abound in this post, and here’s the first one: meadowlark calls appear to be variable both geographically and within individuals. All meadowlarks make a number of different sounds, and some of those sounds grade into one another occasionally. Thus, I’m not certain that all of the sounds I’ve grouped together necessarily belong together in a biological sense–but they do sound similar.

I want to look at a number of different kinds of calls eventually, but today I’ll have time for only one: the bzert.

Bzert

Here are four similar calls from Lilian’s Meadowlark, from four different individuals:

And four similar calls from Eastern, also from four different individuals:

Eastern Meadowlark "bzert" calls. First, second and fourth from Osage County, OK, March 2006 and 2008 (10-66, 06-04, 10-30); third from Larimer County, CO, 5/31/2007 (21-02).

I think I both hear and see a difference there, don’t you? Lilian’s tends to be briefer, more clipped, while Eastern seems to be more drawn-out. If I was confident the above samples were representative of the population as a whole, I’d go ahead and declare these taxa identifiable by call. Unfortunately, some of the recordings in the Macaulay Library complicate the picture. The Lilian’s bzerts on Catalog #56852 are similar to the ones I’ve posted, but those on #20853 and #174 are a little longer. Macaulay’s Eastern bzerts, meanwhile, are all over the map. Catalog #12680 has a number of different-sounding versions of the call, including both upslurred and downslurred versions. #105634 has a number of short ones, much like the Lilian’s I posted. #12699 features several renditions of a bizarre two-syllabled version. Go check these out.

In short, the differences in the samples I’ve posted are tantalizing, but I’m not sure how much to trust them. Larger sample sizes, particularly of Lilian’s, would be helpful in sorting all this out. A systematic and statistical analysis is probably called for in the long run, but in the meantime, listen carefully to your local meadowlarks and make some recordings if you have the wherewithal. One thing is clear: any differences between the bzert calls of these two taxa is pretty slight overall. They are closely related organisms, for sure.

“Lilian’s” Meadowlark songs

2 June 2009 Nathan Pieplow

Introduction: The Literature

Interest in “Lilian’s” Meadowlark has spiked with the publication of Barker et al. (2008), which found significant genetic differences between Lilian’s and other “Eastern” Meadowlarks and recommended that Lilian’s be elevated to species status. Naturally, I keyed right in on the following quote:

Cassell (2002) found significant differences in the songs of Eastern and Lilian’s meadowlarks. However, given the learned nature of song in this group (Lanyon 1957), and the sharing of unlearned call notes between these forms (Lanyon 1957, 1962), the relevance of this observation with regard to species limits remains an open question.

A couple of months back I ordered Cassell’s (2002) thesis through interlibrary loan, to judge the evidence for myself. Overall, I found some aspects of the work very useful, but other aspects quite questionable. In particular, I have two complaints:

In the introduction, Cassell makes the argument that differences in song, as an important isolating mechanism, are important to species boundaries. This is certainly true, but she makes the claim about meadowlarks and then supports it with discussion of nightjars, manakins and antbirds, none of which learn their songs. Meadowlarks not only learn their songs, but individuals have complex repertoires and populations show geographic dialectal differences. In addition, where their ranges overlap, Eastern and Western Meadowlarks defend territories against one another and will respond to playback of one another’s songs. Thus, on the one hand, the two species of meadowlarks recognize each other’s songs as similar enough to pose a territorial threat, a threat usually only posed by conspecifics. On the other hand, the two meadowlarks very rarely interbreed, and hybrids are infertile, so some kind of strong isolating mechanisms are clearly at work. The ways in which meadowlarks recognize songs must be much more complex than a simple evaluation of “same” or “different,” and so in my opinion the role that song plays in isolating these taxa needs more study.
Cassell groups songs by number of “syllables” (2, 3, 4 or 5). She then compares, e.g., all two-syllabled songs of Lilian’s to all two-syllabled songs of Eastern. She doesn’t justify this methodology, and it seems to me that it makes an unwarranted assumption that all same-syllabled songs are homologous (that is, that songtypes with the same number of syllables share a closer evolutionary history with each other than with songtypes of a different number of syllables). To her credit, Cassell does cover her bases a little bit by adding a different analysis, comparing all long syllables (>0.20 sec) to all short syllables (<0.20 sec). But here again is a questionable assumption of homology. I would have found the whole argument more convincing if she had performed her analysis on the level of the whole song rather than the syllable.

Despite these issues, Cassell does convince me that Lilian’s songs average significantly lower in frequency than Eastern songs, in agreement with the descriptions in Sibley’s field guide. Cassell says:

In the field, the astute listener may recognize the primary song of S. m. lilianae by its overall lower pitch than that of S. m. magna.

So far, my experience indicates that this statement holds true in most (but not all) cases. Lilian’s song is frequently, but not always, low-pitched enough that it sounds like Western Meadowlark in tone quality (although the pattern of each song is still much more like Eastern than Western). In addition, it seems to me that Eastern Meadowlarks frequently end on a drawn-out, nearly monotone clear whistle, while Lilian’s tend to end on a whistle that is much more downslurred. There is a lot of overlap in the final note type, so caution is warranted, but I think the combination of terminal inflection and, especially, overall pitch (perceived largely as tone quality) should identify most Lilian’s Meadowlark songs.

Let’s Test This Hypothesis

A few weeks ago in Arizona I was able to record a few Lilian’s Meadowlark songs:

limes3str — Lilian's Meadowlark songs, Willcox, AZ, 5/17/2009 (15-17, 15-18, 15-13)

The first songtype, with its low pitch and its complex middle section, is particularly reminiscent of Western Meadowlark, but all three above seem fairly typical of Lilian’s. Note the downslurred endings.

For comparison, here are three typical songs of Eastern Meadowlark. Note the more “ringing” monotone endings (characterized by more horizontal lines on the spectrogram) and the relatively high pitch (lowest frequencies about 3 kHz, as opposed to 2 kHz for Lilian’s):

Eastern Meadowlark songs. (A) Larimer County, CO, 6/24/2005 (5-51); (B) Larimer County, CO, 5/31/2007 (21-10); (C) Osage County, OK, 3/21/2008 (10-33)

If all songs of both forms fit these patterns, field identification would be pretty easy, but sometimes the birds will throw you for a loop. Here’s a Lilian’s that sounds more like an Eastern on account of its high pitch and monotone ending:

Lilian's Meadowlark song. Kansas Settlement, AZ, 5/14/2009 (13-34).

And here’s a Eastern that sounds something like a Lilian’s on account of its relatively low pitch:

Eastern Meadowlark song. Larimer County, CO, 6/24/2005 (5-52).

And, of course, not all Easterns have the ringing monotone ending:

Eastern Meadowlark song. Larimer County, CO, 5/31/2007 (21-10b).

For a little more ear practice, check out this wonderful repertoire remix of 19 different Lilian’s Meadowlark songtypes, all recorded by Andrew Spencer on 6/1/2009 from one individual bird in Eddy County, New Mexico. You’ll notice that about half the songtypes end in a ringing monotone whistle, which seems to be a slightly higher percentage than among the birds I recorded in Arizona.

To hear more Eastern Meadowlarks, check out Xeno-Canto’s collection. The Macaulay Library has plenty of Eastern Meadowlark songs also, and even a few Lilian’s.

Pop Quiz

All right, let’s find out how well this works. Here’s a remix of three meadowlark songs. Which ones are Eastern and which are Lilian’s? Leave your guesses in the comments field, and I’ll post the answers in a couple of days.

Getting started with crossbills

30 May 2009 Nathan Pieplow

I think most birders know by now that Red Crossbills in North America sort into a number of different call types, each of which may constitute a cryptic species. Identifying these types in the field promises to be a bugaboo of legendary proportions. Where does one begin?

In this post I’ve collected links to some online resources that can get you started: a sort of Crossbill Q & A, if you will.

1) What are the crossbill types? How did they evolve? Are they for real?

A great source for beginning to answer these questions is Craig Benkman’s introduction to crossbill types in the July 2007 issue of Colorado Birds. Although it doesn’t discuss identification, the article’s overview of the research on crossbills is extremely valuable to anyone in North America, in spite of its nominal focus on Colorado.

When you’re ready to dig a little deeper, head to Benkman’s home page and look at the list of publications he has posted in PDF form. The man is a scholarly publication machine. Every important paper on crossbill types that has been published to date can either be downloaded from Benkman’s page or can be found referenced in the bibliographies of one or more of his works.

2) Where can I listen to online recordings of Red Crossbill types?

Your first stop should be Jeff Groth’s old page on the website of the American Museum of Natural History. Although Benkman may be the current guru, Groth was the original discoverer of the call types. The good news is that his page has audio files of the flight calls, excitement calls (“toops”), and alarm calls of types 1-7. This makes it the most comprehensive collection of crossbill vocalizations on the web. It also has range maps and basic natural history information for each of these types.

The bad news is that Groth’s site was, believe it or not, last updated in 1996, back when the Internet was in primary school. Not all of the links still work. There’s only a single audio file for each vocalization, and worst of all, because the files date from those dark days when 50 kB took a long time to download, they’ve been cut so short that they don’t sound like they do in the field–instead they all sound too much like each other. Appreciate Groth’s site for what it has, but don’t let it intimidate you. Crossbill identification is very hard, but it’s not hopeless.

Here are a couple of less comprehensive but more user-friendly resources:

Matt Young’s crossbill identification paper on the eBird website. This is the best identification article published to date. It deals only with Red Crossbill types 1-4 (flight calls only) and White-winged Crossbill (which, interestingly, does not have multiple populations defined by call type). These are the birds you are most likely to encounter if you live in the eastern United States. If you live in the West, you are most likely to encounter Red Crossbill types 2-5, so this article will still be of great use to you. It has much higher-quality (i.e. longer) recordings than Groth, including scrolling spectrograms in .mov format. However, it has only a single example of each type, which makes it more difficult to get an idea of the variation within types.
My Colorado Birds article on types 2, 4, and 5 in Colorado. This was published along with Benkman’s overview in July 2007, and already I’m a little ashamed of the poor quality of some of the accompanying recordings (which you can listen to here: Fig. 1a, 1b, 1c, 2a, 2b, 2c). Several people have pointed out that my spectrograms should have been zoomed in a little more, too. Sorry about that. On the bright side, this piece is a good supplement to Matt’s article, especially because it discusses Type 5, which is widespread in the West.
Xeno-Canto’s Red Crossbill collection. As of this writing you can listen to and download recordings of types 2, 3, 4, 5, 9 and 10. I have posted a few mediocre recordings of Type 9, the South Hills Crossbill, which Benkman et al. 2009 have proposed as a separate species, Loxia sinesciuris.

In addition to the resources I’ve mentioned, there’s always the Macaulay Library, which is my favorite collection of online bird sounds. In an upcoming post I’ll try to put together an index to the types heard on the Macaulay recordings.

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